50 lines
1.7 KiB
Rust
50 lines
1.7 KiB
Rust
/// Macro to cast an identifier or expression to another type with type checks.
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///
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/// Runs _code_ if _variable_ or _expression_ is of type _type_, otherwise run _fallback_.
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///
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/// # Syntax
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///
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/// * `reify!(`_variable_ or _expression_`,|`_temp-variable_`: `_type_`|` _code_`,` `||` _fallback_ `)`
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/// * `reify!(`_variable_ or _expression_`,|`_temp-variable_`: `_type_`|` _code_ `)`
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/// * `reify!(`_variable_ or _expression_ `=>` `Option<`_type_`>` `)`
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/// * `reify!(`_variable_ or _expression_ `=>` _type_ `)`
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#[macro_export]
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macro_rules! reify {
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($old:ident, |$new:ident : $t:ty| $code:expr, || $fallback:expr) => {{
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#[allow(clippy::redundant_else)]
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if std::any::TypeId::of::<$t>() == std::any::Any::type_id(&$old) {
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// SAFETY: This is safe because we already checked to make sure the two types
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// are actually the same.
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let $new: $t = unsafe { std::mem::transmute_copy(&std::mem::ManuallyDrop::new($old)) };
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$code
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} else {
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$fallback
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}
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}};
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($old:expr, |$new:ident : $t:ty| $code:expr, || $fallback:expr) => {{
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let old = $old;
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reify!(old, |$new: $t| $code, || $fallback)
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}};
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($old:ident, |$new:ident : $t:ty| $code:expr) => {
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reify!($old, |$new: $t| $code, || ())
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};
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($old:expr, |$new:ident : $t:ty| $code:expr) => {
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reify!($old, |$new: $t| $code, || ())
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};
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($old:ident => Option<$t:ty>) => {
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reify!($old, |v: $t| Some(v), || None)
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};
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($old:expr => Option<$t:ty>) => {
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reify!($old, |v: $t| Some(v), || None)
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};
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($old:ident => $t:ty) => {
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reify!($old, |v: $t| v, || unreachable!())
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};
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($old:expr => $t:ty) => {
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reify!($old, |v: $t| v, || unreachable!())
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};
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}
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