1. Function pointer and closure

It is impossible to create a function pointer or closure from a function that can throw exceptions. Indeed, because funtion pointers type definition does not include the possibility to throw exception (and will not for verbosity, and annoyance reason), the Ymir language does not allow them to throw exception, in order to keep the guarantee of safety introduced by exception rethrowing. For that reason, the following example is not accepted by the compiler.

import std::io;


def main () {
    let x = |i : i32| => {
        assert (i < 10, "i must be lower than 10");
        println (i);
    };

     x (10);
}

Errors:

Error : a lambda function must be safe, but there are exceptions that are not caught
 --> main.yr:(5,13)
 5  ┃     let x = |i : i32| => {
    ╋             ^
    ┃ Note : &(core::exception::AssertError)
    ┃  --> main.yr:(6,9)
    ┃  6  ┃         assert (i < 10, "i must be lower than 10");
    ┃     ╋         ^
    ┗━━━━━┻━ 

Error : undefined symbol x
 --> main.yr:(10,6)
10  ┃      x (10);
    ╋      ^


ymir1: fatal error: 
compilation terminated.

To avoid that problem, every exception must be caught inside the lambda function.

1.1. Create function pointer from unsafe function

Sometimes it can be usefull to create function pointer from functions that are not safe (for example the function foo in the following example). To do that, the core modules, define a template function (cf. Templates, named toOption that transform a function symbol, into another function symbol that returns an option value. This other function symbol can be used to create a function pointer, using the ampersand (&) unary operator.

import std::io;

def foo (i : i32)-> void
    throws &AssertError
{
    assert (i < 10, "i must be lower than 10");
    println (i);
}


def main () {
    let x = & (toOption!foo);
    println (x (10));
    println (x (3));
}

Results:

Err(core::exception::AssertError (i must be lower than 10))
3
Ok()

Contribution This is not possible for method delegate.