51 lines
1.5 KiB
Rust
51 lines
1.5 KiB
Rust
//! Probe of the built in macro facilities.
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//!
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//! These tests record what `macro_rules!` can express for the workspace. They
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//! are kept as executable documentation of the decision to leave this crate
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//! empty for now: see the crate documentation.
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//!
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//! 内建宏设施探查。
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//!
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//! 这些测试记录 `macro_rules!` 能为工作区表达什么。它们被保留为「目前让本 crate
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//! 保持为空」这一决定的可执行文档：见 crate 文档。
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#[test]
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fn builtin_macros_can_substitute_a_type_and_a_literal() {
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// A `macro_rules!` macro can paste a type and a literal together, which
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// is the only form the workspace needs.
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// `macro_rules!` 宏可以把一个类型与一个字面量拼在一起，这是本工作区唯一需要的
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// 形式。
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macro_rules! quantity {
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($quantity:ty, $value:literal) => {
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<$quantity>::new($value)
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};
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}
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// `f64` has no `new`, so the probe uses a type that does.
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// `f64` 没有 `new`，故本探查用一个有的类型。
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struct Meters(f64);
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impl Meters {
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const fn new(value: f64) -> Self {
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Self(value)
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}
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}
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let value = quantity!(Meters, 1.5);
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assert_eq!(value.0, 1.5);
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}
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#[test]
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fn builtin_macros_can_dispatch_on_a_trailing_token() {
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macro_rules! to_meters {
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($value:literal m) => {
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$value
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};
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($value:literal km) => {
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$value * 1_000.0
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};
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}
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assert_eq!(to_meters!(2.5 m), 2.5);
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assert_eq!(to_meters!(2.5 km), 2_500.0);
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}
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