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//! Macro for static assert that types implement a trait or not. //! //! Note: this macro can only be used inside function body due to //! restriction of Rust. //! //! # Example //! //! Assuming you have the following definitions: //! ``` //! struct C; //! struct Java; //! struct JavaScript; //! struct Python; //! struct Rust; //! //! trait StaticTyping {} //! impl StaticTyping for C {} //! impl StaticTyping for Java {} //! impl StaticTyping for Rust {} //! ``` //! //! This should build: //! ``` //! # #[macro_use] extern crate assert_impl; //! # struct C; //! # struct Java; //! # struct JavaScript; //! # struct Python; //! # struct Rust; //! # trait StaticTyping {} //! # impl StaticTyping for C {} //! # impl StaticTyping for Java {} //! # impl StaticTyping for Rust {} //! assert_impl!(StaticTyping: C, Java, Rust); //! assert_impl!(!StaticTyping: JavaScript, Python); //! ``` //! //! But these should fail to build: //! ```compile_fail //! # #[macro_use] extern crate assert_impl; //! # struct C; //! # struct Java; //! # struct JavaScript; //! # struct Python; //! # struct Rust; //! # trait StaticTyping {} //! # impl StaticTyping for C {} //! # impl StaticTyping for Java {} //! # impl StaticTyping for Rust {} //! assert_impl!(StaticTyping: JavaScript); //! ``` //! //! ```compile_fail //! # #[macro_use] extern crate assert_impl; //! # struct C; //! # struct Java; //! # struct JavaScript; //! # struct Python; //! # struct Rust; //! # trait StaticTyping {} //! # impl StaticTyping for C {} //! # impl StaticTyping for Java {} //! # impl StaticTyping for Rust {} //! assert_impl!(!StaticTyping: Rust); //! ``` #[macro_export] macro_rules! assert_impl { ($trait:path: $($ty:ty),+) => {{ struct Helper<T>(T); trait AssertImpl { fn assert() {} } impl<T: $trait> AssertImpl for Helper<T> {} $( Helper::<$ty>::assert(); )+ }}; (!$trait:path: $($ty:ty),+) => {{ struct Helper<T>(T); trait AssertImpl { fn assert() {} } impl<T: $trait> AssertImpl for Helper<T> {} trait AssertNotImpl { fn assert() {} } $( impl AssertNotImpl for Helper<$ty> {} Helper::<$ty>::assert(); )+ }}; }