Macro claim::assert_pending

macro_rules! assert_pending {
    ($cond:expr,) => { ... };
    ($cond:expr) => { ... };
    ($cond:expr, $($arg:tt)+) => { ... };
}

Asserts that expression returns Poll::Pending variant.

This macro is available for Rust 1.36+.

Uses

Assertions are always checked in both debug and release builds, and cannot be disabled. See debug_assert_pending! for assertions that are not enabled in release builds by default.

Custom messages

This macro has a second form, where a custom panic message can be provided with or without arguments for formatting. See std::fmt for syntax for this form.

Examples

let res: Poll<i32> = Poll::Pending;

assert_pending!(res);

// With custom messages
assert_pending!(res, "Future is not ready yet");

Poll::Pending variant will also be returned from this macro call:

let res: Poll<i32> = Poll::Pending;

let value = assert_pending!(res);
assert_eq!(value, Poll::Pending);

Poll::Ready(T) variant will cause panic:

let res = Poll::Ready(42);

assert_pending!(res);  // Will panic