rust/src/test/run-pass/method-two-trait-defer-resolution-2.rs

// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

// Test that when we write `x.foo()`, we do nothave 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
// translate the call as `Foo::foo(&x)` and let the specific impl get
// chosen later.


#![allow(unknown_features)]
#![feature(box_syntax)]

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 0;
    x.push(z);
    y
}

fn main() {
    assert_eq!(call_foo_copy(), 1);
    assert_eq!(call_foo_other(), 2);
}