1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84

//! Macro for static assert that types implement a trait or not.
//!
//! # Example
//!
//! Assuming you have the following definitions:
//! ```
//! struct C;
//! struct Java;
//! struct JavaScript;
//! struct Python;
//! struct Rust;
//!
//! trait StaticTyped {}
//! impl StaticTyped for C {}
//! impl StaticTyped for Java {}
//! impl StaticTyped for Rust {}
//! ```
//!
//! This should build:
//! ```
//! # #[macro_use] extern crate assert_impl;
//! # struct C;
//! # struct Java;
//! # struct JavaScript;
//! # struct Python;
//! # struct Rust;
//! # trait StaticTyped {}
//! # impl StaticTyped for C {}
//! # impl StaticTyped for Java {}
//! # impl StaticTyped for Rust {}
//! assert_impl!(StaticTyped: C, Java, Rust);
//! assert_impl!(!StaticTyped: 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 StaticTyped {}
//! # impl StaticTyped for C {}
//! # impl StaticTyped for Java {}
//! # impl StaticTyped for Rust {}
//! assert_impl!(StaticTyped: JavaScript);
//! ```
//!
//! ```compile_fail
//! # #[macro_use] extern crate assert_impl;
//! # struct C;
//! # struct Java;
//! # struct JavaScript;
//! # struct Python;
//! # struct Rust;
//! # trait StaticTyped {}
//! # impl StaticTyped for C {}
//! # impl StaticTyped for Java {}
//! # impl StaticTyped for Rust {}
//! assert_impl!(!StaticTyped: 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();
         )+
    }};
}