Custom Operators in Swift

Gurjit Singh

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May 4, 2020 · 2 min read

Swift provides a very useful feature which is to define your own custom operators. It is a very confusing topic in the beginning but it is very powerful to use. It increases our code readability and provides a very clear and concise way to write code.

You can declare custom operators by defining static type method inside an extension. First of all, you have to decide your operator type that is it prefix, infix or postfix.

Prefix Operators

You can declare prefix operator with prefix modifier before the func keyword.

extension String {
     static prefix func !! (name: String) -> String {
           return "Hello " + name
     }
}print(!!"Gurjit")
//will print Hello Gurjit

In the above example:

• First of all, implements extension String
• Then, defines prefix operator !! and this method started with the static keyword
• The static method takes one string argument called name
• Finally, return string after concatenating name argument with “Hello”

Infix Operators

Infix operators are different than prefix operators and postfix operators. In Infix operators we have to define its precedence and associativity.

We are not talking about precedence and associativity in this article but if you want an explanation for this topic please go-ahead to this link.

infix operator ^^: MultiplicationPrecedenceextension Int {
      static func ^^ (num: Int, power: Int) -> Int {
           return Int(pow(Double(num), Double(power)))
      }
}print(5 ^^ 2)

In the above example,

• First, defines a custom infix operator ^^ which belongs to MultiplicationPrecedence group
• Then, implements extension Int
• Defines static function ^^ which takes two parameters num and power and return the power of the number

Postfix Operators

You can declare postfix operator with postfix modifier before the func keyword.

extension Double {
       static postfix func % (percentage: Double) -> Double {
              return (Double(percentage) / 100)
       }
}print(30%)
//will print 0.3

In the above example:

• First of all, implements extension Double
• Then, defines postfix operator % and this method started with the static keyword
• The static method takes one string argument called percentage
• Finally, return double after calculating the percentage

Conclusion

As the examples show custom operators are very useful to reduce code duplication and provides a very clean way to write code.

It’s very handy to write custom operators to write robust code when working in teams, that code is understood by others.

Thanks!