Throw Exception on Error
All Engine
evaluation API methods return Result<T, Box<rhai::EvalAltResult>>
with EvalAltResult
holding error information.
To deliberately return an error, use the throw
keyword.
if some_bad_condition_has_happened {
throw error; // 'throw' any value as the exception
}
throw; // defaults to '()'
Exceptions thrown via throw
in the script can be captured in Rust by matching
EvalAltResult::ErrorRuntime(value, position)
with the exception value captured by value
.
let result = engine.eval::<i64>(
"
let x = 42;
if x > 0 {
throw x;
}
").expect_err();
println!("{}", result); // prints "Runtime error: 42 (line 5, position 15)"
Catch a Thrown Exception
It is possible to catch an exception instead of having it abort the evaluation
of the entire script via the try
… catch
statement common to many C-like languages.
fn code_that_throws() {
throw 42;
}
try
{
code_that_throws();
}
catch (err) // 'err' captures the thrown exception value
{
print(err); // prints 42
}