Type Alias RsCelFunction 

pub type RsCelFunction = dyn Fn(CelValue, Vec<CelValue>) -> CelValue;

Prototype for a function binding.

Rust-accelerated functions can be used to extend the base language’s functionality. The this argument refers to an object the function is being run on (i.e. foo.bar()). The args argument refers to any arguments passed to the function within the parenthesis, in order passed. The return value of a function should be a single ValueCell wrapped in a ValueCellResult.

An example of a function impl that collects the keys of an object and returns them as a list:

use rscel::*;

fn keys_impl(this: CelValue, args: &[CelValue]) -> CelResult<CelValue> {
    if args.len() == 0 {
        return Err(CelError::misc("keys() expects 0 arguments"));
    }

    if let CelValue::Map(map) = this {
        Ok(CelValue::from_list(map.keys().map(|x| x.as_str().into()).collect()))
    } else {
       Err(CelError::misc("keys() only supported for map type"))
    }
}