impls-1.0.3/Cargo.toml.orig 0100644 0000765 0000024 00000001031 13602702455 0013744 0 ustar 00 0000000 0000000 [package]
name = "impls"
version = "1.0.3"
authors = ["Nikolai Vazquez", "Nadrieril Feneanar"]
license = "MIT OR Apache-2.0"
description = "Determine if a type implements a logical trait expression."
repository = "https://github.com/nvzqz/impls"
homepage = "https://github.com/nvzqz/impls"
documentation = "https://docs.rs/impls"
categories = ["no-std", "rust-patterns", "development-tools::testing"]
keywords = ["impl", "trait", "test", "macro"]
readme = "README.md"
include = ["Cargo.toml", "src", "README*", "CHANGELOG*", "LICENSE*"]
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[package]
name = "impls"
version = "1.0.3"
authors = ["Nikolai Vazquez", "Nadrieril Feneanar"]
include = ["Cargo.toml", "src", "README*", "CHANGELOG*", "LICENSE*"]
description = "Determine if a type implements a logical trait expression."
homepage = "https://github.com/nvzqz/impls"
documentation = "https://docs.rs/impls"
readme = "README.md"
keywords = ["impl", "trait", "test", "macro"]
categories = ["no-std", "rust-patterns", "development-tools::testing"]
license = "MIT OR Apache-2.0"
repository = "https://github.com/nvzqz/impls"
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impls-1.0.3/README.md 0100644 0000765 0000024 00000027470 13602702455 0012353 0 ustar 00 0000000 0000000
Determine if a type implements a logical trait
expression[**?**](#logical-trait-expression), brought to you by
[@NikolaiVazquez]!
This library defines [`impls!`], a macro[**?**](#macro) that returns
a [`bool`] indicating whether a type implements a boolean-like expression over a
set of traits[**?**](#trait).
```rust
assert!(impls!(String: Clone & !Copy & Send & Sync));
```
See ["Examples"](#examples) for detailed use cases and, if you're brave, see
["Trait-Dependent Type Sizes"](#trait-dependent-type-sizes) for some cursed
code.
## Index
- [Reasoning](#reasoning)
- [Usage](#usage)
- [Vocabulary](#vocabulary)
- [Macro](#macro)
- [Trait](#trait)
- [Logical Trait Expression](#logical-trait-expression)
- [Examples](#examples)
- [Constant Evaluation](#constant-evaluation)
- [Precedence and Nesting](#precedence-and-nesting)
- [Mutual Exclusion](#mutual-exclusion)
- [Reference Types](#reference-types)
- [Unsized Types](#unsized-types)
- [Generic Types](#generic-types)
- [Lifetimes](#lifetimes)
- [Trait-Dependent Type Sizes](#trait-dependent-type-sizes)
- [Authors](#authors)
- [License](#license)
## Reasoning
As a library author, it's important to ensure that your API remains stable.
Trait implementations are part of API stability. For example: if you
accidentally introduce an inner type that makes your publicly-exposed type no
longer be [`Send`] or [`Sync`], you've now broken your API without noticing it!
The most common case of this happening is adding a [raw pointer][ptr]
(i.e. `*const T`, `*mut T`) as a type field.
By checking situations like this with [`impls!`], either at [compile-time] or in
a unit test, you can ensure that no API-breaking changes are made without
noticing until it's too late.
## Usage
This crate is available [on crates.io][crate] and can be used by adding the
following to your project's [`Cargo.toml`]:
```toml
[dependencies]
impls = "1"
```
and this to your crate root (`main.rs` or `lib.rs`):
```rust
#[macro_use]
extern crate impls;
```
When using [Rust 2018 edition][2018], the following import can help if
having `#[macro_use]` is undesirable.
```rust
use impls::impls;
```
## Vocabulary
This documentation uses jargon that may be new to inexperienced Rust users.
This section exists to make these terms easier to understand. Feel free to
skip this section if these are already familiar to you.
### Macro
In Rust, macros are functions over the [abstract syntax tree (AST)][AST].
They map input tokens to output tokens by performing some operation over
them through a set of rules. Because of this, only their outputs are ever
type-checked.
If you wish to learn about implementing macros, I recommend:
- [The Little Book of Rust Macros](https://danielkeep.github.io/tlborm/book/index.html)
- ["Macros" - The Rust Programming Language](https://doc.rust-lang.org/book/ch19-06-macros.html)
- ["Macros" - The Rust Reference](https://doc.rust-lang.org/stable/reference/macros.html)
- ["Macros By Example" - The Rust Reference](https://doc.rust-lang.org/stable/reference/macros-by-example.html)
To use this crate, you do not need to know how macros are defined.
### Trait
In Rust, traits are a way of defining a generalized property. They should be
thought of expressing what a type is capable of doing. For example: if a
type implements [`Into`] for some type `T`, then we know it can be converted
into `T` by just calling the `.into()` method on it.
If you wish to learn about traits in detail, I recommend:
- ["Traits: Defining Shared Behavior" - The Rust Programming Language](https://doc.rust-lang.org/book/ch10-02-traits.html)
- ["Traits" - The Rust Reference](https://doc.rust-lang.org/stable/reference/items/traits.html)
### Logical Trait Expression
In this crate, traits should be thought of as [`bool`]s where the condition
is whether the given type implements the trait or not.
An expression can be formed from these trait operations:
- And (`&`): also known as [logical conjunction], this returns `true` if
**both** operands are `true`. This is usually defined in Rust via the
[`BitAnd`] trait.
- Or (`|`): also known as [logical disjunction], this returns `true` if
**either** of two operands is `true`. This is usually defined in Rust via
the [`BitOr`] trait.
- Exclusive-or (`^`): also known as [exclusive disjunction], this returns
`true` if **only one** of two operands is `true`. This is usually defined
in Rust via the [`BitXor`] trait.
- Not (`!`): a negation that returns `false` if the operand is `true`, or
`true` if the operand is `false`. This is usually defined in Rust via the
[`Not`] trait.
See ["Precedence and Nesting"](#precedence-and-nesting) for information
about the order in which these operations are performed.
## Examples
This macro works in every type context. See below for use cases.
### Constant Evaluation
Because types are [compile-time] constructs, the result of this macro can be
used as a `const` value:
```rust
const IMPLS: bool = impls!(u8: From);
```
Using [`static_assertions`], we can fail to compile if the trait expression
evaluates to `false`:
```rust
const_assert!(impls!(*const u8: Send | Sync));
```
### Precedence and Nesting
Trait operations abide by [Rust's expression precedence][precedence]. To
define a custom order of operations (e.g. left-to-right), simply nest the
expressions with parentheses.
```rust
let pre = impls!(u64: From | From ^ From & From);
let ltr = impls!(u64: ((From | From) ^ From) & From);
assert_eq!(pre, true | true ^ true & true);
assert_ne!(pre, ltr);
```
### Mutual Exclusion
Because exclusive-or (`^`) is a trait operation, we can check that a type
implements one of two traits, but not both:
```rust
struct T;
trait Foo {}
trait Bar {}
impl Foo for T {}
assert!(impls!(T: Foo ^ Bar));
```
### Reference Types
Something that's surprising to many Rust users is that [`&mut T`] _does not_
implement [`Copy`] _nor_ [`Clone`]:
```rust
assert!(impls!(&mut u32: !Copy & !Clone));
```
Surely you're thinking now that this macro must be broken, because you've
been able to reuse `&mut T` throughout your lifetime with Rust. This works
because, in certain contexts, the compiler silently adds "re-borrows"
(`&mut *ref`) with a shorter lifetime and shadows the original. In reality,
`&mut T` is a move-only type.
### Unsized Types
There's a variety of types in Rust that don't implement [`Sized`]:
```rust
// Slices store their size with their pointer.
assert!(impls!(str: !Sized));
assert!(impls!([u8]: !Sized));
// Trait objects store their size in a vtable.
trait Foo {}
assert!(impls!(dyn Foo: !Sized));
// Wrappers around unsized types are also unsized themselves.
struct Bar([u8]);
assert!(impls!(Bar: !Sized));
```
### Generic Types
When called from a generic function, the returned value is based on the
constraints of the generic type:
```rust
use std::cell::Cell;
struct Value {
// ...
}
impl Value {
fn do_stuff() {
assert!(impls!(Cell: Send));
// ...
}
}
```
Keep in mind that this can result in false negatives:
```rust
const fn is_copy() -> bool {
impls!(T: Copy)
}
assert_ne!(is_copy::(), impls!(u32: Copy));
```
[precedence]: https://doc.rust-lang.org/reference/expressions.html#expression-precedence
[`static_assertions`]: https://docs.rs/static_assertions
### Lifetimes
Traits with lifetimes are also supported:
```rust
trait Ref<'a> {}
impl<'a, T: ?Sized> Ref<'a> for &'a T {}
impl<'a, T: ?Sized> Ref<'a> for &'a mut T {}
assert!(impls!(&'static str: Ref<'static>));
assert!(impls!(&'static mut [u8]: Ref<'static>));
assert!(impls!(String: !Ref<'static>));
```
### Trait-Dependent Type Sizes
This macro enables something really cool (read cursed) that couldn't be done
before: making a type's size dependent on what traits it implements! Note that
this probably is a bad idea and shouldn't be used in production.
Here `Foo` becomes 32 bytes for no other reason than it implementing [`Clone`]:
```rust
const SIZE: usize = 32 * (impls!(Foo: Clone) as usize);
#[derive(Clone)]
struct Foo([u8; SIZE]);
assert_eq!(std::mem::size_of::(), 32);
```
The [`bool`] returned from [`impls!`] gets casted to a [`usize`], becoming 1 or
0 depending on if it's `true` or `false` respectively. If `true`, this becomes
32 × 1, which is 32. This then becomes the length of the byte array in `Foo`.
## Authors
- Nikolai Vazquez
(GitHub: [@nvzqz](https://github.com/nvzqz), Twitter: [@NikolaiVazquez])
Implemented the `impls!` macro with support for all logical operators and
without the limitations of the initial `does_impl!` macro by Nadrieril.
- Nadrieril Feneanar
(GitHub: [@Nadrieril](https://github.com/Nadrieril))
Implemented the initial `does_impl!` macro in
[nvzqz/static-assertions-rs#28](https://github.com/nvzqz/static-assertions-rs/pull/28)
upon which this crate was originally based.
## License
This project is released under either:
- [MIT License](https://github.com/nvzqz/impls/blob/master/LICENSE-MIT)
- [Apache License (Version 2.0)](https://github.com/nvzqz/impls/blob/master/LICENSE-APACHE)
at your choosing.
[@NikolaiVazquez]: https://twitter.com/NikolaiVazquez
[compile-time]: https://en.wikipedia.org/wiki/Compile_time
[`&mut T`]: https://doc.rust-lang.org/std/primitive.reference.html
[`bool`]: https://doc.rust-lang.org/std/primitive.bool.html
[`Clone`]: https://doc.rust-lang.org/std/clone/trait.Clone.html
[`Copy`]: https://doc.rust-lang.org/std/marker/trait.Copy.html
[`Sized`]: https://doc.rust-lang.org/std/marker/trait.Sized.html
[`usize`]: https://doc.rust-lang.org/std/primitive.usize.html
[`Cargo.toml`]: https://doc.rust-lang.org/cargo/reference/manifest.html
[`impls!`]: https://docs.rs/impls/1.0.3/impls/macro.impls.html
[2018]: https://blog.rust-lang.org/2018/12/06/Rust-1.31-and-rust-2018.html#rust-2018
[crate]: https://crates.io/crates/impls
[`BitAnd`]: https://doc.rust-lang.org/std/ops/trait.BitAnd.html
[`BitOr`]: https://doc.rust-lang.org/std/ops/trait.BitOr.html
[`BitXor`]: https://doc.rust-lang.org/std/ops/trait.BitXor.html
[`Into`]: https://doc.rust-lang.org/std/convert/trait.Into.html
[`Not`]: https://doc.rust-lang.org/std/ops/trait.Not.html
[`Send`]: https://doc.rust-lang.org/std/marker/trait.Send.html
[`Sync`]: https://doc.rust-lang.org/std/marker/trait.Send.html
[ptr]: https://doc.rust-lang.org/std/primitive.pointer.html
[AST]: https://en.wikipedia.org/wiki/Abstract_syntax_tree
[exclusive disjunction]: https://en.wikipedia.org/wiki/Exclusive_disjunction
[logical conjunction]: https://en.wikipedia.org/wiki/Logical_conjunction
[logical disjunction]: https://en.wikipedia.org/wiki/Logical_disjunction
impls-1.0.3/src/lib.rs 0100644 0000765 0000024 00000061167 13602702455 0013000 0 ustar 00 0000000 0000000 //!
//!
//!
//! Determine if a type implements a logical trait
//! expression[**?**](#logical-trait-expression), brought to you by
//! [@NikolaiVazquez]!
//!
//! This library defines [`impls!`], a macro[**?**](#macro) that
//! returns a [`bool`] indicating whether a type implements a boolean-like
//! expression over a set of traits[**?**](#trait).
//!
//! ```
//! # #[macro_use] extern crate impls;
//! assert!(impls!(String: Clone & !Copy & Send & Sync));
//! ```
//!
//! See ["Examples"](#examples) for detailed use cases and, if you're brave, see
//! ["Trait-Dependent Type Sizes"](#trait-dependent-type-sizes) for some cursed
//! code.
//!
//! # Index
//!
//! - [Reasoning](#reasoning)
//! - [Usage](#usage)
//! - [Vocabulary](#vocabulary)
//! - [Macro](#macro)
//! - [Trait](#trait)
//! - [Logical Trait Expression](#logical-trait-expression)
//! - [Examples](#examples)
//! - [Constant Evaluation](#constant-evaluation)
//! - [Precedence and Nesting](#precedence-and-nesting)
//! - [Mutual Exclusion](#mutual-exclusion)
//! - [Reference Types](#reference-types)
//! - [Unsized Types](#unsized-types)
//! - [Generic Types](#generic-types)
//! - [Lifetimes](#lifetimes)
//! - [Trait-Dependent Type Sizes](#trait-dependent-type-sizes)
//! - [Authors](#authors)
//! - [License](#license)
//!
//! # Reasoning
//!
//! As a library author, it's important to ensure that your API remains stable.
//! Trait implementations are part of API stability. For example: if you
//! accidentally introduce an inner type that makes your publicly-exposed type
//! no longer be [`Send`] or [`Sync`], you've now broken your API without
//! noticing it! The most common case of this happening is adding a [raw
//! pointer][ptr] (i.e. `*const T`, `*mut T`) as a type field.
//!
//! By checking situations like this with [`impls!`], either at [compile-time]
//! or in a unit test, you can ensure that no API-breaking changes are made
//! without noticing until it's too late.
//!
//! # Usage
//!
//! This crate is available [on crates.io][crate] and can be used by adding the
//! following to your project's [`Cargo.toml`]:
//!
//! ```toml
//! [dependencies]
//! impls = "1"
//! ```
//!
//! and this to your crate root (`main.rs` or `lib.rs`):
//!
//! ```
//! # #[allow(unused_imports)]
//! #[macro_use]
//! extern crate impls;
//! # fn main() {}
//! ```
//!
//! When using [Rust 2018 edition][2018], the following import can help if
//! having `#[macro_use]` is undesirable.
//!
//! ```edition2018
//! use impls::impls;
//! ```
//!
//! # Vocabulary
//!
//! This documentation uses jargon that may be new to inexperienced Rust users.
//! This section exists to make these terms easier to understand. Feel free to
//! skip this section if these are already familiar to you.
//!
//! ## Macro
//!
//! In Rust, macros are functions over the [abstract syntax tree (AST)][AST].
//! They map input tokens to output tokens by performing some operation over
//! them through a set of rules. Because of this, only their outputs are ever
//! type-checked.
//!
//! If you wish to learn about implementing macros, I recommend:
//! - [The Little Book of Rust Macros](https://danielkeep.github.io/tlborm/book/index.html)
//! - ["Macros" - The Rust Programming Language](https://doc.rust-lang.org/book/ch19-06-macros.html)
//! - ["Macros" - The Rust Reference](https://doc.rust-lang.org/stable/reference/macros.html)
//! - ["Macros By Example" - The Rust Reference](https://doc.rust-lang.org/stable/reference/macros-by-example.html)
//!
//! To use this crate, you do not need to know how macros are defined.
//!
//! ## Trait
//!
//! In Rust, traits are a way of defining a generalized property. They should be
//! thought of expressing what a type is capable of doing. For example: if a
//! type implements [`Into`] for some type `T`, then we know it can be converted
//! into `T` by just calling the `.into()` method on it.
//!
//! If you wish to learn about traits in detail, I recommend:
//! - ["Traits: Defining Shared Behavior" - The Rust Programming Language](https://doc.rust-lang.org/book/ch10-02-traits.html)
//! - ["Traits" - The Rust Reference](https://doc.rust-lang.org/stable/reference/items/traits.html)
//!
//! ## Logical Trait Expression
//!
//! In this crate, traits should be thought of as [`bool`]s where the condition
//! is whether the given type implements the trait or not.
//!
//! An expression can be formed from these trait operations:
//!
//! - And (`&`): also known as [logical conjunction], this returns `true` if
//! **both** operands are `true`. This is usually defined in Rust via the
//! [`BitAnd`] trait.
//!
//! - Or (`|`): also known as [logical disjunction], this returns `true` if
//! **either** of two operands is `true`. This is usually defined in Rust via
//! the [`BitOr`] trait.
//!
//! - Exclusive-or (`^`): also known as [exclusive disjunction], this returns
//! `true` if **only one** of two operands is `true`. This is usually defined
//! in Rust via the [`BitXor`] trait.
//!
//! - Not (`!`): a negation that returns `false` if the operand is `true`, or
//! `true` if the operand is `false`. This is usually defined in Rust via the
//! [`Not`] trait.
//!
//! See ["Precedence and Nesting"](#precedence-and-nesting) for information
//! about the order in which these operations are performed.
//!
// IMPORTANT: These examples are copy and pasted directly from `impls!`
//! # Examples
//!
//! This macro works in every type context. See below for use cases.
//!
//! ## Constant Evaluation
//!
//! Because types are [compile-time] constructs, the result of this macro can be
//! used as a `const` value:
//!
//! ```
//! # #[macro_use] extern crate impls;
//! const IMPLS: bool = impls!(u8: From);
//! ```
//!
//! Using [`static_assertions`], we can fail to compile if the trait expression
//! evaluates to `false`:
//!
//! ```compile_fail
//! # #[macro_use] extern crate impls;
//! # macro_rules! const_assert {
//! # ($x:expr) => { let _: [(); 1] = [(); $x as usize]; }
//! # }
//! const_assert!(impls!(*const u8: Send | Sync));
//! ```
//!
//! ## Precedence and Nesting
//!
//! Trait operations abide by [Rust's expression precedence][precedence]. To
//! define a custom order of operations (e.g. left-to-right), simply nest the
//! expressions with parentheses.
//!
//! ```
//! # #[macro_use] extern crate impls;
//! let pre = impls!(u64: From | From ^ From & From);
//! let ltr = impls!(u64: ((From | From) ^ From) & From);
//!
//! assert_eq!(pre, true | true ^ true & true);
//! assert_ne!(pre, ltr);
//! ```
//!
//! ## Mutual Exclusion
//!
//! Because exclusive-or (`^`) is a trait operation, we can check that a type
//! implements one of two traits, but not both:
//!
//! ```
//! # #[macro_use] extern crate impls;
//! struct T;
//!
//! trait Foo {}
//! trait Bar {}
//!
//! impl Foo for T {}
//!
//! assert!(impls!(T: Foo ^ Bar));
//! ```
//!
//! ## Reference Types
//!
//! Something that's surprising to many Rust users is that [`&mut T`] _does not_
//! implement [`Copy`] _nor_ [`Clone`]:
//!
//! ```
//! # #[macro_use] extern crate impls;
//! assert!(impls!(&mut u32: !Copy & !Clone));
//! ```
//!
//! Surely you're thinking now that this macro must be broken, because you've
//! been able to reuse `&mut T` throughout your lifetime with Rust. This works
//! because, in certain contexts, the compiler silently adds "re-borrows"
//! (`&mut *ref`) with a shorter lifetime and shadows the original. In reality,
//! `&mut T` is a move-only type.
//!
//! ## Unsized Types
//!
//! There's a variety of types in Rust that don't implement [`Sized`]:
//!
//! ```
//! # #[macro_use] extern crate impls;
//! // Slices store their size with their pointer.
//! assert!(impls!(str: !Sized));
//! assert!(impls!([u8]: !Sized));
//!
//! // Trait objects store their size in a vtable.
//! trait Foo {}
//! assert!(impls!(dyn Foo: !Sized));
//!
//! // Wrappers around unsized types are also unsized themselves.
//! struct Bar([u8]);
//! assert!(impls!(Bar: !Sized));
//! ```
//!
//! ## Generic Types
//!
//! When called from a generic function, the returned value is based on the
//! constraints of the generic type:
//!
//! ```
//! # #[macro_use] extern crate impls;
//! use std::cell::Cell;
//!
//! struct Value {
//! // ...
//! # value: T
//! }
//!
//! impl Value {
//! fn do_stuff() {
//! assert!(impls!(Cell: Send));
//! // ...
//! }
//! }
//! ```
//!
//! Keep in mind that this can result in false negatives:
//!
//! ```
//! # #[macro_use] extern crate impls;
//! const fn is_copy() -> bool {
//! impls!(T: Copy)
//! }
//!
//! assert_ne!(is_copy::(), impls!(u32: Copy));
//! ```
//!
//! [precedence]: https://doc.rust-lang.org/reference/expressions.html#expression-precedence
//! [`static_assertions`]: https://docs.rs/static_assertions
//!
//! ## Lifetimes
//!
//! Traits with lifetimes are also supported:
//!
//! ```
//! # #[macro_use] extern crate impls;
//! trait Ref<'a> {}
//! impl<'a, T: ?Sized> Ref<'a> for &'a T {}
//! impl<'a, T: ?Sized> Ref<'a> for &'a mut T {}
//!
//! assert!(impls!(&'static str: Ref<'static>));
//! assert!(impls!(&'static mut [u8]: Ref<'static>));
//! assert!(impls!(String: !Ref<'static>));
//! ```
//!
//! ## Trait-Dependent Type Sizes
//!
//! This macro enables something really cool (read cursed) that couldn't be done
//! before: making a type's size dependent on what traits it implements! Note
//! that this probably is a bad idea and shouldn't be used in production.
//!
//! Here `Foo` becomes 32 bytes for no other reason than it implementing
//! [`Clone`]:
//!
//! ```
//! # #[macro_use] extern crate impls;
//! const SIZE: usize = 32 * (impls!(Foo: Clone) as usize);
//!
//! #[derive(Clone)]
//! struct Foo([u8; SIZE]);
//!
//! assert_eq!(std::mem::size_of::(), 32);
//! ```
//!
//! The [`bool`] returned from [`impls!`] gets casted to a [`usize`], becoming 1
//! or 0 depending on if it's `true` or `false` respectively. If `true`, this
//! becomes 32 × 1, which is 32. This then becomes the length of the byte array
//! in `Foo`.
//!
//! # Authors
//!
//! - Nikolai Vazquez
//! (GitHub: [@nvzqz](https://github.com/nvzqz), Twitter: [@NikolaiVazquez])
//!
//! Implemented the `impls!` macro with support for all logical operators and
//! without the limitations of the initial `does_impl!` macro by Nadrieril.
//!
//! - Nadrieril Feneanar
//! (GitHub: [@Nadrieril](https://github.com/Nadrieril))
//!
//! Implemented the initial `does_impl!` macro in
//! [nvzqz/static-assertions-rs#28](https://github.com/nvzqz/static-assertions-rs/pull/28)
//! upon which this crate was originally based.
//!
//! # License
//!
//! This project is released under either:
//!
//! - [MIT License](https://github.com/nvzqz/impls/blob/master/LICENSE-MIT)
//! - [Apache License (Version 2.0)](https://github.com/nvzqz/impls/blob/master/LICENSE-APACHE)
//!
//! at your choosing.
//!
//! [@NikolaiVazquez]: https://twitter.com/NikolaiVazquez
//!
//! [compile-time]: https://en.wikipedia.org/wiki/Compile_time
//!
//! [`&mut T`]: https://doc.rust-lang.org/std/primitive.reference.html
//! [`bool`]: https://doc.rust-lang.org/std/primitive.bool.html
//! [`Clone`]: https://doc.rust-lang.org/std/clone/trait.Clone.html
//! [`Copy`]: https://doc.rust-lang.org/std/marker/trait.Copy.html
//! [`Sized`]: https://doc.rust-lang.org/std/marker/trait.Sized.html
//! [`usize`]: https://doc.rust-lang.org/std/primitive.usize.html
//!
//! [`Cargo.toml`]: https://doc.rust-lang.org/cargo/reference/manifest.html
//! [`impls!`]: macro.impls.html
//! [2018]: https://blog.rust-lang.org/2018/12/06/Rust-1.31-and-rust-2018.html#rust-2018
//! [crate]: https://crates.io/crates/impls
//!
//! [`BitAnd`]: https://doc.rust-lang.org/std/ops/trait.BitAnd.html
//! [`BitOr`]: https://doc.rust-lang.org/std/ops/trait.BitOr.html
//! [`BitXor`]: https://doc.rust-lang.org/std/ops/trait.BitXor.html
//! [`Into`]: https://doc.rust-lang.org/std/convert/trait.Into.html
//! [`Not`]: https://doc.rust-lang.org/std/ops/trait.Not.html
//! [`Send`]: https://doc.rust-lang.org/std/marker/trait.Send.html
//! [`Sync`]: https://doc.rust-lang.org/std/marker/trait.Send.html
//! [ptr]: https://doc.rust-lang.org/std/primitive.pointer.html
//!
//! [AST]: https://en.wikipedia.org/wiki/Abstract_syntax_tree
//! [exclusive disjunction]: https://en.wikipedia.org/wiki/Exclusive_disjunction
//! [logical conjunction]: https://en.wikipedia.org/wiki/Logical_conjunction
//! [logical disjunction]: https://en.wikipedia.org/wiki/Logical_disjunction
#![deny(missing_docs)]
#![doc(
html_root_url = "https://docs.rs/impls/1.0.3",
html_logo_url = "https://raw.githubusercontent.com/nvzqz/impls/assets/logo.svg?sanitize=true"
)]
// Allocating types like `String` are used when testing.
#![cfg_attr(not(test), no_std)]
#[doc(hidden)]
pub extern crate core as _core;
/// Returns `true` if a type implements a logical trait expression.
///
// IMPORTANT: Update crate level docs when updating these examples!
/// # Examples
///
/// This macro works in every type context. See below for use cases.
///
/// ## Constant Evaluation
///
/// Because types are [compile-time] constructs, the result of this macro can be
/// used as a `const` value:
///
/// ```
/// # #[macro_use] extern crate impls;
/// const IMPLS: bool = impls!(u8: From);
/// ```
///
/// Using [`static_assertions`], we can fail to compile if the trait expression
/// evaluates to `false`:
///
/// ```compile_fail
/// # #[macro_use] extern crate impls;
/// # macro_rules! const_assert {
/// # ($x:expr) => { let _: [(); 1] = [(); $x as usize]; }
/// # }
/// const_assert!(impls!(*const u8: Send | Sync));
/// ```
///
/// ## Precedence and Nesting
///
/// Trait operations abide by [Rust's expression precedence][precedence]. To
/// define a custom order of operations (e.g. left-to-right), simply nest the
/// expressions with parentheses.
///
/// ```
/// # #[macro_use] extern crate impls;
/// let pre = impls!(u64: From | From ^ From & From);
/// let ltr = impls!(u64: ((From | From) ^ From) & From);
///
/// assert_eq!(pre, true | true ^ true & true);
/// assert_ne!(pre, ltr);
/// ```
///
/// ## Mutual Exclusion
///
/// Because exclusive-or (`^`) is a trait operation, we can check that a type
/// implements one of two traits, but not both:
///
/// ```
/// # #[macro_use] extern crate impls;
/// struct T;
///
/// trait Foo {}
/// trait Bar {}
///
/// impl Foo for T {}
///
/// assert!(impls!(T: Foo ^ Bar));
/// ```
///
/// ## Reference Types
///
/// Something that's surprising to many Rust users is that [`&mut T`] _does not_
/// implement [`Copy`] _nor_ [`Clone`]:
///
/// ```
/// # #[macro_use] extern crate impls;
/// assert!(impls!(&mut u32: !Copy & !Clone));
/// ```
///
/// Surely you're thinking now that this macro must be broken, because you've
/// been able to reuse `&mut T` throughout your lifetime with Rust. This works
/// because, in certain contexts, the compiler silently adds "re-borrows"
/// (`&mut *ref`) with a shorter lifetime and shadows the original. In reality,
/// `&mut T` is a move-only type.
///
/// ## Unsized Types
///
/// There's a variety of types in Rust that don't implement [`Sized`]:
///
/// ```
/// # #[macro_use] extern crate impls;
/// // Slices store their size with their pointer.
/// assert!(impls!(str: !Sized));
/// assert!(impls!([u8]: !Sized));
///
/// // Trait objects store their size in a vtable.
/// trait Foo {}
/// assert!(impls!(dyn Foo: !Sized));
///
/// // Wrappers around unsized types are also unsized themselves.
/// struct Bar([u8]);
/// assert!(impls!(Bar: !Sized));
/// ```
///
/// ## Generic Types
///
/// When called from a generic function, the returned value is based on the
/// constraints of the generic type:
///
/// ```
/// # #[macro_use] extern crate impls;
/// use std::cell::Cell;
///
/// struct Value {
/// // ...
/// # value: T
/// }
///
/// impl Value {
/// fn do_stuff() {
/// assert!(impls!(Cell: Send));
/// // ...
/// }
/// }
/// ```
///
/// Keep in mind that this can result in false negatives:
///
/// ```
/// # #[macro_use] extern crate impls;
/// const fn is_copy() -> bool {
/// impls!(T: Copy)
/// }
///
/// assert_ne!(is_copy::(), impls!(u32: Copy));
/// ```
///
/// [precedence]: https://doc.rust-lang.org/reference/expressions.html#expression-precedence
/// [`static_assertions`]: https://docs.rs/static_assertions
///
/// ## Lifetimes
///
/// Traits with lifetimes are also supported:
///
/// ```
/// # #[macro_use] extern crate impls;
/// trait Ref<'a> {}
/// impl<'a, T: ?Sized> Ref<'a> for &'a T {}
/// impl<'a, T: ?Sized> Ref<'a> for &'a mut T {}
///
/// assert!(impls!(&'static str: Ref<'static>));
/// assert!(impls!(&'static mut [u8]: Ref<'static>));
/// assert!(impls!(String: !Ref<'static>));
/// ```
///
/// ## Trait-Dependent Type Sizes
///
/// This macro enables something really cool (read cursed) that couldn't be done
/// before: making a type's size dependent on what traits it implements! Note
/// that this probably is a bad idea and shouldn't be used in production.
///
/// Here `Foo` becomes 32 bytes for no other reason than it implementing
/// [`Clone`]:
///
/// ```
/// # #[macro_use] extern crate impls;
/// const SIZE: usize = 32 * (impls!(Foo: Clone) as usize);
///
/// #[derive(Clone)]
/// struct Foo([u8; SIZE]);
///
/// assert_eq!(std::mem::size_of::(), 32);
/// ```
///
/// The [`bool`] returned from `impls!` gets casted to a [`usize`], becoming 1
/// or 0 depending on if it's `true` or `false` respectively. If `true`, this
/// becomes 32 × 1, which is 32. This then becomes the length of the byte array
/// in `Foo`.
///
/// [compile-time]: https://en.wikipedia.org/wiki/Compile_time
///
/// [`&mut T`]: https://doc.rust-lang.org/std/primitive.reference.html
/// [`bool`]: https://doc.rust-lang.org/std/primitive.bool.html
/// [`Clone`]: https://doc.rust-lang.org/std/clone/trait.Clone.html
/// [`Copy`]: https://doc.rust-lang.org/std/marker/trait.Copy.html
/// [`Sized`]: https://doc.rust-lang.org/std/marker/trait.Sized.html
/// [`usize`]: https://doc.rust-lang.org/std/primitive.usize.html
#[macro_export(local_inner_macros)]
macro_rules! impls {
($type:ty: $($trait_expr:tt)+) => {
_impls!($type: $($trait_expr)+)
};
}
/// Handles the dirty work of `impls`.
#[doc(hidden)]
#[macro_export(local_inner_macros)]
macro_rules! _impls {
// ONE: Turn `$trait` into `true` or `false` based on whether `$type`
// implements it.
($type:ty: $(! !)* $trait:path) => {{
// Do not import types in order to prevent trait name collisions.
/// Fallback trait with `False` for `IMPLS` if the type does not
/// implement the given trait.
trait DoesNotImpl {
const IMPLS: bool = false;
}
impl DoesNotImpl for T {}
/// Concrete type with `True` for `IMPLS` if the type implements the
/// given trait. Otherwise, it falls back to `DoesNotImpl`.
struct Wrapper($crate::_core::marker::PhantomData);
#[allow(dead_code)]
impl Wrapper {
const IMPLS: bool = true;
}
>::IMPLS
}};
// NOT
($type:ty: $(! !)* !$trait:path) => {
!_impls!($type: $trait)
};
// PAREN
($type:ty: $(! !)* ($($trait_expr:tt)+)) => {
_impls!($type: $($trait_expr)+)
};
// PAREN+NOT
($type:ty: $(! !)* !($($trait_expr:tt)+)) => {
!_impls!($type: $($trait_expr)+)
};
// PAREN+OR
($type:ty: $(! !)* ($($t1:tt)+) | $($t2:tt)+) => {
_impls!($type: $($t1)+)
|
_impls!($type: $($t2)+)
};
// PAREN+OR+NOT
($type:ty: $(! !)* !($($t1:tt)+) | $($t2:tt)+) => {
!_impls!($type: $($t1)+)
|
_impls!($type: $($t2)+)
};
// PAREN+AND
($type:ty: $(! !)* ($($t1:tt)+) & $($t2:tt)+) => {
_impls!($type: $($t1)+)
&
_impls!($type: $($t2)+)
};
// PAREN+AND+NOT
($type:ty: $(! !)* !($($t1:tt)+) & $($t2:tt)+) => {
!_impls!($type: $($t1)+)
&
_impls!($type: $($t2)+)
};
// PAREN+XOR
($type:ty: $(! !)* ($($t1:tt)+) ^ $($t2:tt)+) => {
_impls!($type: $($t1)+)
^
_impls!($type: $($t2)+)
};
// PAREN+XOR+NOT
($type:ty: $(! !)* !($($t1:tt)+) ^ $($t2:tt)+) => {
!_impls!($type: $($t1)+)
^
_impls!($type: $($t2)+)
};
// OR: Any.
($type:ty: $(! !)* $t1:path | $($t2:tt)+) => {{
_impls!($type: $t1)
|
_impls!($type: $($t2)+)
}};
// OR+NOT: Any.
($type:ty: $(! !)* !$t1:path | $($t2:tt)+) => {{
!_impls!($type: $t1)
|
_impls!($type: $($t2)+)
}};
// AND: 0 lifetimes, 0 generics.
($type:ty: $(! !)* $t1:ident & $($t2:tt)+) => {{
_impls!($type: $t1)
&
_impls!($type: $($t2)+)
}};
// AND+NOT: 0 lifetimes, 0 generics.
($type:ty: $(! !)* !$t1:ident & $($t2:tt)+) => {{
!_impls!($type: $t1)
&
_impls!($type: $($t2)+)
}};
// AND: 1+ lifetimes, 0+ generics.
(
$type:ty: $(! !)*
$t1:ident < $($t1_lifetime:lifetime),+ $(, $t1_generic:ty)* $(,)? >
&
$($t2:tt)+
) => {{
_impls!($type: $t1 < $($t1_lifetime),+ $(, $t1_generic)* >)
&
_impls!($type: $($t2)+)
}};
// AND+NOT: 1+ lifetimes, 0+ generics.
(
$type:ty: $(! !)*
!$t1:ident < $($t1_lifetime:lifetime),+ $(, $t1_generic:ty)* $(,)? >
&
$($t2:tt)+
) => {{
!_impls!($type: $t1 < $($t1_lifetime),+ $(, $t1_generic)* >)
&
_impls!($type: $($t2)+)
}};
// AND: 0 lifetimes, 1+ generics.
(
$type:ty: $(! !)*
$t1:ident < $($t1_generic:ty),+ $(,)? >
&
$($t2:tt)+
) => {{
_impls!($type: $t1 < $($t1_generic),+ >)
&
_impls!($type: $($t2)+)
}};
// AND+NOT: 0 lifetimes, 1+ generics.
(
$type:ty: $(! !)*
!$t1:ident < $($t1_generic:ty),+ $(,)? >
&
$($t2:tt)+
) => {{
!_impls!($type: $t1 < $($t1_generic),+ >)
&
_impls!($type: $($t2)+)
}};
// XOR: 0 lifetimes, 0 generics.
($type:ty: $(! !)* $t1:ident ^ $($t2:tt)+) => {{
_impls!($type: $t1)
^
_impls!($type: $($t2)+)
}};
// XOR+NOT: 0 lifetimes, 0 generics.
($type:ty: $(! !)* !$t1:ident ^ $($t2:tt)+) => {{
! _impls!($type: $t1)
^
_impls!($type: $($t2)+)
}};
// XOR: 1+ lifetimes, 0+ generics.
(
$type:ty: $(! !)*
$t1:ident < $($t1_lifetime:lifetime),+ $(, $t1_generic:ty)* $(,)? >
^
$($t2:tt)+
) => {{
_impls!($type: $t1 < $($t1_lifetime),+ $(, $t1_generic)* >)
^
_impls!($type: $($t2)+)
}};
// XOR+NOT: 1+ lifetimes, 0+ generics.
(
$type:ty: $(! !)*
! $t1:ident < $($t1_lifetime:lifetime),+ $(, $t1_generic:ty)* $(,)? >
^
$($t2:tt)+
) => {{
!_impls!($type: $t1 < $($t1_lifetime),+ $(, $t1_generic)* >)
^
_impls!($type: $($t2)+)
}};
// XOR: 0 lifetimes, 1+ generics.
(
$type:ty: $(! !)*
$t1:ident < $($t1_generic:ty),+ $(,)? >
^
$($t2:tt)+
) => {{
_impls!($type: $t1 < $($t1_generic),+ >)
^
_impls!($type: $($t2)+)
}};
// XOR+NOT: 0 lifetimes, 1+ generics.
(
$type:ty: $(! !)*
! $t1:ident < $($t1_generic:ty),+ $(,)? >
^
$($t2:tt)+
) => {{
! _impls!($type: $t1 < $($t1_generic),+ >)
^
_impls!($type: $($t2)+)
}};
}
// Declare after macros in order to be able to use them.
#[cfg(test)]
mod tests;
impls-1.0.3/src/tests/bool.rs 0100644 0000765 0000024 00000000267 13602564703 0014323 0 ustar 00 0000000 0000000 pub struct True;
pub struct False;
impl True {
pub const fn value(self) -> bool {
true
}
}
impl False {
pub const fn value(self) -> bool {
false
}
}
impls-1.0.3/src/tests/mod.rs 0100644 0000765 0000024 00000005173 13602564703 0014150 0 ustar 00 0000000 0000000 #![allow(dead_code)]
mod bool;
#[derive(Clone)]
struct Test;
#[derive(Clone)]
struct Box(T);
trait True {}
impl True for T {}
trait False {}
// Tests that `impls!` follows Rust's rules of precedence.
//
// Rust's rules of precedence are defined at:
// https://doc.rust-lang.org/reference/expressions.html#expression-precedence
#[test]
fn precedence() {
macro_rules! table {
($($a:ident, $b:ident, $c:ident, $d:ident;)+) => { $({
const IMPLS: bool = bool::$a.value() | bool::$b.value() ^ bool::$c.value() & bool::$d.value();
assert_eq!(impls!(Test: $a | $b ^ $c & $d), IMPLS);
assert_eq!(impls!(Test: $a | ($b ^ ($c & $d))), IMPLS);
assert_ne!(impls!(Test: (($a | $b) ^ $c) & $d), IMPLS);
})+ };
}
// Table of cases where left-to-right parsing differs from precedence rules.
//
// https://play.rust-lang.org/?gist=7cbed02c68422f9464d0df79d39e99b0
#[rustfmt::skip]
table! {
False, True, False, False;
False, True, True, False;
True, False, False, False;
True, False, True, False;
True, False, True, True;
True, True, False, False;
True, True, True, False;
True, True, True, True;
}
}
#[test]
fn impls() {
let mut errors = String::new();
macro_rules! assert_impl {
($t:ty: $($trait_expr:tt)+) => {
if !impls!($t: $($trait_expr)+) {
errors.push_str(&format!(
"[{file}:{line}] {ty}: {expr}\n",
file = file!(),
line = line!(),
ty = stringify!($t),
expr = stringify!($($trait_expr)+)
));
}
};
}
assert_impl!(u8: (From) | (Into));
assert_impl!((): (From) | (From) | Send);
assert_impl!((): (!From) & !(From) & Send);
assert_impl!((): Copy | Clone);
assert_impl!((): Copy & Clone);
assert_impl!((): !(Copy ^ Clone));
assert_impl!(Test: Copy | Clone);
assert_impl!(Test: !Copy | Clone);
assert_impl!(Test: !Copy & Clone);
assert_impl!(Test: !Copy & (Clone));
assert_impl!(Test: !(Copy) & Clone);
assert_impl!(Test: !(!Clone));
assert_impl!(Test: !(Copy) & !(!Clone));
assert_impl!(Test: !(Copy & Clone));
assert_impl!(str: !Copy & !Clone);
assert_impl!(Box: Clone);
assert_impl!(Box: Clone & Send);
assert_impl!(Box: !(From | Into));
assert_impl!(&mut u8: !Copy);
if !errors.is_empty() {
panic!("Failed to satisfy implementations:\n{}", errors);
}
}
impls-1.0.3/.cargo_vcs_info.json 0000644 00000000112 13602702504 0012250 0 ustar 00 {
"git": {
"sha1": "a8f3599bd2f560f66dbe21047f33937420b67090"
}
}
