Trait core::marker::Reflect
[−]
[src]
pub trait Reflect { }
Types that can be reflected over.
This trait is implemented for all types. Its purpose is to ensure that when you write a generic function that will employ reflection, that must be reflected (no pun intended) in the generic bounds of that function. Here is an example:
#![feature(reflect_marker)] fn main() { use std::marker::Reflect; use std::any::Any; #[allow(dead_code)] fn foo<T: Reflect + 'static>(x: &T) { let any: &Any = x; if any.is::<u32>() { println!("u32"); } } }#![feature(reflect_marker)] use std::marker::Reflect; use std::any::Any; fn foo<T: Reflect + 'static>(x: &T) { let any: &Any = x; if any.is::<u32>() { println!("u32"); } }
Without the declaration T: Reflect
, foo
would not type check
(note: as a matter of style, it would be preferable to write
T: Any
, because T: Any
implies T: Reflect
and T: 'static
, but
we use Reflect
here to show how it works). The Reflect
bound
thus serves to alert foo
's caller to the fact that foo
may
behave differently depending on whether T = u32
or not. In
particular, thanks to the Reflect
bound, callers know that a
function declared like fn bar<T>(...)
will always act in
precisely the same way no matter what type T
is supplied,
because there are no bounds declared on T
. (The ability for a
caller to reason about what a function may do based solely on what
generic bounds are declared is often called the "parametricity
property".)