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01e83adc88
but a C-variadic method makes a trait dyn-incompatible. That is because methods from dyn traits, when cast to a function pointer, create a shim. That shim can't really forward the c-variadic arguments.
36 lines
954 B
Rust
36 lines
954 B
Rust
// Traits where a method is c-variadic are not dyn compatible.
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//
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// Creating a function pointer from a method on an `&dyn T` value creates a ReifyShim.
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// This shim cannot reliably forward C-variadic arguments. Thus the trait as a whole
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// is dyn-incompatible to prevent invalid shims from being created.
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#![feature(c_variadic)]
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#[repr(transparent)]
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struct Struct(u64);
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trait Trait {
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fn get(&self) -> u64;
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unsafe extern "C" fn dyn_method_ref(&self, mut ap: ...) -> u64 {
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self.get() + unsafe { ap.arg::<u64>() }
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}
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}
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impl Trait for Struct {
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fn get(&self) -> u64 {
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self.0
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}
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}
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fn main() {
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unsafe {
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let dyn_object: &dyn Trait = &Struct(64);
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//~^ ERROR the trait `Trait` is not dyn compatible
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assert_eq!(dyn_object.dyn_method_ref(100), 164);
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assert_eq!(
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(Trait::dyn_method_ref as unsafe extern "C" fn(_, ...) -> u64)(dyn_object, 100),
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164
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);
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}
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}
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