Macro error_chain::ensure

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

Exits a function early with an error if the condition is not satisfied

The ensure! macro is a convenience helper that provides a way to exit a function with an error if the given condition fails.

As an example, ensure!(condition, "error code: {}", errcode) is equivalent to

if !condition {
    bail!("error code: {}", errcode);
}

See documentation for bail! macro for further details.