type_val 0.3.2

Type-level values.
Documentation 
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

#![no_std]

//! This crate allows for the creation
//! of type-level values. Any value can
//! be type-level as long as it can be
//! initialized as a constant. All
//! type-level values implement the
//! TypeVal trait, and so can be provided
//! as type parameters.

/// A trait implemented by type-level
/// values.
pub trait TypeVal<T> {
    /// The value held.
    const VAL: T;
}

/// This macro is used to implement the
/// TypeVal trait. Any number of values
/// can be initialized with a single
/// invocation. Items prefixed by `pub`
/// are public. Attributes to be applied
/// to items in a block, including doc
/// comments, should go above their
/// targets.
///
/// ## Example
/// 
/// ```rust
/// def_type_val! {
///     type One: i32 = 1;
///     #[derive(Clone, Copy)]
///     type True: bool = true;
///     /// Negative one
///     pub type NegOne: i32 = -1;
///     pub type False: bool = false;
/// }
///
/// println!("One = {}, True = {}, NegOne = {}, False = {}",
///     One::VAL,
///     True::VAL,
///     NegOne::VAL,
///     False::VAL);
/// ```
#[macro_export]
macro_rules! def_type_val {
    {$(#[$attr:meta])* type $name:ident: $type:ty = $value:expr; $($next:tt)*} => {
        $(#[$attr])*
        struct $name;
        
        impl $crate::TypeVal<$type> for $name {
            const VAL: $type = $value;
        }
        
        def_type_val!($($next)*);
    };
    {$(#[$attr:meta])* pub type $name:ident: $type:ty = $value:expr; $($next:tt)*} => {
        $(#[$attr])*
        pub struct $name;
        
        impl $crate::TypeVal<$type> for $name {
            const VAL: $type = $value;
        }
        
        def_type_val!($($next)*);
    };
    () => {};
}