27 lines
973 B
Rust
27 lines
973 B
Rust
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/// Runs `$code` if `$old` is of type `$t`.
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#[macro_export]
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macro_rules! reify {
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($old:ident, |$new:ident : $t:ty| $code:expr, || $fallback:expr) => {{
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#[allow(unused_imports)]
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use ::std::{any::{Any, TypeId}, mem::{ManuallyDrop, transmute_copy}};
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if TypeId::of::<$t>() == $old.type_id() {
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// SAFETY: This is safe because we check to make sure the two types are
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// actually the same type.
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let $new: $t = unsafe { transmute_copy(&ManuallyDrop::new($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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}
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