[](https://travis-ci.org/jaemk/cached)
# cached
[](https://travis-ci.org/jaemk/cached)
[](https://crates.io/crates/cached)
[](https://docs.rs/cached)
> Caching structures and simplified function memoization
`cached` provides implementations of several caching structures as well as a handy macro
for defining memoized functions.
Memoized functions defined using `#[cached]`/`cached!` macros are thread-safe with the backing function-cache wrapped in a mutex.
The function-cache is **not** locked for the duration of the function's execution, so initial (on an empty cache)
concurrent calls of long-running functions with the same arguments will each execute fully and each overwrite
the memoized value as they complete. This mirrors the behavior of Python's `functools.lru_cache`.
See [`cached::stores` docs](https://docs.rs/cached/latest/cached/stores/index.html) for details about the
cache stores available.
**Features**
- `proc_macro`: (default) pull in proc macro support
- `async`: (default) Add `CachedAsync` trait
## Defining memoized functions using macros, `#[cached]` & `cached!`
**Notes on the proc-macro version #[cached]**
- enabled by default, but can be disabled by specifying `default-features = false`
(if you aren't using it and don't want to have to compile `syn`)
- supports more features at this point than the original collection of `cached!` macros do
- works with async functions
- see `cached_proc_macro/src/lib.rs` and examples below for more details on macro arguments
- see `examples/kitchen_sink_proc_macro.rs` for basic usage
The basic usage looks like:
```rust
use cached::proc_macro::cached;
/// Defines a function named `fib` that uses a cache implicitly named `FIB`.
/// By default, the cache will be the function's in all caps.
/// The following line is equivalent to #[cached(name = "FIB", unbound)]
#[cached]
fn fib(n: u64) -> u64 {
if n == 0 || n == 1 { return n }
fib(n-1) + fib(n-2)
}
```
```rust
use std::thread::sleep;
use std::time::Duration;
use cached::proc_macro::cached;
/// Use an lru cache with size 100 and a `(String, String)` cache key
#[cached(size=100)]
fn keyed(a: String, b: String) -> usize {
let size = a.len() + b.len();
sleep(Duration::new(size as u64, 0));
size
}
```
```rust
use std::thread::sleep;
use std::time::Duration;
use cached::proc_macro::cached;
/// Use a timed-lru cache with size 1, a TTL of 60s,
/// and a `(usize, usize)` cache key
#[cached(size=1, time=60)]
fn keyed(a: usize, b: usize) -> usize {
let total = a + b;
sleep(Duration::new(total as u64, 0));
total
}
pub fn main() {
keyed(1, 2); // Not cached, will sleep (1+2)s
keyed(1, 2); // Cached, no sleep
sleep(Duration::new(60, 0)); // Sleep for the TTL
keyed(1, 2); // 60s TTL has passed so the cached
// value has expired, will sleep (1+2)s
keyed(1, 2); // Cached, no sleep
keyed(2, 1); // New args, not cached, will sleep (2+1)s
keyed(1, 2); // Was evicted because of lru size of 1,
// will sleep (1+2)s
}
```
```rust
use std::thread::sleep;
use std::time::Duration;
use cached::proc_macro::cached;
/// Use a timed cache with a TTL of 60s
/// and a `(String, String)` cache key
#[cached(time=60)]
fn keyed(a: String, b: String) -> usize {
let size = a.len() + b.len();
sleep(Duration::new(size as u64, 0));
size
}
```
```rust
use cached::proc_macro::cached;
/// Cache a fallible function. Only `Ok` results are cached.
#[cached(size=1, result = true)]
fn keyed(a: String) -> Result<usize, ()> {
do_something_fallible()?;
Ok(a.len())
}
```
```rust
use cached::proc_macro::cached;
/// Cache an optional function. Only `Some` results are cached.
#[cached(size=1, option = true)]
fn keyed(a: String) -> Option<usize> {
if a == "a" {
Some(a.len())
} else {
None
}
}
```
```rust
use cached::proc_macro::cached;
use cached::Return;
/// Get a `cached::Return` value that indicates
/// whether the value returned came from the cache:
/// `cached::Return.was_cached`.
/// Use an LRU cache with a TTL of 60s
/// and a `String` cache key.
#[cached(size=1, with_cached_flag = true)]
fn calculate(a: String) -> Return<String> {
Return::new(a)
}
pub fn main() {
let r = calculate("a".to_string());
assert!(!r.was_cached);
let r = calculate("a".to_string());
assert!(r.was_cached);
// Return<String> derefs to String
assert_eq!(r.to_uppercase(), "A");
}
```
```rust
use cached::proc_macro::cached;
use cached::Return;
/// Same as the previous, but returning a Result
#[cached(size=1, result = true, with_cached_flag = true)]
fn calculate(a: String) -> Result<Return<usize>, ()> {
do_something_fallible()?;
Ok(Return::new(a.len()))
}
pub fn main() {
match calculate("a".to_string()) {
Err(e) => eprintln!("error: {:?}", e),
Ok(r) => {
println!("value: {:?}, was cached: {}", *r, r.was_cached);
// value: "a", was cached: true
}
}
}
```
```rust
use cached::proc_macro::cached;
use cached::Return;
/// Same as the previous, but returning an Option
#[cached(size=1, option = true, with_cached_flag = true)]
fn calculate(a: String) -> Option<Return<usize>> {
if a == "a" {
Some(Return::new(a.len()))
} else {
None
}
}
pub fn main() {
if let Some(a) = calculate("a".to_string()) {
println!("value: {:?}, was cached: {}", *a, a.was_cached);
// value: "a", was cached: true
}
}
```
```rust
use std::thread::sleep;
use std::time::Duration;
use cached::proc_macro::cached;
use cached::SizedCache;
/// Use an explicit cache-type with a custom creation block and custom cache-key generating block
#[cached(
type = "SizedCache<String, usize>",
create = "{ SizedCache::with_size(100) }",
convert = r#"{ format!("{}{}", a, b) }"#
)]
fn keyed(a: &str, b: &str) -> usize {
let size = a.len() + b.len();
sleep(Duration::new(size as u64, 0));
size
}
```
----
`#[cached]`/`cached!` defined functions will have their results cached using the function's arguments as a key
(or a specific expression when using `cached_key!`).
When a `cached!` defined function is called, the function's cache is first checked for an already
computed (and still valid) value before evaluating the function body.
Due to the requirements of storing arguments and return values in a global cache:
- Function return types must be owned and implement `Clone`
- Function arguments must either be owned and implement `Hash + Eq + Clone` OR the `cached_key!`
macro must be used to convert arguments into an owned + `Hash + Eq + Clone` type.
- Arguments and return values will be `cloned` in the process of insertion and retrieval.
- `#[cached]`/`cached!` functions should not be used to produce side-effectual results!
- `#[cached]`/`cached!` functions cannot live directly under `impl` blocks since `cached!` expands to a
`once_cell` initialization and a function definition.
- `#[cached]`/`cached!` functions cannot accept `Self` types as a parameter.
**NOTE**: Any custom cache that implements `cached::Cached` can be used with the `cached` macros in place of the built-ins.
See [`examples`](https://github.com/jaemk/cached/tree/master/examples) for basic usage of proc-macro &
macro-rules macros and an example of implementing a custom cache-store.
### `cached!` and `cached_key!` Usage & Options:
There are several options depending on how explicit you want to be. See below for a full syntax breakdown.
1.) Using the shorthand will use an unbounded cache.
```rust
#[macro_use] extern crate cached;
/// Defines a function named `fib` that uses a cache named `FIB`
cached!{
FIB;
fn fib(n: u64) -> u64 = {
if n == 0 || n == 1 { return n }
fib(n-1) + fib(n-2)
}
}
```
2.) Using the full syntax requires specifying the full cache type and providing
an instance of the cache to use. Note that the cache's key-type is a tuple
of the function argument types. If you would like fine grained control over
the key, you can use the `cached_key!` macro.
The following example uses a `SizedCache` (LRU):
```rust
#[macro_use] extern crate cached;
use std::thread::sleep;
use std::time::Duration;
use cached::SizedCache;
/// Defines a function `compute` that uses an LRU cache named `COMPUTE` which has a
/// size limit of 50 items. The `cached!` macro will implicitly combine
/// the function arguments into a tuple to be used as the cache key.
cached!{
COMPUTE: SizedCache<(u64, u64), u64> = SizedCache::with_size(50);
fn compute(a: u64, b: u64) -> u64 = {
sleep(Duration::new(2, 0));
return a * b;
}
}
```
3.) The `cached_key` macro functions identically, but allows you to define the
cache key as an expression.
```rust
#[macro_use] extern crate cached;
use std::thread::sleep;
use std::time::Duration;
use cached::SizedCache;
/// Defines a function named `length` that uses an LRU cache named `LENGTH`.
/// The `Key = ` expression is used to explicitly define the value that
/// should be used as the cache key. Here the borrowed arguments are converted
/// to an owned string that can be stored in the global function cache.
cached_key!{
LENGTH: SizedCache<String, usize> = SizedCache::with_size(50);
Key = { format!("{}{}", a, b) };
fn length(a: &str, b: &str) -> usize = {
let size = a.len() + b.len();
sleep(Duration::new(size as u64, 0));
size
}
}
```
4.) The `cached_result` and `cached_key_result` macros function similarly to `cached`
and `cached_key` respectively but the cached function needs to return `Result`
(or some type alias like `io::Result`). If the function returns `Ok(val)` then `val`
is cached, but errors are not. Note that only the success type needs to implement
`Clone`, _not_ the error type. When using `cached_result` and `cached_key_result`,
the cache type cannot be derived and must always be explicitly specified.
```rust
#[macro_use] extern crate cached;
use cached::UnboundCache;
/// Cache the successes of a function.
/// To use `cached_key_result` add a key function as in `cached_key`.
cached_result!{
MULT: UnboundCache<(u64, u64), u64> = UnboundCache::new(); // Type must always be specified
fn mult(a: u64, b: u64) -> Result<u64, ()> = {
if a == 0 || b == 0 {
return Err(());
} else {
return Ok(a * b);
}
}
}
```
## Syntax
The common macro syntax is:
```rust
cached_key!{
CACHE_NAME: CacheType = CacheInstance;
Key = KeyExpression;
fn func_name(arg1: arg_type, arg2: arg_type) -> return_type = {
// do stuff like normal
return_type
}
}
```
Where:
- `CACHE_NAME` is the unique name used to hold a `static ref` to the cache
- `CacheType` is the full type of the cache
- `CacheInstance` is any expression that yields an instance of `CacheType` to be used
as the cache-store, followed by `;`
- When using the `cached_key!` macro, the "Key" line must be specified. This line must start with
the literal tokens `Key = `, followed by an expression that evaluates to the key, followed by `;`
- `fn func_name(arg1: arg_type) -> return_type` is the same form as a regular function signature, with the exception
that functions with no return value must be explicitly stated (e.g. `fn func_name(arg: arg_type) -> ()`)
- The expression following `=` is the function body assigned to `func_name`. Note, the function
body can make recursive calls to its cached-self (`func_name`).
# Fine grained control using `cached_control!`
The `cached_control!` macro allows you to provide expressions that get plugged into key areas
of the memoized function. While the `cached` and `cached_result` variants are adequate for most
scenarios, it can be useful to have the ability to customize the macro's functionality.
```rust
#[macro_use] extern crate cached;
use cached::UnboundCache;
/// The following usage plugs in expressions to make the macro behave like
/// the `cached_result!` macro.
cached_control!{
CACHE: UnboundCache<String, String> = UnboundCache::new();
// Use an owned copy of the argument `input` as the cache key
Key = { input.to_owned() };
// If a cached value exists, it will bind to `cached_val` and
// a `Result` will be returned containing a copy of the cached
// evaluated body. This will return before the function body
// is executed.
PostGet(cached_val) = { return Ok(cached_val.clone()) };
// The result of executing the function body will be bound to
// `body_result`. In this case, the function body returns a `Result`.
// We match on the `Result`, returning an early `Err` if the function errored.
// Otherwise, we pass on the function's result to be cached.
PostExec(body_result) = {
match body_result {
Ok(v) => v,
Err(e) => return Err(e),
}
};
// When inserting the value into the cache we bind
// the to-be-set-value to `set_value` and give back a copy
// of it to be inserted into the cache
Set(set_value) = { set_value.clone() };
// Before returning, print the value that will be returned
Return(return_value) = {
println!("{}", return_value);
Ok(return_value)
};
fn can_fail(input: &str) -> Result<String, String> = {
let len = input.len();
if len < 3 { Ok(format!("{}-{}", input, len)) }
else { Err("too big".to_string()) }
}
}
```
License: MIT