Null Coalescing Operator "??" evaluates both of left and right side of expression, when right side throws Error.



This code:

    public errordomain SomeError {
        DUMMY_CODE
    }

    public class Something {
        private int value;
    
        public Something (int value = 0) {
            message ("Construction: %d", value);
        }
    
        public Something.throws_error (int value = 0) throws SomeError {
            this (value);
        }
    }

    public Something create_throwing (int value = 0) throws SomeError {
        return new Something (value);
    }

    public Something? create_nullable (int value = 0) {
        return new Something (value);
    }

    public void main () {
        try {
            Something? a = new Something (10);
            Something b = a ?? create_throwing (11);
        
            Something? c = new Something (101);
            Something? d = c ?? create_nullable (102);
        }
    
        catch (SomeError e) {
            assert_not_reached ();
        }
    }


Results in:

    ** Message: something.vala:9: Construction: 10
    ** Message: something.vala:9: Construction: 11
    ** Message: something.vala:9: Construction: 101

which means, create_throwing (11) is evaluated even a is not null.
create_nullable (102) isn't evaluated as  c  is not null.