Create a Rust Closure from a Rhai Function
Very useful as callback functions!
It is possible to further encapsulate a script in Rust such that it becomes a normal Rust closure.
Creating them is accomplished via the Func
trait which contains create_from_script
(as well as its companion method create_from_ast
).
use rhai::{Engine, Func}; // use 'Func' for 'create_from_script'
let engine = Engine::new(); // create a new 'Engine' just for this
let script = "fn calc(x, y) { x + y.len < 42 }";
// Func takes two type parameters:
// 1) a tuple made up of the types of the script function's parameters
// 2) the return type of the script function
//
// 'func' will have type Box<dyn Fn(i64, &str) -> Result<bool, Box<EvalAltResult>>> and is callable!
let func = Func::<(i64, &str), bool>::create_from_script(
// ^^^^^^^^^^^ function parameter types in tuple
engine, // the 'Engine' is consumed into the closure
script, // the script, notice number of parameters must match
"calc" // the entry-point function name
)?;
func(123, "hello")? == false; // call the closure
schedule_callback(func); // pass it as a callback to another function
// Although there is nothing you can't do by manually writing out the closure yourself...
let engine = Engine::new();
let ast = engine.compile(script)?;
schedule_callback(Box::new(move |x: i64, y: String| -> Result<bool, Box<EvalAltResult>> {
engine.call_fn(&mut Scope::new(), &ast, "calc", (x, y))
}));