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1 | /// A macro for defining `#[cfg]` if-else statements. | |
2 | /// | |
3 | /// This is similar to the `if/elif` C preprocessor macro by allowing definition | |
4 | /// of a cascade of `#[cfg]` cases, emitting the implementation which matches | |
5 | /// first. | |
6 | /// | |
7 | /// This allows you to conveniently provide a long list `#[cfg]`'d blocks of code | |
8 | /// without having to rewrite each clause multiple times. | |
9 | macro_rules! cfg_if { | |
10 | ($( | |
11 | if #[cfg($($meta:meta),*)] { $($it:item)* } | |
12 | ) else * else { | |
13 | $($it2:item)* | |
14 | }) => { | |
15 | __cfg_if_items! { | |
16 | () ; | |
17 | $( ( ($($meta),*) ($($it)*) ), )* | |
18 | ( () ($($it2)*) ), | |
19 | } | |
20 | } | |
21 | } | |
22 | ||
23 | macro_rules! __cfg_if_items { | |
24 | (($($not:meta,)*) ; ) => {}; | |
25 | (($($not:meta,)*) ; ( ($($m:meta),*) ($($it:item)*) ), $($rest:tt)*) => { | |
26 | __cfg_if_apply! { cfg(all(not(any($($not),*)), $($m,)*)), $($it)* } | |
27 | __cfg_if_items! { ($($not,)* $($m,)*) ; $($rest)* } | |
28 | } | |
29 | } | |
30 | ||
31 | macro_rules! __cfg_if_apply { | |
32 | ($m:meta, $($it:item)*) => { | |
33 | $(#[$m] $it)* | |
34 | } | |
35 | } |