Function impls_send_weak 

pub fn impls_send_weak<T>() -> bool
where
    T: ?Sized,

Available on crate features alloc and unreliable only.

Returns true if the given type implements Send.

Use define_impls_trait_ignore_lt_fn macro to generate other trait implementation check functions.

Library tests ensure that the impls_trait checks are performed at compile time and fully optimized with no runtime cost at opt-level >= 1. Note that the release profile uses opt-level = 3 by default.

Reliability

While it is unlikely, there is still a possibility that this function may return false negatives in future Rust versions.

The correctness of the results returned by the functions depends on the following:

• Documented behavior that if T implements Eq, two Rcs that point to the same allocation are always equal: https://doc.rust-lang.org/1.82.0/std/rc/struct.Rc.html#method.eq.
• Undocumented behavior that the Rc::partial_eq implementation for T: Eq will not use PartialEq::eq if both Rcs point to the same memory location.
• The assumption that the undocumented short-circuit behavior described above will be retained for optimization purposes.

There is no formal guarantee that the undocumented behavior described above will be retained. If the implementation changes in a future Rust version, the function may return a false negative, that is, it may return false, even though T implements the trait. However, the implementation guarantees that a false positive result is impossible, i.e., the function will never return true if T does not implement the trait in any future Rust version.

Details:

• https://internals.rust-lang.org/t/rc-uses-visibly-behavior-changing-specialization-is-that-okay/16173/6,
• https://users.rust-lang.org/t/hack-to-specialize-w-write-for-vec-u8/100366,
• https://doc.rust-lang.org/1.82.0/std/rc/struct.Rc.html#method.eq,
• https://github.com/rust-lang/rust/issues/42655.