47 lines
1.2 KiB
Rust
47 lines
1.2 KiB
Rust
//@ run-pass
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// Test that when we write `x.foo()`, we do not have to know the
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// complete type of `x` in order to type-check the method call. In
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// this case, we know that `x: Vec<_1>`, but we don't know what type
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// `_1` is (because the call to `push` comes later). To pick between
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// the impls, we would have to know `_1`, since we have to know
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// whether `_1: MyCopy` or `_1 == Box<i32>`. However (and this is the
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// point of the test), we don't have to pick between the two impls --
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// it is enough to know that `foo` comes from the `Foo` trait. We can
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// codegen the call as `Foo::foo(&x)` and let the specific impl get
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// chosen later.
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trait Foo {
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fn foo(&self) -> isize;
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}
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trait MyCopy { fn foo(&self) { } } //~ WARN method `foo` is never used
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impl MyCopy for i32 { }
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impl<T:MyCopy> Foo for Vec<T> {
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fn foo(&self) -> isize {1}
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}
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impl Foo for Vec<Box<i32>> {
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fn foo(&self) -> isize {2}
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}
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fn call_foo_copy() -> isize {
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let mut x = Vec::new();
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let y = x.foo();
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x.push(0_i32);
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y
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}
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fn call_foo_other() -> isize {
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let mut x: Vec<_> = Vec::new();
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let y = x.foo();
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let z: Box<i32> = Box::new(0);
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x.push(z);
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y
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}
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fn main() {
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assert_eq!(call_foo_copy(), 1);
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assert_eq!(call_foo_other(), 2);
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}
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