Swift version: 5.2
Operator overloading is the practice of adding new operators and modifying existing ones to do different things. Operators are those little symbols like +
, *
, and /
, and Swift uses them in a variety of ways depending on context – a string plus another string equals a combined string, for example, whereas an integer plus another integer equals a summed integer.
To create your own operator you need to tell Swift whether it should be prefix (before its operand; the values used with it), postfix (after its operand), or infix. The most common is infix: +
, -
, *
, and more are all infix.
To create a new operator, try adding this to a playground:
infix operator **
That’s the exponentiation operator, designed to raise one number to the power of another. Normally we’d use the pow()
function for that job, but with operator overloading we can make **
work instead.
Now you need to tell Swift what to do when it sees that operator. For example, when we write something like 2 ** 4
what does that mean?
What Swift wants is a function called **
, the name of our operator, where the left-hand side is one type and the right-hand side is another type. Which type is down to us, but **
is normally used with a Double
on either side, so we’re going to write a function that accepts two doubles and returns a double:
func **(lhs: Double, rhs: Double) -> Double {
return pow(lhs, rhs)
}
As you can see, the function itself is a cinch thanks to pow()
– we literally just pass on the numbers. Now this code should work in your playground:
let result = 2 ** 4
For more advanced uses, you also need to specify associativity and a precedence group, but what we have is fine to start with.
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This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.
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