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use core::marker::PhantomData;
/**
A marker trait that is used to represent unique type in Rust.
`mononym` guarantees that any two `impl Name` generated by
the library are always considered distinct types by Rust.
This is mainly used as a type parameter inside types such as
[`Seed`]. For example, the type `Seed<impl Name>`
is used to represent a unique seed type with a fresh type
`impl Name` being its name.
*/
pub trait Name: Send + Sync + Sealed
{
}
/**
A marker trait that is used to mark a type-level name being bound to
a Rust value of the given type `T`. This helps ensure that functions
that are generic over type-level names are "well-typed", with
each name "having" their own type through `HasType`.
With `Name` being a supertrait of `HasType`, this means that any
name type can have their "type" erased by downcasting the type from
`impl HasType<T>` to `impl Name`.
This trait is used as a type parameter inside [`Named`], so that the
type `Named<impl HasType<T>, T>` also attaches the type information
to the type-level name associated with the named value.
*/
pub trait HasType<T>: Name
{
}
/**
Represents a named value with a unique type-level name. `monoym`
guarantees that there can never be two Rust values of the same
type `Named<N, T>`. With that, the name type `N` can be used to
uniquely identify the underlying value at the type level.
To ensure that functions that are generic over names are well-typed
`Named` also requires the name type `N` to satisfy the trait bound
[`HasType<T>`]. Although this may introduce more boilerplate,
it also helps programmers to always annotate the type of names
when defining new generic functions.
*/
pub struct Named<N: HasType<T>, T>(T, PhantomData<N>);
/**
A unique seed type for generating new unique names. `mononym`
guarantees that there can never be two seed value of the same type
`Seed<N>` with the same name type `N`.
A `Seed` value is required to generate new names for values to be
used in types such as [`Named`]. A seed value can be obtained by
either making functions accept a `Seed<impl Name>` as its argument,
or creating fresh `Seed` value using [`with_seed`].
*/
pub struct Seed<N>(PhantomData<N>);
/**
Turns a lifetime `'name` into a unique type `Life<'name>`
with an invariant phantom lifetime. `Life` implements [`Name`]
so that it can be turned into a unique `impl Name`.
The body [`PhantomData`] has a phantom type `*mut &'name ()`
to ensure that overlapping lifetimes such as
`'name1: 'name2` are treated as distinct types and cannot be
coerced into one another, unless they are exactly the same.
For example, the following test should fail:
```rust,compile_fail
# use mononym::*;
fn same<T>(_: T, _: T) {}
fn same_life<'name1, 'name2: 'name1>(
life1: Life<'name1>,
life2: Life<'name2>
) {
same(life1, life2); // error
}
```
*/
pub struct Life<'name>(PhantomData<*mut &'name ()>);
struct SomeName<N>(PhantomData<N>);
impl<N: HasType<T>, T> Named<N, T>
{
/**
Get a reference to the underlying value of the named value.
`mononym` does not provide access to mutable reference to
the underlying value, as mutation may invalidate the proofs
of pre-conditions constructed from the original value.
When using `Named`, it is up to the user to ensure that there
is no accidental
[interior mutability](https://doc.rust-lang.org/reference/interior-mutability.html)
provided by the value type `T`. Otherwise, user must take
into consideration of the possibility of interior mutability
and ensure that the invariants assumed by the proofs defined
cannot be violated.
*/
pub fn value<'a>(&'a self) -> &'a T
{
&self.0
}
/**
Consume the named value and turn it back into the underlying value.
After this, the underlying value is no longer associated with the
type-level name, and can be safely mutated.
Even though the named value is destroyed, the type-level name
can still continue to present in other places such as proof objects.
This can be useful for functions that only require proofs about
a value, without requiring access to the value itself.
*/
pub fn into_value(self) -> T
{
self.0
}
}
impl<N> Seed<N>
{
/**
Consumes the seed and returns a value with a unique type
`impl Name`. The value on its own do not have much use,
however it can be used as a proxy type for users to
define their own name-based abstractions.
*/
pub fn new_name(self) -> impl Name
{
unsafe_new_name(|| {})
}
/**
Consumes the seed and a value of type `T` and turn it into
a named value [`Named<impl HasType<T>, T>`]. The returned
named value have a unique type-level name that implements
both [`Name`] and [`HasType<T>`].
*/
pub fn new_named<T>(
self,
value: T,
) -> Named<impl HasType<T>, T>
{
unsafe_new_named(unsafe_new_name_with_type(|| {}), value)
}
/**
Consumes the seed and returns two new seeds `Seed<impl Name>`
with unique names and thus of different types.
`mononym` guarantees that each replicated seed will generate
different names, thereby guarantee that the names are always
unique.
For example, the following code should fail with compile error:
```rust,compile_fail
# use mononym::*;
fn same<T>(_: T, _: T) {}
fn test(seed: Seed<impl Name>) {
let (seed1, seed2) = seed.replicate();
same(seed1, seed2); // error
same(seed1.new_named(()), seed2.new_named(())); // error
}
```
For convenience, `mononym` also provides the replicate functions
from [`Seed::replicate_3`] up to [`Seed::replicate_8`] to allow
easy replication of the seed for 2-8 times. User can call the
replicate functions multiple times if they need more than
8 seed replications, which should be rarely happen.
*/
pub fn replicate(self) -> (Seed<impl Name>, Seed<impl Name>)
{
(unsafe_new_seed(|| {}), unsafe_new_seed(|| {}))
}
}
/**
This trait is not exported so that the Name trait
becomes a [_sealed trait_](https://rust-lang.github.io/api-guidelines/future-proofing.html)
which user cannot provide custom implementation to.
*/
pub trait Sealed
{
}
impl<N> Sealed for SomeName<N> where N: Send + Sync {}
impl<N> Name for SomeName<N> where N: Send + Sync {}
impl<N, T> HasType<T> for SomeName<N> where N: Send + Sync {}
unsafe impl<'name> Send for Life<'name> {}
unsafe impl<'name> Sync for Life<'name> {}
impl<'name> Sealed for Life<'name> {}
impl<'name> Name for Life<'name> {}
/**
Provides the continuation closure with a unique [`Seed`] with a unique lifetime
`'name` and a unique name [`Life<'name>`](Life).
This is achieved using
[higher-ranked trait bounds](https://doc.rust-lang.org/nomicon/hrtb.html)
by requiring the continuation closure to work for all lifetime `'name`.
It is safe to have multiple nested calls to `with_seed`, as each call
will generate new seed type with a unique `'name` lifetime. For example,
the following code should fail to compile:
```rust,compile_fail
# use mononym::*;
fn same<T>(_: T, _: T) {}
with_seed(|seed1| {
with_seed(|seed2| {
same(seed1, seed2); // error
same(seed1.new_named(1), seed2.new_named(1)); // error
});
});
```
The function allows the continuation closure to return any concrete type
`R`, provided that the return type `R` does not depend on the provided
`Seed` type in some way. This means that types such as [`Name`],
[`Named`], and [`Seed`] cannot be used as a return value, as Rust
consider that as allowing the lifetime `'name` to escape. For example,
the following code should fail to compile:
```rust,compile_fail
# use mononym::*;
let res = with_seed(|seed| { seed.new_named(42).into_value() }); // ok
let res = with_seed(|seed| { seed }); // error
let res = with_seed(|seed| { seed.new_name() }); // error
let res = with_seed(|seed| { seed.new_named(42) }); // error
```
*/
pub fn with_seed<R>(cont: impl for<'name> FnOnce(Seed<Life<'name>>) -> R) -> R
{
cont(Seed(PhantomData))
}
fn unsafe_new_name<F>(_: F) -> impl Name
where
F: Send + Sync,
{
SomeName(PhantomData::<F>)
}
fn unsafe_new_name_with_type<F, T>(_: F) -> impl HasType<T>
where
F: Send + Sync,
{
SomeName(PhantomData::<F>)
}
fn unsafe_new_seed<F>(_: F) -> Seed<impl Name>
where
F: Send + Sync,
{
Seed(PhantomData::<SomeName<F>>)
}
fn unsafe_new_named<Name: HasType<T>, T>(
_: Name,
value: T,
) -> Named<Name, T>
{
Named(value, PhantomData)
}
impl<N: Name> Seed<N>
{
pub fn replicate_3(
self
) -> (Seed<impl Name>, Seed<impl Name>, Seed<impl Name>)
{
(
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
)
}
pub fn replicate_4(
self
) -> (
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
)
{
(
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
)
}
pub fn replicate_5(
self
) -> (
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
)
{
(
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
)
}
pub fn replicate_6(
self
) -> (
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
)
{
(
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
)
}
pub fn replicate_7(
self
) -> (
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
)
{
(
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
)
}
pub fn replicate_8(
self
) -> (
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
Seed<impl Name>,
)
{
(
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
unsafe_new_seed(|| {}),
)
}
}