// run-pass // Test that when we write `x.foo()`, we do not have to know the // complete type of `x` in order to type-check the method call. In // this case, we know that `x: Vec<_1>`, but we don't know what type // `_1` is (because the call to `push` comes later). To pick between // the impls, we would have to know `_1`, since we have to know // whether `_1: MyCopy` or `_1 == Box<i32>`. However (and this is the // point of the test), we don't have to pick between the two impls -- // it is enough to know that `foo` comes from the `Foo` trait. We can // codegen the call as `Foo::foo(&x)` and let the specific impl get // chosen later. trait Foo { fn foo(&self) -> isize; } trait MyCopy { fn foo(&self) { } } impl MyCopy for i32 { } impl<T:MyCopy> Foo for Vec<T> { fn foo(&self) -> isize {1} } impl Foo for Vec<Box<i32>> { fn foo(&self) -> isize {2} } fn call_foo_copy() -> isize { let mut x = Vec::new(); let y = x.foo(); x.push(0_i32); y } fn call_foo_other() -> isize { let mut x: Vec<_> = Vec::new(); let y = x.foo(); let z: Box<i32> = Box::new(0); x.push(z); y } fn main() { assert_eq!(call_foo_copy(), 1); assert_eq!(call_foo_other(), 2); }