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//! `whiteout` provides macros that erase the type of any value into
//! an `impl Trait` for a given trait.
//!
//! # Examples
//!
//! Single values can be erased using the `erase!` macro.
//!
//! ```
//!# #[macro_use]
//!# extern crate whiteout;
//!# fn main() {
//! let a = erase!(10, std::ops::Add<i64, Output=i64>);
//! let b = erase!(5, std::ops::Add<i64, Output=i64>);
//! assert_eq!(a + 10, 20);
//! assert_eq!(b + 10, 15);
//! // This fails, the types are opaque
//! // assert_eq!(a + b, 15);
//!# }
//! ```
//!
//! These erased values can't be used together, though; they have different
//! anonymized types. Therefore, you sometimes need the `eraser!` macro.
//!
//! ```
//! #[macro_use]
//! extern crate whiteout;
//!
//! // Define a custom trait into which types will be erased.
//! trait MyTrait:
//! std::ops::Add<Self, Output=Self> // Allow the operation we need
//! + std::convert::From<i32> // Allow converting from concrete values
//! + std::fmt::Debug // Allow printing (for use with assert!())
//! + PartialEq // Allow comparison (for use with assert_eq!())
//! {}
//!
//! // Implement MyTrait for all possible types.
//! impl<T> MyTrait for T
//! where T: std::ops::Add<Self, Output=Self>
//! + std::convert::From<i32>
//! + std::fmt::Debug
//! + PartialEq
//! {}
//!
//! // Create an eraser function for the custom trait
//! eraser!(erase_my_trait, MyTrait);
//!
//! fn main() {
//! // Use the eraser function.
//! // If we used erase!(10, MyTrait); for these
//! // they would be of different types.
//! let a = erase_my_trait(10);
//! let b = erase_my_trait(5);
//! assert_eq!(a + b, 15.into());
//! }
//! ```
//!
//!
/// `eraser!(name, trait)` creates a function with the given identifier that
/// erases values to an anonymous type that is `impl Trait` for the given trait.
///
/// # Examples
///
/// ```
/// #[macro_use]
/// extern crate whiteout;
///
/// // Define a custom trait into which types will be erased.
/// trait MyTrait:
/// std::ops::Add<Self, Output=Self> // Allow the operation we need
/// + std::convert::From<i32> // Allow converting from concrete values
/// + std::fmt::Debug // Allow printing (for use with assert!())
/// + PartialEq // Allow comparison (for use with assert_eq!())
/// {}
///
/// // Implement MyTrait for all possible types.
/// impl<T> MyTrait for T
/// where T: std::ops::Add<Self, Output=Self>
/// + std::convert::From<i32>
/// + std::fmt::Debug
/// + PartialEq
/// {}
///
/// // Create an eraser function for the custom trait
/// eraser!(erase_my_trait, MyTrait);
///
/// fn main() {
/// // Use the eraser function.
/// // If we used erase!(10, MyTrait); for these
/// // they would be of different types.
/// let a = erase_my_trait(10);
/// let b = erase_my_trait(5);
/// assert_eq!(a + b, 15.into());
/// }
/// ```
///
///
/// `erase!(value, trait)` turns a value of any type that implements trait into
/// an erasted type which is `impl Trait` for that trait.
///
/// # Examples
///
///
/// ```
///# #[macro_use]
///# extern crate whiteout;
///# fn main() {
/// let a = erase!(10, std::ops::Add<i64, Output=i64>);
/// let b = erase!(5, std::ops::Add<i64, Output=i64>);
/// assert_eq!(a + 10, 20);
/// assert_eq!(b + 10, 15);
/// // This fails, the types are opaque
/// // assert_eq!(a + b, 15);
///# }
/// ```
///