Convenience assert!-like macros which immediately return None or Err(...)
instead of panicking.
In a function returning an Option<T>, invoke the macro with just enough
parameters to get a condition to check.
rust
check!(a < n);
check_eq!(a, b);
This will expand to:
rust
if !(a < n) {
return None;
}
if a != b {
return None;
}
In a function returning a Result<T, E>, invoke the macro with an extra
argument, which is the error to return if the check fails (and must have type
E), just like you can add arguments to choose a panic message with assert!.
rust
check!(a < n, MyError::TooBig);
check_eq!(a, b, MyError::NotEqual);
This will expand to:
rust
if !(a < n) {
return Err(MyError::TooBig);
}
if a != b {
return Err(MyError::NotEqual);
}