# Trait core::marker::Reflect [−] [src]

    pub trait Reflect { }

Unstable (`reflect_marker` #27749)

: requires RFC and more experience

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".)

## Implementors

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