mirror of https://github.com/rust-lang/rust
56 lines
1.4 KiB
Rust
56 lines
1.4 KiB
Rust
#![feature(unsized_locals)]
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#![feature(unboxed_closures)]
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#![feature(tuple_trait)]
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pub trait FnOnce<Args: std::marker::Tuple> {
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type Output;
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extern "rust-call" fn call_once(self, args: Args) -> Self::Output;
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}
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struct A;
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impl FnOnce<()> for A {
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type Output = String;
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extern "rust-call" fn call_once(self, (): ()) -> Self::Output {
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format!("hello")
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}
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}
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struct B(i32);
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impl FnOnce<()> for B {
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type Output = String;
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extern "rust-call" fn call_once(self, (): ()) -> Self::Output {
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format!("{}", self.0)
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}
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}
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struct C(String);
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impl FnOnce<()> for C {
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type Output = String;
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extern "rust-call" fn call_once(self, (): ()) -> Self::Output {
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self.0
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}
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}
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struct D(Box<String>);
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impl FnOnce<()> for D {
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type Output = String;
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extern "rust-call" fn call_once(self, (): ()) -> Self::Output {
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*self.0
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}
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}
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fn main() {
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let x = *(Box::new(A) as Box<dyn FnOnce<(), Output = String>>);
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assert_eq!(x.call_once(()), format!("hello"));
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let x = *(Box::new(B(42)) as Box<dyn FnOnce<(), Output = String>>);
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assert_eq!(x.call_once(()), format!("42"));
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let x = *(Box::new(C(format!("jumping fox"))) as Box<dyn FnOnce<(), Output = String>>);
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assert_eq!(x.call_once(()), format!("jumping fox"));
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let x = *(Box::new(D(Box::new(format!("lazy dog")))) as Box<dyn FnOnce<(), Output = String>>);
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assert_eq!(x.call_once(()), format!("lazy dog"));
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}
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