There is no way to create Box<str>

[japaric]

I'm working on #16918, and as part of the DSTification of Hash, I'm adding tests to make sure that hashing Box<[T]> and Box<str> work. But there doesn't seem to be a way to create a boxed str.

I tried the following:

fn main() {
    let _: Box<str> = box "a";
    //^~ error: mismatched types: expected `Box<str>`, found `Box<&'static str>`
    let _: Box<str> = box *"a";
    //^~ error: cannot move a value of type str: the size of str cannot be statically determined
}

cc @nick29581

[sfackler]

Vec had this added: http://doc.rust-lang.org/std/vec/struct.Vec.html#method.into_boxed_slice. We could do something similar for String.

[apasel422]

This is now possible via String::into_boxed_str.