如何为任何可迭代类型实现特征？

Question

I'd like to implement a generic method that's callable on any container or iterator that iterates over a specific type, eg &[u32] , Vec<u32> , (0..99u32) , etc.

The following code does not compile:

trait Foo { fn foo(self); }

impl Foo for std::iter::IntoIterator<Item=u32> {
    fn foo(self) {}
}

error: the value of the associated type IntoIter (from the trait core::iter::IntoIterator ) must be specified [E0191]

 impl Foo for std::iter::IntoIterator<Item=u32> { 

What needs to be specified for the IntoIter associated type? ( std::iter::IntoIterator<Item=u32,IntoIter=???> )

so that this would work:

vec![0u32].foo()

Answer 1

The correct syntax here is impl<T> SomeTrait for T where T: OtherTrait . This works:

trait Foo { fn foo(self); }

impl<T> Foo for T 
    where T: std::iter::IntoIterator<Item=u32> 
{
    fn foo(self) {}
}

fn main() {
    vec![0u32].foo()
}