Swift extensions: Comparable limiters

Your code will likely contain some of these kind of statements:

    var b = calculateValue(a)

    if b > limit { b = limit }

Typically this kind of construction is used on array indicies as well.

    var b = calculateValue(a)

    if b > array.count { b = array.count }

My problem with this construction is that it is not immediately clear what is being done, I have to read it to see that in fact this is no more than limiting the calculated value to a certain maximum.

Luckily most of the numbers that we need this for implement the Comparable protocol. This allows us to write a little extension:

extension Comparable {

    

    func limitTo(max max: Self) -> Self {

        if self < max { return self }

        return max

    }

    func limitTo(min min: Self) -> Self {

        if self > min { return self }

        return min

    }

    

    func limitTo(min min: Self, max: Self) -> Self {

        return self.limitTo(max: max).limitTo(min: min)

    }

    mutating func limitInPlaceTo(min min: Self) {

        if self < min { self = min }

    }

    

    mutating func limitInPlaceTo(max max: Self) {

        if self > max { self = max }

    }

    

    mutating func limitInPlaceTo(min: Self, max: Self) {

        self = self.limitTo(min:min, max: max)

    }

}

With this extension the above lines can be rewritten as:

    var b = calculateValue(a).limitTo(max: limit)

and

    var b = calculateValue(a).limitTo(max: array.count)

Of course the other functions can be used as well:

    b.limitInPlaceTo(min: limit)

Another advantage is that using these functions can change some of the variable definitions from a var to a let because it is no longer necessary to perform the limiting operation separate.

Happy coding...

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