So for example this code:

func trigramSimilarity(to other: Set<String>) -> Double {
    let selfTrigram = trigrams()
    let total = selfTrigram.union(other)
    let common = selfTrigram.intersection(other)
    return total.isEmpty ? 0 : Double(common.count) / Double(total.count)
}

I would hope the compiler transforms to

func trigramSimilarity(to other: Set<String>) -> Double {
    let selfTrigram = trigrams()
    let total = selfTrigram.union(other)
    return total.isEmpty ? 0 : Double(selfTrigram.intersection(other).count) / Double(total.count)
}

By noticing that let common is not needed if total.isEmpty the swift compiler could allow me to write simpler code but avoid unnecessary calculations.

But is it safer to just be explicit?