type ~std::iterator::Iterator<A>:Send does not implement any method in scope named map

[carl-eastlund]

Program:

fn imap<A,B>( i : ~Iterator<A>, f : &fn(A)->B ) { i.map(f) }
fn main () {}

Error:

iter.rs:1:50: 1:60 error: type `~std::iterator::Iterator<A>:Send` does not implement any method in scope named `map`
iter.rs:1 fn imap<A,B>( i : ~Iterator<A>, f : &fn(A)->B ) { i.map(f) }
                                                            ^~~~~~~~~~
error: aborting due to previous error

[bluss]

Iterator::map is not only a default method but it is called with self (by-value self), so it cannot be called here.

[carl-eastlund]

Is there a different way to write this function that will work? Or is it impossible to abstract over an iterator and still use map?

[thestinger]

You probably don't want to use trait objects, except in rare cases. You can use a generic function with an iterator:

fn foo<A: Iterator<int>>(xs: A) -> int {
    xs.map(|x| x * 2).fold(0, |a, b| a + b)
}

fn bar<A, B: Iterator<A>>(mut xs: B) -> bool {
    xs.len() != 0
}

[bluss]

(It should be possible to use .map with ~Iterator if the trait object is encapsulated in a wrapper struct that implements Iterator)