Improve Regex equality

[pauldijou]

Right now, any Elm regex is considered equal to any other regex even if their definitions are totally different. Check demo.

Maybe improve Native.Utils.eq to perform a special check when testing regexps. Found this code browsing SO:

function regexSame(r1, r2) {
    if (r1 instanceof RegExp && r2 instanceof RegExp) {
        var props = ["global", "multiline", "ignoreCase", "source"];
        for (var i = 0; i < props.length; i++) {
            var prop = props[i];
            if (r1[prop] !== r2[prop]) {
                return false;
            }
        }
        return true;
    }
    return false;
}

[process-bot]

Thanks for the issue! Make sure it satisfies this checklist. My human colleagues will appreciate it!

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[process-bot]

Thanks for the issue! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.

[lukewestby]

@pauldijou can you share some reasons why you would want to check the equality of two regex values?

[lukewestby]

@pauldijou can you share some reasons why you would want to check the equality of two regex values?

[pauldijou]

I was messing around implementing a Map (like a Dict but with any type of key) and using Regex as keys broke it since all regexs were considered equals.

[pauldijou]

I was messing around implementing a Map (like a Dict but with any type of key) and using Regex as keys broke it since all regexs were considered equals.

[evancz]

Regex is similar to functions when it comes to equality. We will eventually be able to disallow using (==) on them statically, but it's not possible for now. So this will be "improved" by turning it into a compilation error once the compiler work happens.

[evancz]

Regex is similar to functions when it comes to equality. We will eventually be able to disallow using (==) on them statically, but it's not possible for now. So this will be "improved" by turning it into a compilation error once the compiler work happens.

[jvoigtlaender]

Maybe a note about Regex at http://package.elm-lang.org/packages/elm-lang/core/latest/Basics#== would be in place.

[jvoigtlaender]

Maybe a note about Regex at http://package.elm-lang.org/packages/elm-lang/core/latest/Basics#== would be in place.