go is supposed to be "simple", but I just spent half an hour implementing sets because the standard library has no way to test if a slice contains an element, so it;s impossible to say if its productive or not,
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Before the dawn of data structure galore in JS, we'd do `set = slice.reduce((acc, key) => (acc[key] = true, acc), {})` and later call `set.hasOwnProperty(whatYoureLookingFor)`. And let me tell you, we felt really clever! (Also, a loop would've been faster.)
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