--[[
An implementation of Promises similar to Promise/A+.
]]
local ERROR_NON_PROMISE_IN_LIST = "Non-promise value passed into %s at index %s"
local ERROR_NON_LIST = "Please pass a list of promises to %s"
local ERROR_NON_FUNCTION = "Please pass a handler function to %s!"
local MODE_KEY_METATABLE = { __mode = "k" }
local function isCallable(value)
if type(value) == "function" then
return true
end
if type(value) == "table" then
local metatable = getmetatable(value)
if metatable and type(rawget(metatable, "__call")) == "function" then
return true
end
end
return false
end
--[[
Creates an enum dictionary with some metamethods to prevent common mistakes.
]]
local function makeEnum(enumName, members)
local enum = {}
for _, memberName in ipairs(members) do
enum[memberName] = memberName
end
return setmetatable(enum, {
__index = function(_, k)
error(string.format("%s is not in %s!", k, enumName), 2)
end,
__newindex = function()
error(string.format("Creating new members in %s is not allowed!", enumName), 2)
end,
})
end
--[=[
An object to represent runtime errors that occur during execution.
Promises that experience an error like this will be rejected with
an instance of this object.
@class Error
]=]
local Error
do
Error = {
Kind = makeEnum("Promise.Error.Kind", {
"ExecutionError",
"AlreadyCancelled",
"NotResolvedInTime",
"TimedOut",
}),
}
Error.__index = Error
function Error.new(options, parent)
options = options or {}
return setmetatable({
error = tostring(options.error) or "[This error has no error text.]",
trace = options.trace,
context = options.context,
kind = options.kind,
parent = parent,
createdTick = os.clock(),
createdTrace = debug.traceback(),
}, Error)
end
function Error.is(anything)
if type(anything) == "table" then
local metatable = getmetatable(anything)
if type(metatable) == "table" then
return rawget(anything, "error") ~= nil and type(rawget(metatable, "extend")) == "function"
end
end
return false
end
function Error.isKind(anything, kind)
assert(kind ~= nil, "Argument #2 to Promise.Error.isKind must not be nil")
return Error.is(anything) and anything.kind == kind
end
function Error:extend(options)
options = options or {}
options.kind = options.kind or self.kind
return Error.new(options, self)
end
function Error:getErrorChain()
local runtimeErrors = { self }
while runtimeErrors[#runtimeErrors].parent do
table.insert(runtimeErrors, runtimeErrors[#runtimeErrors].parent)
end
return runtimeErrors
end
function Error:__tostring()
local errorStrings = {
string.format("-- Promise.Error(%s) --", self.kind or "?"),
}
for _, runtimeError in ipairs(self:getErrorChain()) do
table.insert(
errorStrings,
table.concat({
runtimeError.trace or runtimeError.error,
runtimeError.context,
}, "\n")
)
end
return table.concat(errorStrings, "\n")
end
end
--[[
Packs a number of arguments into a table and returns its length.
Used to cajole varargs without dropping sparse values.
]]
local function pack(...)
return select("#", ...), { ... }
end
--[[
Returns first value (success), and packs all following values.
]]
local function packResult(success, ...)
return success, select("#", ...), { ... }
end
local function makeErrorHandler(traceback)
assert(traceback ~= nil, "traceback is nil")
return function(err)
-- If the error object is already a table, forward it directly.
-- Should we extend the error here and add our own trace?
if type(err) == "table" then
return err
end
return Error.new({
error = err,
kind = Error.Kind.ExecutionError,
trace = debug.traceback(tostring(err), 2),
context = "Promise created at:\n\n" .. traceback,
})
end
end
--[[
Calls a Promise executor with error handling.
]]
local function runExecutor(traceback, callback, ...)
return packResult(xpcall(callback, makeErrorHandler(traceback), ...))
end
--[[
Creates a function that invokes a callback with correct error handling and
resolution mechanisms.
]]
local function createAdvancer(traceback, callback, resolve, reject)
return function(...)
local ok, resultLength, result = runExecutor(traceback, callback, ...)
if ok then
resolve(unpack(result, 1, resultLength))
else
reject(result[1])
end
end
end
local function isEmpty(t)
return next(t) == nil
end
--[=[
An enum value used to represent the Promise's status.
@interface Status
@tag enum
@within Promise
.Started "Started" -- The Promise is executing, and not settled yet.
.Resolved "Resolved" -- The Promise finished successfully.
.Rejected "Rejected" -- The Promise was rejected.
.Cancelled "Cancelled" -- The Promise was cancelled before it finished.
]=]
--[=[
@prop Status Status
@within Promise
@readonly
@tag enums
A table containing all members of the `Status` enum, e.g., `Promise.Status.Resolved`.
]=]
--[=[
A Promise is an object that represents a value that will exist in the future, but doesn't right now.
Promises allow you to then attach callbacks that can run once the value becomes available (known as *resolving*),
or if an error has occurred (known as *rejecting*).
@class Promise
@__index prototype
]=]
local Promise = {
Error = Error,
Status = makeEnum("Promise.Status", { "Started", "Resolved", "Rejected", "Cancelled" }),
_getTime = os.clock,
_timeEvent = game:GetService("RunService").Heartbeat,
_unhandledRejectionCallbacks = {},
}
Promise.prototype = {}
Promise.__index = Promise.prototype
function Promise._new(traceback, callback, parent)
if parent ~= nil and not Promise.is(parent) then
error("Argument #2 to Promise.new must be a promise or nil", 2)
end
local self = {
-- The executor thread.
_thread = nil,
-- Used to locate where a promise was created
_source = traceback,
_status = Promise.Status.Started,
-- A table containing a list of all results, whether success or failure.
-- Only valid if _status is set to something besides Started
_values = nil,
-- Lua doesn't like sparse arrays very much, so we explicitly store the
-- length of _values to handle middle nils.
_valuesLength = -1,
-- Tracks if this Promise has no error observers..
_unhandledRejection = true,
-- Queues representing functions we should invoke when we update!
_queuedResolve = {},
_queuedReject = {},
_queuedFinally = {},
-- The function to run when/if this promise is cancelled.
_cancellationHook = nil,
-- The "parent" of this promise in a promise chain. Required for
-- cancellation propagation upstream.
_parent = parent,
-- Consumers are Promises that have chained onto this one.
-- We track them for cancellation propagation downstream.
_consumers = setmetatable({}, MODE_KEY_METATABLE),
}
if parent and parent._status == Promise.Status.Started then
parent._consumers[self] = true
end
setmetatable(self, Promise)
local function resolve(...)
self:_resolve(...)
end
local function reject(...)
self:_reject(...)
end
local function onCancel(cancellationHook)
if cancellationHook then
if self._status == Promise.Status.Cancelled then
cancellationHook()
else
self._cancellationHook = cancellationHook
end
end
return self._status == Promise.Status.Cancelled
end
self._thread = coroutine.create(function()
local ok, _, result = runExecutor(self._source, callback, resolve, reject, onCancel)
if not ok then
reject(result[1])
end
end)
task.spawn(self._thread)
return self
end
--[=[
Construct a new Promise that will be resolved or rejected with the given callbacks.
If you `resolve` with a Promise, it will be chained onto.
You can safely yield within the executor function and it will not block the creating thread.
```lua
local myFunction()
return Promise.new(function(resolve, reject, onCancel)
wait(1)
resolve("Hello world!")
end)
end
myFunction():andThen(print)
```
You do not need to use `pcall` within a Promise. Errors that occur during execution will be caught and turned into a rejection automatically. If `error()` is called with a table, that table will be the rejection value. Otherwise, string errors will be converted into `Promise.Error(Promise.Error.Kind.ExecutionError)` objects for tracking debug information.
You may register an optional cancellation hook by using the `onCancel` argument:
* This should be used to abort any ongoing operations leading up to the promise being settled.
* Call the `onCancel` function with a function callback as its only argument to set a hook which will in turn be called when/if the promise is cancelled.
* `onCancel` returns `true` if the Promise was already cancelled when you called `onCancel`.
* Calling `onCancel` with no argument will not override a previously set cancellation hook, but it will still return `true` if the Promise is currently cancelled.
* You can set the cancellation hook at any time before resolving.
* When a promise is cancelled, calls to `resolve` or `reject` will be ignored, regardless of if you set a cancellation hook or not.
:::caution
If the Promise is cancelled, the `executor` thread is closed with `coroutine.close` after the cancellation hook is called.
You must perform any cleanup code in the cancellation hook: any time your executor yields, it **may never resume**.
:::
@param executor (resolve: (...: any) -> (), reject: (...: any) -> (), onCancel: (abortHandler?: () -> ()) -> boolean) -> ()
@return Promise
]=]
function Promise.new(executor)
return Promise._new(debug.traceback(nil, 2), executor)
end
function Promise:__tostring()
return string.format("Promise(%s)", self._status)
end
--[=[
The same as [Promise.new](/api/Promise#new), except execution begins after the next `Heartbeat` event.
This is a spiritual replacement for `spawn`, but it does not suffer from the same [issues](https://eryn.io/gist/3db84579866c099cdd5bb2ff37947cec) as `spawn`.
```lua
local function waitForChild(instance, childName, timeout)
return Promise.defer(function(resolve, reject)
local child = instance:WaitForChild(childName, timeout)
;(child and resolve or reject)(child)
end)
end
```
@param executor (resolve: (...: any) -> (), reject: (...: any) -> (), onCancel: (abortHandler?: () -> ()) -> boolean) -> ()
@return Promise
]=]
function Promise.defer(executor)
local traceback = debug.traceback(nil, 2)
local promise
promise = Promise._new(traceback, function(resolve, reject, onCancel)
local connection
connection = Promise._timeEvent:Connect(function()
connection:Disconnect()
local ok, _, result = runExecutor(traceback, executor, resolve, reject, onCancel)
if not ok then
reject(result[1])
end
end)
end)
return promise
end
-- Backwards compatibility
Promise.async = Promise.defer
--[=[
Creates an immediately resolved Promise with the given value.
```lua
-- Example using Promise.resolve to deliver cached values:
function getSomething(name)
if cache[name] then
return Promise.resolve(cache[name])
else
return Promise.new(function(resolve, reject)
local thing = getTheThing()
cache[name] = thing
resolve(thing)
end)
end
end
```
@param ... any
@return Promise<...any>
]=]
function Promise.resolve(...)
local length, values = pack(...)
return Promise._new(debug.traceback(nil, 2), function(resolve)
resolve(unpack(values, 1, length))
end)
end
--[=[
Creates an immediately rejected Promise with the given value.
:::caution
Something needs to consume this rejection (i.e. `:catch()` it), otherwise it will emit an unhandled Promise rejection warning on the next frame. Thus, you should not create and store rejected Promises for later use. Only create them on-demand as needed.
:::
@param ... any
@return Promise<...any>
]=]
function Promise.reject(...)
local length, values = pack(...)
return Promise._new(debug.traceback(nil, 2), function(_, reject)
reject(unpack(values, 1, length))
end)
end
--[[
Runs a non-promise-returning function as a Promise with the
given arguments.
]]
function Promise._try(traceback, callback, ...)
local valuesLength, values = pack(...)
return Promise._new(traceback, function(resolve)
resolve(callback(unpack(values, 1, valuesLength)))
end)
end
--[=[
Begins a Promise chain, calling a function and returning a Promise resolving with its return value. If the function errors, the returned Promise will be rejected with the error. You can safely yield within the Promise.try callback.
:::info
`Promise.try` is similar to [Promise.promisify](#promisify), except the callback is invoked immediately instead of returning a new function.
:::
```lua
Promise.try(function()
return math.random(1, 2) == 1 and "ok" or error("Oh an error!")
end)
:andThen(function(text)
print(text)
end)
:catch(function(err)
warn("Something went wrong")
end)
```
@param callback (...: T...) -> ...any
@param ... T... -- Additional arguments passed to `callback`
@return Promise
]=]
function Promise.try(callback, ...)
return Promise._try(debug.traceback(nil, 2), callback, ...)
end
--[[
Returns a new promise that:
* is resolved when all input promises resolve
* is rejected if ANY input promises reject
]]
function Promise._all(traceback, promises, amount)
if type(promises) ~= "table" then
error(string.format(ERROR_NON_LIST, "Promise.all"), 3)
end
-- We need to check that each value is a promise here so that we can produce
-- a proper error rather than a rejected promise with our error.
for i, promise in pairs(promises) do
if not Promise.is(promise) then
error(string.format(ERROR_NON_PROMISE_IN_LIST, "Promise.all", tostring(i)), 3)
end
end
-- If there are no values then return an already resolved promise.
if #promises == 0 or amount == 0 then
return Promise.resolve({})
end
return Promise._new(traceback, function(resolve, reject, onCancel)
-- An array to contain our resolved values from the given promises.
local resolvedValues = {}
local newPromises = {}
-- Keep a count of resolved promises because just checking the resolved
-- values length wouldn't account for promises that resolve with nil.
local resolvedCount = 0
local rejectedCount = 0
local done = false
local function cancel()
for _, promise in ipairs(newPromises) do
promise:cancel()
end
end
-- Called when a single value is resolved and resolves if all are done.
local function resolveOne(i, ...)
if done then
return
end
resolvedCount = resolvedCount + 1
if amount == nil then
resolvedValues[i] = ...
else
resolvedValues[resolvedCount] = ...
end
if resolvedCount >= (amount or #promises) then
done = true
resolve(resolvedValues)
cancel()
end
end
onCancel(cancel)
-- We can assume the values inside `promises` are all promises since we
-- checked above.
for i, promise in ipairs(promises) do
newPromises[i] = promise:andThen(function(...)
resolveOne(i, ...)
end, function(...)
rejectedCount = rejectedCount + 1
if amount == nil or #promises - rejectedCount < amount then
cancel()
done = true
reject(...)
end
end)
end
if done then
cancel()
end
end)
end
--[=[
Accepts an array of Promises and returns a new promise that:
* is resolved after all input promises resolve.
* is rejected if *any* input promises reject.
:::info
Only the first return value from each promise will be present in the resulting array.
:::
After any input Promise rejects, all other input Promises that are still pending will be cancelled if they have no other consumers.
```lua
local promises = {
returnsAPromise("example 1"),
returnsAPromise("example 2"),
returnsAPromise("example 3"),
}
return Promise.all(promises)
```
@param promises {Promise<T>}
@return Promise<{T}>
]=]
function Promise.all(promises)
return Promise._all(debug.traceback(nil, 2), promises)
end
--[=[
Folds an array of values or promises into a single value. The array is traversed sequentially.
The reducer function can return a promise or value directly. Each iteration receives the resolved value from the previous, and the first receives your defined initial value.
The folding will stop at the first rejection encountered.
```lua
local basket = {"blueberry", "melon", "pear", "melon"}
Promise.fold(basket, function(cost, fruit)
if fruit == "blueberry" then
return cost -- blueberries are free!
else
-- call a function that returns a promise with the fruit price
return fetchPrice(fruit):andThen(function(fruitCost)
return cost + fruitCost
end)
end
end, 0)
```
@since v3.1.0
@param list {T | Promise<T>}
@param reducer (accumulator: U, value: T, index: number) -> U | Promise<U>
@param initialValue U
]=]
function Promise.fold(list, reducer, initialValue)
assert(type(list) == "table", "Bad argument #1 to Promise.fold: must be a table")
assert(isCallable(reducer), "Bad argument #2 to Promise.fold: must be a function")
local accumulator = Promise.resolve(initialValue)
return Promise.each(list, function(resolvedElement, i)
accumulator = accumulator:andThen(function(previousValueResolved)
return reducer(previousValueResolved, resolvedElement, i)
end)
end):andThen(function()
return accumulator
end)
end
--[=[
Accepts an array of Promises and returns a Promise that is resolved as soon as `count` Promises are resolved from the input array. The resolved array values are in the order that the Promises resolved in. When this Promise resolves, all other pending Promises are cancelled if they have no other consumers.
`count` 0 results in an empty array. The resultant array will never have more than `count` elements.
```lua
local promises = {
returnsAPromise("example 1"),
returnsAPromise("example 2"),
returnsAPromise("example 3"),
}
return Promise.some(promises, 2) -- Only resolves with first 2 promises to resolve
```
@param promises {Promise<T>}
@param count number
@return Promise<{T}>
]=]
function Promise.some(promises, count)
assert(type(count) == "number", "Bad argument #2 to Promise.some: must be a number")
return Promise._all(debug.traceback(nil, 2), promises, count)
end
--[=[
Accepts an array of Promises and returns a Promise that is resolved as soon as *any* of the input Promises resolves. It will reject only if *all* input Promises reject. As soon as one Promises resolves, all other pending Promises are cancelled if they have no other consumers.
Resolves directly with the value of the first resolved Promise. This is essentially [[Promise.some]] with `1` count, except the Promise resolves with the value directly instead of an array with one element.
```lua
local promises = {
returnsAPromise("example 1"),
returnsAPromise("example 2"),
returnsAPromise("example 3"),
}
return Promise.any(promises) -- Resolves with first value to resolve (only rejects if all 3 rejected)
```
@param promises {Promise<T>}
@return Promise<T>
]=]
function Promise.any(promises)
return Promise._all(debug.traceback(nil, 2), promises, 1):andThen(function(values)
return values[1]
end)
end
--[=[
Accepts an array of Promises and returns a new Promise that resolves with an array of in-place Statuses when all input Promises have settled. This is equivalent to mapping `promise:finally` over the array of Promises.
```lua
local promises = {
returnsAPromise("example 1"),
returnsAPromise("example 2"),
returnsAPromise("example 3"),
}
return Promise.allSettled(promises)
```
@param promises {Promise<T>}
@return Promise<{Status}>
]=]
function Promise.allSettled(promises)
if type(promises) ~= "table" then
error(string.format(ERROR_NON_LIST, "Promise.allSettled"), 2)
end
-- We need to check that each value is a promise here so that we can produce
-- a proper error rather than a rejected promise with our error.
for i, promise in pairs(promises) do
if not Promise.is(promise) then
error(string.format(ERROR_NON_PROMISE_IN_LIST, "Promise.allSettled", tostring(i)), 2)
end
end
-- If there are no values then return an already resolved promise.
if #promises == 0 then
return Promise.resolve({})
end
return Promise._new(debug.traceback(nil, 2), function(resolve, _, onCancel)
-- An array to contain our resolved values from the given promises.
local fates = {}
local newPromises = {}
-- Keep a count of resolved promises because just checking the resolved
-- values length wouldn't account for promises that resolve with nil.
local finishedCount = 0
-- Called when a single value is resolved and resolves if all are done.
local function resolveOne(i, ...)
finishedCount = finishedCount + 1
fates[i] = ...
if finishedCount >= #promises then
resolve(fates)
end
end
onCancel(function()
for _, promise in ipairs(newPromises) do
promise:cancel()
end
end)
-- We can assume the values inside `promises` are all promises since we
-- checked above.
for i, promise in ipairs(promises) do
newPromises[i] = promise:finally(function(...)
resolveOne(i, ...)
end)
end
end)
end
--[=[
Accepts an array of Promises and returns a new promise that is resolved or rejected as soon as any Promise in the array resolves or rejects.
:::warning
If the first Promise to settle from the array settles with a rejection, the resulting Promise from `race` will reject.
If you instead want to tolerate rejections, and only care about at least one Promise resolving, you should use [Promise.any](#any) or [Promise.some](#some) instead.
:::
All other Promises that don't win the race will be cancelled if they have no other consumers.
```lua
local promises = {
returnsAPromise("example 1"),
returnsAPromise("example 2"),
returnsAPromise("example 3"),
}
return Promise.race(promises) -- Only returns 1st value to resolve or reject
```
@param promises {Promise<T>}
@return Promise<T>
]=]
function Promise.race(promises)
assert(type(promises) == "table", string.format(ERROR_NON_LIST, "Promise.race"))
for i, promise in pairs(promises) do
assert(Promise.is(promise), string.format(ERROR_NON_PROMISE_IN_LIST, "Promise.race", tostring(i)))
end
return Promise._new(debug.traceback(nil, 2), function(resolve, reject, onCancel)
local newPromises = {}
local finished = false
local function cancel()
for _, promise in ipairs(newPromises) do
promise:cancel()
end
end
local function finalize(callback)
return function(...)
cancel()
finished = true
return callback(...)
end
end
if onCancel(finalize(reject)) then
return
end
for i, promise in ipairs(promises) do
newPromises[i] = promise:andThen(finalize(resolve), finalize(reject))
end
if finished then
cancel()
end
end)
end
--[=[
Iterates serially over the given an array of values, calling the predicate callback on each value before continuing.
If the predicate returns a Promise, we wait for that Promise to resolve before moving on to the next item
in the array.
:::info
`Promise.each` is similar to `Promise.all`, except the Promises are ran in order instead of all at once.
But because Promises are eager, by the time they are created, they're already running. Thus, we need a way to defer creation of each Promise until a later time.
The predicate function exists as a way for us to operate on our data instead of creating a new closure for each Promise. If you would prefer, you can pass in an array of functions, and in the predicate, call the function and return its return value.
:::
```lua
Promise.each({
"foo",
"bar",
"baz",
"qux"
}, function(value, index)
return Promise.delay(1):andThen(function()
print(("%d) Got %s!"):format(index, value))
end)
end)
--[[
(1 second passes)
> 1) Got foo!
(1 second passes)
> 2) Got bar!
(1 second passes)
> 3) Got baz!
(1 second passes)
> 4) Got qux!
]]
```
If the Promise a predicate returns rejects, the Promise from `Promise.each` is also rejected with the same value.
If the array of values contains a Promise, when we get to that point in the list, we wait for the Promise to resolve before calling the predicate with the value.
If a Promise in the array of values is already Rejected when `Promise.each` is called, `Promise.each` rejects with that value immediately (the predicate callback will never be called even once). If a Promise in the list is already Cancelled when `Promise.each` is called, `Promise.each` rejects with `Promise.Error(Promise.Error.Kind.AlreadyCancelled`). If a Promise in the array of values is Started at first, but later rejects, `Promise.each` will reject with that value and iteration will not continue once iteration encounters that value.
Returns a Promise containing an array of the returned/resolved values from the predicate for each item in the array of values.
If this Promise returned from `Promise.each` rejects or is cancelled for any reason, the following are true:
- Iteration will not continue.
- Any Promises within the array of values will now be cancelled if they have no other consumers.
- The Promise returned from the currently active predicate will be cancelled if it hasn't resolved yet.
@since 3.0.0
@param list {T | Promise<T>}
@param predicate (value: T, index: number) -> U | Promise<U>
@return Promise<{U}>
]=]
function Promise.each(list, predicate)
assert(type(list) == "table", string.format(ERROR_NON_LIST, "Promise.each"))
assert(isCallable(predicate), string.format(ERROR_NON_FUNCTION, "Promise.each"))
return Promise._new(debug.traceback(nil, 2), function(resolve, reject, onCancel)
local results = {}
local promisesToCancel = {}
local cancelled = false
local function cancel()
for _, promiseToCancel in ipairs(promisesToCancel) do
promiseToCancel:cancel()
end
end
onCancel(function()
cancelled = true
cancel()
end)
-- We need to preprocess the list of values and look for Promises.
-- If we find some, we must register our andThen calls now, so that those Promises have a consumer
-- from us registered. If we don't do this, those Promises might get cancelled by something else
-- before we get to them in the series because it's not possible to tell that we plan to use it
-- unless we indicate it here.
local preprocessedList = {}
for index, value in ipairs(list) do
if Promise.is(value) then
if value:getStatus() == Promise.Status.Cancelled then
cancel()
return reject(Error.new({
error = "Promise is cancelled",
kind = Error.Kind.AlreadyCancelled,
context = string.format(
"The Promise that was part of the array at index %d passed into Promise.each was already cancelled when Promise.each began.\n\nThat Promise was created at:\n\n%s",
index,
value._source
),
}))
elseif value:getStatus() == Promise.Status.Rejected then
cancel()
return reject(select(2, value:await()))
end
-- Chain a new Promise from this one so we only cancel ours
local ourPromise = value:andThen(function(...)
return ...
end)
table.insert(promisesToCancel, ourPromise)
preprocessedList[index] = ourPromise
else
preprocessedList[index] = value
end
end
for index, value in ipairs(preprocessedList) do
if Promise.is(value) then
local success
success, value = value:await()
if not success then
cancel()
return reject(value)
end
end
if cancelled then
return
end
local predicatePromise = Promise.resolve(predicate(value, index))
table.insert(promisesToCancel, predicatePromise)
local success, result = predicatePromise:await()
if not success then
cancel()
return reject(result)
end
results[index] = result
end
resolve(results)
end)
end
--[=[
Checks whether the given object is a Promise via duck typing. This only checks if the object is a table and has an `andThen` method.
@param object any
@return boolean -- `true` if the given `object` is a Promise.
]=]
function Promise.is(object)
if type(object) ~= "table" then
return false
end
local objectMetatable = getmetatable(object)
if objectMetatable == Promise then
-- The Promise came from this library.
return true
elseif objectMetatable == nil then
-- No metatable, but we should still chain onto tables with andThen methods
return isCallable(object.andThen)
elseif
type(objectMetatable) == "table"
and type(rawget(objectMetatable, "__index")) == "table"
and isCallable(rawget(rawget(objectMetatable, "__index"), "andThen"))
then
-- Maybe this came from a different or older Promise library.
return true
end
return false
end
--[=[
Wraps a function that yields into one that returns a Promise.
Any errors that occur while executing the function will be turned into rejections.
:::info
`Promise.promisify` is similar to [Promise.try](#try), except the callback is returned as a callable function instead of being invoked immediately.
:::
```lua
local sleep = Promise.promisify(wait)
sleep(1):andThen(print)
```
```lua
local isPlayerInGroup = Promise.promisify(function(player, groupId)
return player:IsInGroup(groupId)
end)
```
@param callback (...: any) -> ...any
@return (...: any) -> Promise
]=]
function Promise.promisify(callback)
return function(...)
return Promise._try(debug.traceback(nil, 2), callback, ...)
end
end
--[=[
Returns a Promise that resolves after `seconds` seconds have passed. The Promise resolves with the actual amount of time that was waited.
This function is **not** a wrapper around `wait`. `Promise.delay` uses a custom scheduler which provides more accurate timing. As an optimization, cancelling this Promise instantly removes the task from the scheduler.
:::warning
Passing `NaN`, infinity, or a number less than 1/60 is equivalent to passing 1/60.
:::
```lua
Promise.delay(5):andThenCall(print, "This prints after 5 seconds")
```
@function delay
@within Promise
@param seconds number
@return Promise<number>
]=]
do
-- uses a sorted doubly linked list (queue) to achieve O(1) remove operations and O(n) for insert
-- the initial node in the linked list
local first
local connection
function Promise.delay(seconds)
assert(type(seconds) == "number", "Bad argument #1 to Promise.delay, must be a number.")
-- If seconds is -INF, INF, NaN, or less than 1 / 60, assume seconds is 1 / 60.
-- This mirrors the behavior of wait()
if not (seconds >= 1 / 60) or seconds == math.huge then
seconds = 1 / 60
end
return Promise._new(debug.traceback(nil, 2), function(resolve, _, onCancel)
local startTime = Promise._getTime()
local endTime = startTime + seconds
local node = {
resolve = resolve,
startTime = startTime,
endTime = endTime,
}
if connection == nil then -- first is nil when connection is nil
first = node
connection = Promise._timeEvent:Connect(function()
local threadStart = Promise._getTime()
while first ~= nil and first.endTime < threadStart do
local current = first
first = current.next
if first == nil then
connection:Disconnect()
connection = nil
else
first.previous = nil
end
current.resolve(Promise._getTime() - current.startTime)
end
end)
else -- first is non-nil
if first.endTime < endTime then -- if `node` should be placed after `first`
-- we will insert `node` between `current` and `next`
-- (i.e. after `current` if `next` is nil)
local current = first
local next = current.next
while next ~= nil and next.endTime < endTime do
current = next
next = current.next
end
-- `current` must be non-nil, but `next` could be `nil` (i.e. last item in list)
current.next = node
node.previous = current
if next ~= nil then
node.next = next
next.previous = node
end
else
-- set `node` to `first`
node.next = first
first.previous = node
first = node
end
end
onCancel(function()
-- remove node from queue
local next = node.next
if first == node then
if next == nil then -- if `node` is the first and last
connection:Disconnect()
connection = nil
else -- if `node` is `first` and not the last
next.previous = nil
end
first = next
else
local previous = node.previous
-- since `node` is not `first`, then we know `previous` is non-nil
previous.next = next
if next ~= nil then
next.previous = previous
end
end
end)
end)
end
end
--[=[
Returns a new Promise that resolves if the chained Promise resolves within `seconds` seconds, or rejects if execution time exceeds `seconds`. The chained Promise will be cancelled if the timeout is reached.
Rejects with `rejectionValue` if it is non-nil. If a `rejectionValue` is not given, it will reject with a `Promise.Error(Promise.Error.Kind.TimedOut)`. This can be checked with [[Error.isKind]].
```lua
getSomething():timeout(5):andThen(function(something)
-- got something and it only took at max 5 seconds
end):catch(function(e)
-- Either getting something failed or the time was exceeded.
if Promise.Error.isKind(e, Promise.Error.Kind.TimedOut) then
warn("Operation timed out!")
else
warn("Operation encountered an error!")
end
end)
```
Sugar for:
```lua
Promise.race({
Promise.delay(seconds):andThen(function()
return Promise.reject(
rejectionValue == nil
and Promise.Error.new({ kind = Promise.Error.Kind.TimedOut })
or rejectionValue
)
end),
promise
})
```
@param seconds number
@param rejectionValue? any -- The value to reject with if the timeout is reached
@return Promise
]=]
function Promise.prototype:timeout(seconds, rejectionValue)
local traceback = debug.traceback(nil, 2)
return Promise.race({
Promise.delay(seconds):andThen(function()
return Promise.reject(rejectionValue == nil and Error.new({
kind = Error.Kind.TimedOut,
error = "Timed out",
context = string.format(
"Timeout of %d seconds exceeded.\n:timeout() called at:\n\n%s",
seconds,
traceback
),
}) or rejectionValue)
end),
self,
})
end
--[=[
Returns the current Promise status.
@return Status
]=]
function Promise.prototype:getStatus()
return self._status
end
--[[
Creates a new promise that receives the result of this promise.
The given callbacks are invoked depending on that result.
]]
function Promise.prototype:_andThen(traceback, successHandler, failureHandler)
self._unhandledRejection = false
-- If we are already cancelled, we return a cancelled Promise
if self._status == Promise.Status.Cancelled then
local promise = Promise.new(function() end)
promise:cancel()
return promise
end
-- Create a new promise to follow this part of the chain
return Promise._new(traceback, function(resolve, reject, onCancel)
-- Our default callbacks just pass values onto the next promise.
-- This lets success and failure cascade correctly!
local successCallback = resolve
if successHandler then
successCallback = createAdvancer(traceback, successHandler, resolve, reject)
end
local failureCallback = reject
if failureHandler then
failureCallback = createAdvancer(traceback, failureHandler, resolve, reject)
end
if self._status == Promise.Status.Started then
-- If we haven't resolved yet, put ourselves into the queue
table.insert(self._queuedResolve, successCallback)
table.insert(self._queuedReject, failureCallback)
onCancel(function()
-- These are guaranteed to exist because the cancellation handler is guaranteed to only
-- be called at most once
if self._status == Promise.Status.Started then
table.remove(self._queuedResolve, table.find(self._queuedResolve, successCallback))
table.remove(self._queuedReject, table.find(self._queuedReject, failureCallback))
end
end)
elseif self._status == Promise.Status.Resolved then
-- This promise has already resolved! Trigger success immediately.
successCallback(unpack(self._values, 1, self._valuesLength))
elseif self._status == Promise.Status.Rejected then
-- This promise died a terrible death! Trigger failure immediately.
failureCallback(unpack(self._values, 1, self._valuesLength))
end
end, self)
end
--[=[
Chains onto an existing Promise and returns a new Promise.
:::warning
Within the failure handler, you should never assume that the rejection value is a string. Some rejections within the Promise library are represented by [[Error]] objects. If you want to treat it as a string for debugging, you should call `tostring` on it first.
:::
You can return a Promise from the success or failure handler and it will be chained onto.
Calling `andThen` on a cancelled Promise returns a cancelled Promise.
:::tip
If the Promise returned by `andThen` is cancelled, `successHandler` and `failureHandler` will not run.
To run code no matter what, use [Promise:finally].
:::
@param successHandler (...: any) -> ...any
@param failureHandler? (...: any) -> ...any
@return Promise<...any>
]=]
function Promise.prototype:andThen(successHandler, failureHandler)
assert(successHandler == nil or isCallable(successHandler), string.format(ERROR_NON_FUNCTION, "Promise:andThen"))
assert(failureHandler == nil or isCallable(failureHandler), string.format(ERROR_NON_FUNCTION, "Promise:andThen"))
return self:_andThen(debug.traceback(nil, 2), successHandler, failureHandler)
end
--[=[
Shorthand for `Promise:andThen(nil, failureHandler)`.
Returns a Promise that resolves if the `failureHandler` worked without encountering an additional error.
:::warning
Within the failure handler, you should never assume that the rejection value is a string. Some rejections within the Promise library are represented by [[Error]] objects. If you want to treat it as a string for debugging, you should call `tostring` on it first.
:::
Calling `catch` on a cancelled Promise returns a cancelled Promise.
:::tip
If the Promise returned by `catch` is cancelled, `failureHandler` will not run.
To run code no matter what, use [Promise:finally].
:::
@param failureHandler (...: any) -> ...any
@return Promise<...any>
]=]
function Promise.prototype:catch(failureHandler)
assert(failureHandler == nil or isCallable(failureHandler), string.format(ERROR_NON_FUNCTION, "Promise:catch"))
return self:_andThen(debug.traceback(nil, 2), nil, failureHandler)
end
--[=[
Similar to [Promise.andThen](#andThen), except the return value is the same as the value passed to the handler. In other words, you can insert a `:tap` into a Promise chain without affecting the value that downstream Promises receive.
```lua
getTheValue()
:tap(print)
:andThen(function(theValue)
print("Got", theValue, "even though print returns nil!")
end)
```
If you return a Promise from the tap handler callback, its value will be discarded but `tap` will still wait until it resolves before passing the original value through.
@param tapHandler (...: any) -> ...any
@return Promise<...any>
]=]
function Promise.prototype:tap(tapHandler)
assert(isCallable(tapHandler), string.format(ERROR_NON_FUNCTION, "Promise:tap"))
return self:_andThen(debug.traceback(nil, 2), function(...)
local callbackReturn = tapHandler(...)
if Promise.is(callbackReturn) then
local length, values = pack(...)
return callbackReturn:andThen(function()
return unpack(values, 1, length)
end)
end
return ...
end)
end
--[=[
Attaches an `andThen` handler to this Promise that calls the given callback with the predefined arguments. The resolved value is discarded.
```lua
promise:andThenCall(someFunction, "some", "arguments")
```
This is sugar for
```lua
promise:andThen(function()
return someFunction("some", "arguments")
end)
```
@param callback (...: any) -> any
@param ...? any -- Additional arguments which will be passed to `callback`
@return Promise
]=]
function Promise.prototype:andThenCall(callback, ...)
assert(isCallable(callback), string.format(ERROR_NON_FUNCTION, "Promise:andThenCall"))
local length, values = pack(...)
return self:_andThen(debug.traceback(nil, 2), function()
return callback(unpack(values, 1, length))
end)
end
--[=[
Attaches an `andThen` handler to this Promise that discards the resolved value and returns the given value from it.
```lua
promise:andThenReturn("some", "values")
```
This is sugar for
```lua
promise:andThen(function()
return "some", "values"
end)
```
:::caution
Promises are eager, so if you pass a Promise to `andThenReturn`, it will begin executing before `andThenReturn` is reached in the chain. Likewise, if you pass a Promise created from [[Promise.reject]] into `andThenReturn`, it's possible that this will trigger the unhandled rejection warning. If you need to return a Promise, it's usually best practice to use [[Promise.andThen]].
:::
@param ... any -- Values to return from the function
@return Promise
]=]
function Promise.prototype:andThenReturn(...)
local length, values = pack(...)
return self:_andThen(debug.traceback(nil, 2), function()
return unpack(values, 1, length)
end)
end
--[=[
Cancels this promise, preventing the promise from resolving or rejecting. Does not do anything if the promise is already settled.
Cancellations will propagate upwards and downwards through chained promises.
Promises will only be cancelled if all of their consumers are also cancelled. This is to say that if you call `andThen` twice on the same promise, and you cancel only one of the child promises, it will not cancel the parent promise until the other child promise is also cancelled.
```lua
promise:cancel()
```
]=]
function Promise.prototype:cancel()
if self._status ~= Promise.Status.Started then
return
end
self._status = Promise.Status.Cancelled
if self._cancellationHook then
self._cancellationHook()
end
coroutine.close(self._thread)
if self._parent then
self._parent:_consumerCancelled(self)
end
for child in pairs(self._consumers) do
child:cancel()
end
self:_finalize()
end
--[[
Used to decrease the number of consumers by 1, and if there are no more,
cancel this promise.
]]
function Promise.prototype:_consumerCancelled(consumer)
if self._status ~= Promise.Status.Started then
return
end
self._consumers[consumer] = nil
if next(self._consumers) == nil then
self:cancel()
end
end
--[[
Used to set a handler for when the promise resolves, rejects, or is
cancelled.
]]
function Promise.prototype:_finally(traceback, finallyHandler)
self._unhandledRejection = false
local promise = Promise._new(traceback, function(resolve, reject, onCancel)
local handlerPromise
onCancel(function()
-- The finally Promise is not a proper consumer of self. We don't care about the resolved value.
-- All we care about is running at the end. Therefore, if self has no other consumers, it's safe to
-- cancel. We don't need to hold out cancelling just because there's a finally handler.
self:_consumerCancelled(self)
if handlerPromise then
handlerPromise:cancel()
end
end)
local finallyCallback = resolve
if finallyHandler then
finallyCallback = function(...)
local callbackReturn = finallyHandler(...)
if Promise.is(callbackReturn) then
handlerPromise = callbackReturn
callbackReturn
:finally(function(status)
if status ~= Promise.Status.Rejected then
resolve(self)
end
end)
:catch(function(...)
reject(...)
end)
else
resolve(self)
end
end
end
if self._status == Promise.Status.Started then
-- The promise is not settled, so queue this.
table.insert(self._queuedFinally, finallyCallback)
else
-- The promise already settled or was cancelled, run the callback now.
finallyCallback(self._status)
end
end)
return promise
end
--[=[
Set a handler that will be called regardless of the promise's fate. The handler is called when the promise is
resolved, rejected, *or* cancelled.
Returns a new Promise that:
- resolves with the same values that this Promise resolves with.
- rejects with the same values that this Promise rejects with.
- is cancelled if this Promise is cancelled.
If the value you return from the handler is a Promise:
- We wait for the Promise to resolve, but we ultimately discard the resolved value.
- If the returned Promise rejects, the Promise returned from `finally` will reject with the rejected value from the
*returned* promise.
- If the `finally` Promise is cancelled, and you returned a Promise from the handler, we cancel that Promise too.
Otherwise, the return value from the `finally` handler is entirely discarded.
:::note Cancellation
As of Promise v4, `Promise:finally` does not count as a consumer of the parent Promise for cancellation purposes.
This means that if all of a Promise's consumers are cancelled and the only remaining callbacks are finally handlers,
the Promise is cancelled and the finally callbacks run then and there.
Cancellation still propagates through the `finally` Promise though: if you cancel the `finally` Promise, it can cancel
its parent Promise if it had no other consumers. Likewise, if the parent Promise is cancelled, the `finally` Promise
will also be cancelled.
:::
```lua
local thing = createSomething()
doSomethingWith(thing)
:andThen(function()
print("It worked!")
-- do something..
end)
:catch(function()
warn("Oh no it failed!")
end)
:finally(function()
-- either way, destroy thing
thing:Destroy()
end)
```
@param finallyHandler (status: Status) -> ...any
@return Promise<...any>
]=]
function Promise.prototype:finally(finallyHandler)
assert(finallyHandler == nil or isCallable(finallyHandler), string.format(ERROR_NON_FUNCTION, "Promise:finally"))
return self:_finally(debug.traceback(nil, 2), finallyHandler)
end
--[=[
Same as `andThenCall`, except for `finally`.
Attaches a `finally` handler to this Promise that calls the given callback with the predefined arguments.
@param callback (...: any) -> any
@param ...? any -- Additional arguments which will be passed to `callback`
@return Promise
]=]
function Promise.prototype:finallyCall(callback, ...)
assert(isCallable(callback), string.format(ERROR_NON_FUNCTION, "Promise:finallyCall"))
local length, values = pack(...)
return self:_finally(debug.traceback(nil, 2), function()
return callback(unpack(values, 1, length))
end)
end
--[=[
Attaches a `finally` handler to this Promise that discards the resolved value and returns the given value from it.
```lua
promise:finallyReturn("some", "values")
```
This is sugar for
```lua
promise:finally(function()
return "some", "values"
end)
```
@param ... any -- Values to return from the function
@return Promise
]=]
function Promise.prototype:finallyReturn(...)
local length, values = pack(...)
return self:_finally(debug.traceback(nil, 2), function()
return unpack(values, 1, length)
end)
end
--[=[
Yields the current thread until the given Promise completes. Returns the Promise's status, followed by the values that the promise resolved or rejected with.
@yields
@return Status -- The Status representing the fate of the Promise
@return ...any -- The values the Promise resolved or rejected with.
]=]
function Promise.prototype:awaitStatus()
self._unhandledRejection = false
if self._status == Promise.Status.Started then
local thread = coroutine.running()
self
:finally(function()
task.spawn(thread)
end)
-- The finally promise can propagate rejections, so we attach a catch handler to prevent the unhandled
-- rejection warning from appearing
:catch(
function() end
)
coroutine.yield()
end
if self._status == Promise.Status.Resolved then
return self._status, unpack(self._values, 1, self._valuesLength)
elseif self._status == Promise.Status.Rejected then
return self._status, unpack(self._values, 1, self._valuesLength)
end
return self._status
end
local function awaitHelper(status, ...)
return status == Promise.Status.Resolved, ...
end
--[=[
Yields the current thread until the given Promise completes. Returns true if the Promise resolved, followed by the values that the promise resolved or rejected with.
:::caution
If the Promise gets cancelled, this function will return `false`, which is indistinguishable from a rejection. If you need to differentiate, you should use [[Promise.awaitStatus]] instead.
:::
```lua
local worked, value = getTheValue():await()
if worked then
print("got", value)
else
warn("it failed")
end
```
@yields
@return boolean -- `true` if the Promise successfully resolved
@return ...any -- The values the Promise resolved or rejected with.
]=]
function Promise.prototype:await()
return awaitHelper(self:awaitStatus())
end
local function expectHelper(status, ...)
if status ~= Promise.Status.Resolved then
error((...) == nil and "Expected Promise rejected with no value." or (...), 3)
end
return ...
end
--[=[
Yields the current thread until the given Promise completes. Returns the values that the promise resolved with.
```lua
local worked = pcall(function()
print("got", getTheValue():expect())
end)
if not worked then
warn("it failed")
end
```
This is essentially sugar for:
```lua
select(2, assert(promise:await()))
```
**Errors** if the Promise rejects or gets cancelled.
@error any -- Errors with the rejection value if this Promise rejects or gets cancelled.
@yields
@return ...any -- The values the Promise resolved with.
]=]
function Promise.prototype:expect()
return expectHelper(self:awaitStatus())
end
-- Backwards compatibility
Promise.prototype.awaitValue = Promise.prototype.expect
--[[
Intended for use in tests.
Similar to await(), but instead of yielding if the promise is unresolved,
_unwrap will throw. This indicates an assumption that a promise has
resolved.
]]
function Promise.prototype:_unwrap()
if self._status == Promise.Status.Started then
error("Promise has not resolved or rejected.", 2)
end
local success = self._status == Promise.Status.Resolved
return success, unpack(self._values, 1, self._valuesLength)
end
function Promise.prototype:_resolve(...)
if self._status ~= Promise.Status.Started then
if Promise.is((...)) then
(...):_consumerCancelled(self)
end
return
end
-- If the resolved value was a Promise, we chain onto it!
if Promise.is((...)) then
-- Without this warning, arguments sometimes mysteriously disappear
if select("#", ...) > 1 then
local message = string.format(
"When returning a Promise from andThen, extra arguments are " .. "discarded! See:\n\n%s",
self._source
)
warn(message)
end
local chainedPromise = ...
local promise = chainedPromise:andThen(function(...)
self:_resolve(...)
end, function(...)
local maybeRuntimeError = chainedPromise._values[1]
-- Backwards compatibility < v2
if chainedPromise._error then
maybeRuntimeError = Error.new({
error = chainedPromise._error,
kind = Error.Kind.ExecutionError,
context = "[No stack trace available as this Promise originated from an older version of the Promise library (< v2)]",
})
end
if Error.isKind(maybeRuntimeError, Error.Kind.ExecutionError) then
return self:_reject(maybeRuntimeError:extend({
error = "This Promise was chained to a Promise that errored.",
trace = "",
context = string.format(
"The Promise at:\n\n%s\n...Rejected because it was chained to the following Promise, which encountered an error:\n",
self._source
),
}))
end
self:_reject(...)
end)
if promise._status == Promise.Status.Cancelled then
self:cancel()
elseif promise._status == Promise.Status.Started then
-- Adopt ourselves into promise for cancellation propagation.
self._parent = promise
promise._consumers[self] = true
end
return
end
self._status = Promise.Status.Resolved
self._valuesLength, self._values = pack(...)
-- We assume that these callbacks will not throw errors.
for _, callback in ipairs(self._queuedResolve) do
coroutine.wrap(callback)(...)
end
self:_finalize()
end
function Promise.prototype:_reject(...)
if self._status ~= Promise.Status.Started then
return
end
self._status = Promise.Status.Rejected
self._valuesLength, self._values = pack(...)
-- If there are any rejection handlers, call those!
if not isEmpty(self._queuedReject) then
-- We assume that these callbacks will not throw errors.
for _, callback in ipairs(self._queuedReject) do
coroutine.wrap(callback)(...)
end
else
-- At this point, no one was able to observe the error.
-- An error handler might still be attached if the error occurred
-- synchronously. We'll wait one tick, and if there are still no
-- observers, then we should put a message in the console.
local err = tostring((...))
coroutine.wrap(function()
Promise._timeEvent:Wait()
-- Someone observed the error, hooray!
if not self._unhandledRejection then
return
end
-- Build a reasonable message
local message = string.format("Unhandled Promise rejection:\n\n%s\n\n%s", err, self._source)
for _, callback in ipairs(Promise._unhandledRejectionCallbacks) do
task.spawn(callback, self, unpack(self._values, 1, self._valuesLength))
end
if Promise.TEST then
-- Don't spam output when we're running tests.
return
end
warn(message)
end)()
end
self:_finalize()
end
--[[
Calls any :finally handlers. We need this to be a separate method and
queue because we must call all of the finally callbacks upon a success,
failure, *and* cancellation.
]]
function Promise.prototype:_finalize()
for _, callback in ipairs(self._queuedFinally) do
-- Purposefully not passing values to callbacks here, as it could be the
-- resolved values, or rejected errors. If the developer needs the values,
-- they should use :andThen or :catch explicitly.
coroutine.wrap(callback)(self._status)
end
self._queuedFinally = nil
self._queuedReject = nil
self._queuedResolve = nil
-- Clear references to other Promises to allow gc
if not Promise.TEST then
self._parent = nil
self._consumers = nil
end
task.defer(coroutine.close, self._thread)
end
--[=[
Chains a Promise from this one that is resolved if this Promise is already resolved, and rejected if it is not resolved at the time of calling `:now()`. This can be used to ensure your `andThen` handler occurs on the same frame as the root Promise execution.
```lua
doSomething()
:now()
:andThen(function(value)
print("Got", value, "synchronously.")
end)
```
If this Promise is still running, Rejected, or Cancelled, the Promise returned from `:now()` will reject with the `rejectionValue` if passed, otherwise with a `Promise.Error(Promise.Error.Kind.NotResolvedInTime)`. This can be checked with [[Error.isKind]].
@param rejectionValue? any -- The value to reject with if the Promise isn't resolved
@return Promise
]=]
function Promise.prototype:now(rejectionValue)
local traceback = debug.traceback(nil, 2)
if self._status == Promise.Status.Resolved then
return self:_andThen(traceback, function(...)
return ...
end)
else
return Promise.reject(rejectionValue == nil and Error.new({
kind = Error.Kind.NotResolvedInTime,
error = "This Promise was not resolved in time for :now()",
context = ":now() was called at:\n\n" .. traceback,
}) or rejectionValue)
end
end
--[=[
Repeatedly calls a Promise-returning function up to `times` number of times, until the returned Promise resolves.
If the amount of retries is exceeded, the function will return the latest rejected Promise.
```lua
local function canFail(a, b, c)
return Promise.new(function(resolve, reject)
-- do something that can fail
local failed, thing = doSomethingThatCanFail(a, b, c)
if failed then
reject("it failed")
else
resolve(thing)
end
end)
end
local MAX_RETRIES = 10
local value = Promise.retry(canFail, MAX_RETRIES, "foo", "bar", "baz") -- args to send to canFail
```
@since 3.0.0
@param callback (...: P) -> Promise<T>
@param times number
@param ...? P
@return Promise<T>
]=]
function Promise.retry(callback, times, ...)
assert(isCallable(callback), "Parameter #1 to Promise.retry must be a function")
assert(type(times) == "number", "Parameter #2 to Promise.retry must be a number")
local args, length = { ... }, select("#", ...)
return Promise.resolve(callback(...)):catch(function(...)
if times > 0 then
return Promise.retry(callback, times - 1, unpack(args, 1, length))
else
return Promise.reject(...)
end
end)
end
--[=[
Repeatedly calls a Promise-returning function up to `times` number of times, waiting `seconds` seconds between each
retry, until the returned Promise resolves.
If the amount of retries is exceeded, the function will return the latest rejected Promise.
@since v3.2.0
@param callback (...: P) -> Promise<T>
@param times number
@param seconds number
@param ...? P
@return Promise<T>
]=]
function Promise.retryWithDelay(callback, times, seconds, ...)
assert(isCallable(callback), "Parameter #1 to Promise.retry must be a function")
assert(type(times) == "number", "Parameter #2 (times) to Promise.retry must be a number")
assert(type(seconds) == "number", "Parameter #3 (seconds) to Promise.retry must be a number")
local args, length = { ... }, select("#", ...)
return Promise.resolve(callback(...)):catch(function(...)
if times > 0 then
Promise.delay(seconds):await()
return Promise.retryWithDelay(callback, times - 1, seconds, unpack(args, 1, length))
else
return Promise.reject(...)
end
end)
end
--[=[
Converts an event into a Promise which resolves the next time the event fires.
The optional `predicate` callback, if passed, will receive the event arguments and should return `true` or `false`, based on if this fired event should resolve the Promise or not. If `true`, the Promise resolves. If `false`, nothing happens and the predicate will be rerun the next time the event fires.
The Promise will resolve with the event arguments.
:::tip
This function will work given any object with a `Connect` method. This includes all Roblox events.
:::
```lua
-- Creates a Promise which only resolves when `somePart` is touched
-- by a part named `"Something specific"`.
return Promise.fromEvent(somePart.Touched, function(part)
return part.Name == "Something specific"
end)
```
@since 3.0.0
@param event Event -- Any object with a `Connect` method. This includes all Roblox events.
@param predicate? (...: P) -> boolean -- A function which determines if the Promise should resolve with the given value, or wait for the next event to check again.
@return Promise<P>
]=]
function Promise.fromEvent(event, predicate)
predicate = predicate or function()
return true
end
return Promise._new(debug.traceback(nil, 2), function(resolve, _, onCancel)
local connection
local shouldDisconnect = false
local function disconnect()
connection:Disconnect()
connection = nil
end
-- We use shouldDisconnect because if the callback given to Connect is called before
-- Connect returns, connection will still be nil. This happens with events that queue up
-- events when there's nothing connected, such as RemoteEvents
connection = event:Connect(function(...)
local callbackValue = predicate(...)
if callbackValue == true then
resolve(...)
if connection then
disconnect()
else
shouldDisconnect = true
end
elseif type(callbackValue) ~= "boolean" then
error("Promise.fromEvent predicate should always return a boolean")
end
end)
if shouldDisconnect and connection then
return disconnect()
end
onCancel(disconnect)
end)
end
--[=[
Registers a callback that runs when an unhandled rejection happens. An unhandled rejection happens when a Promise
is rejected, and the rejection is not observed with `:catch`.
The callback is called with the actual promise that rejected, followed by the rejection values.
@since v3.2.0
@param callback (promise: Promise, ...: any) -- A callback that runs when an unhandled rejection happens.
@return () -> () -- Function that unregisters the `callback` when called
]=]
function Promise.onUnhandledRejection(callback)
table.insert(Promise._unhandledRejectionCallbacks, callback)
return function()
local index = table.find(Promise._unhandledRejectionCallbacks, callback)
if index then
table.remove(Promise._unhandledRejectionCallbacks, index)
end
end
end
return Promise