So I'm writing a compiler, and I wanted to create a list of TokenTypes (an enum) and check to see if the current token is among them. 'A-ha!', says I, 'I'll use std.algorithm!' (as I hadn't tried it really, yet, except for playing around) So I look it up, and find 'find'. It returns an iterated range, or an empty range on failure. A little funky, but that's okay, I can swing it!

immutable TokenType[] someList = [TokenType.Foo, TokenType.Bar];

...

while (find(someList, tokenStream.peek.type) != []) {
   doStuff();
}

If I have unittests on, this assert is triggered:

static assert(is(typeof(s) == Tuple!(string, float)));

I didn't at first, so I got another error. So I looked closer at the documentation, and it turns out it needs an input range, and that needs popFront! Well, it can't popFront an immutable range, so I dropped immutable, and decided to let convention and TLS sort the rest out!

This worked. Until I turned unittests on, and the assert I showed above tripped. At this point my language turned rather unpleasant and I wrote this:

bool contains(T)(const(T)[] l, T a)
{
     foreach(e; l) {
         if (a == e) {
            return true;
         }
     }
     return false;
}

And my problems went away. I assume what I experienced is a bug, but I'm not sure, so I thought I'd share my experience.

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