Register a Fallible Rust Function
If a function is fallible (i.e. it returns a Result<_, Error>
), it can be registered with register_result_fn
(using the RegisterResultFn
trait).
The function must return Result<Dynamic, Box<EvalAltResult>>
.
#![allow(unused)] fn main() { use rhai::{Engine, EvalAltResult, Position}; use rhai::RegisterResultFn; // use 'RegisterResultFn' trait for 'register_result_fn' // Function that may fail - the result type must be 'Dynamic' fn safe_divide(x: i64, y: i64) -> Result<Dynamic, Box<EvalAltResult>> { if y == 0 { // Return an error if y is zero Err("Division by zero!".into()) // shortcut to create Box<EvalAltResult::ErrorRuntime> } else { Ok((x / y).into()) // convert result into 'Dynamic' } } let mut engine = Engine::new(); // Fallible functions that return Result values must use register_result_fn() engine.register_result_fn("divide", safe_divide); if let Err(error) = engine.eval::<i64>("divide(40, 0)") { println!("Error: {:?}", *error); // prints ErrorRuntime("Division by zero detected!", (1, 1)") } }
Create a Box<EvalAltResult>
Box<EvalAltResult>
implements From<&str>
and From<String>
etc.
and the error text gets converted into Box<EvalAltResult::ErrorRuntime>
.
The error values are Box
-ed in order to reduce memory footprint of the error path, which should be hit rarely.