macro_rules! ensure {
($cond:expr, $msg:literal $(,)?) => { ... };
($cond:expr, $err:expr $(,)?) => { ... };
($cond:expr, $fmt:expr, $($arg:tt)*) => { ... };
}
Expand description
Return early with an error if a condition is not satisfied.
This macro is equivalent to if !$cond { return Err(From::from($err)); }
.
Analogously to assert!
, ensure!
takes a condition and exits the function
if the condition fails. Unlike assert!
, ensure!
returns an Error
rather than panicking.
Example
ensure!(user == 0, "only user 0 is allowed");
#[derive(Error, Debug)]
enum ScienceError {
#[error("recursion limit exceeded")]
RecursionLimitExceeded,
...
}
ensure!(depth <= MAX_DEPTH, ScienceError::RecursionLimitExceeded);