Example in the readme fails to compile: `some(3).or(7)`

[AndrejMitrovic]

Hi,

I'm trying this out with DMD v2.102.0 with the Includes a generic or range algorithm example on https://github.com/aliak00/optional#features:

import optional;

void main() {
    auto a = some(3);
    auto b = a.or(7);
}

lib/optional/source/optional/or.d(152,13): Error: expected return type of `int`, not `Optional!int`:
lib/optional/source/optional/or.d(150,13):        Return type of `int` inferred here.
lib/optional/source/optional/or.d(189,17): Error: template instance `optional.or.or!(Optional!int, int).or.or!(elseValue, Optional!int)` error instantiating
test.d(5,18):        instantiated from here: `or!(Optional!int, int)`

This works however:

    auto a = some(3);
    auto b = a.or(some(7));

Maybe just some() was missing?

[SimonN]

Yes, or(some(7)) works and has the wanted meaning. This should be fixed in the readme.

There is a deeper usability concern here. I remember I fell for this, too, and it wasn't immediately clear for me either how to fix the usercode. It would be nice if the error told you explicitly to use or(some(7)), or if the library accepted or(7) outright.

I believe that the optional library wants to be really explicit with these things. There should be only non-misleading auto-conversion, and there should be no accidental hijacking of methods (= an optional!X should not call or override methods of X by accident). This is why there is oc for dispatching to methods.

[SimonN]

The readme should use a.frontOr(7).

The general rule is that or on an Optional!X chains with another Optional!X and frontOr chains with a bare X.