Swift Custom Operators

Swift Custom Operators

Custom operators are underrated topic among iOS developers. Some people think they’re bad , whereas others love to use them.

Code can be written in less lines, while keeping it clear what is happening. Custom operators are also known as advanced operators and allow you to combine two instances with a self-chosen infix, prefix and postfix.

Today, I’m going to show you the benefits of custom operators, how they are used in projects.

Types of Operator

There are three different types of operators as following:-

  1. Unary operators: operators that work on only one operand (e.g., = and  !)
  2. Binary operators: work on two operands, such as + , - , *, etc.
  3. Ternary operator: works on three operands, e.g., ?: (ternary operator)

Operator notation

Notation defines the position of the operator when used with the operands, there are of three types

  • Infix: when the operators are used in between operands. e.g c = a + b where + is the infix operator
  • Prefix: when the operators are used before an operand, e.g., ++, --, and !
  • Postfix: when the operators are used after an operand, e.g., ! and ? Used for force unwrapping and optional chaining in swift

Operator precedence and associativity in Swift

Operator precedence

When working with operators in Swift, you should also know the priority order in which the operator is executed. Operator precedence only matters for infix operators, as they work on multiple operands.

e.g var ans = 5 + 2 * 4 // 2 * 4 is done first which yields 8, then we do 5 + 8 = 13

In the example, * has more precedence compared to +, which is why 2 * 4 is executed before 5 + 2.


Associativity is of two types:

  1. left: this means that the expression to the left will be resolved first
  2. right: this means the expression to the right will be resolved first

Commonly user operators

1. Assignment operator

= this symbol is used to assign values to variable as well as constants

For example let a = 5

2. Arithmetic operators

Those type of operators used to perform a basic mathematical operations

e.g +, - , % , * , / and %

3. Logical operators

Those operators used to build a logical expressions

e.g., !, &&, and ||.

4.Comparison operators

Those operators are used to compare 2 values and return the bool depending on whether the comparison is true or not

e.g. >, <, ==, >=, <=, and !=.

5.Ternary operator

Since the Conditional Operator '?:' takes three operands to work, hence they are also called ternary operator. e.g ?:  —> 1 < 2 ? print(“1 is less then 2”) :  print(“1 is greater then 2”)

6. Nil coalescing operator

This operator is also known as ?? , and it gives the default value to optional arguments E.g. let num: Int? = nil

print(num ?? 0) 0 is the default value

Creating Custom Operators

Now let's create our own custom operators. in this section I will show you how we use operators in projects to make things easier.

Custom Infix Operator

Let’s create a new searching operator using '=?'. in the following example I will show you how to make searching more easier in projects.

Let's Start

Searchable protocol declaration

we have created a searchable protocol. its a protocol oriented approach which helps to create searching possible in any type.

Now we create a models in which we want to enable searching using custom protocols.

student and employee models declaration

so above we created two models named Student and Employee. as you notice, they inherit our Searchable protocol. so they need to return some unique name in searchableText as it is a getter.

Declared =? operator

So in the above code, we declared our infix '=?' operator, and defined its associativity to the left so that, if we use the operator chaining left, the problem will be solved first. and given the meaning or logic to operator.

Now Let's Use It

Data declaration

We created bunch of students and employees stored in array.

usage of operator and result

That's how we use custom infix operator

Custom Postfix Operator

Let’s create a custom object creating postfix operator with '++'

Employee protocol declaration

In above code we define a Employee blueprint or protocol with its name and constructor.

Model for employee inheriting its presentable protocol

now we defined a structure of Employee inheriting EmployeePresentable protocol and it's default case for empty object.

Defined a postfix operator

so we defined a postfix operator with its meaning within its function.

Usage of our postfix operator and result

As you can see in the above code creation of objects now easy with postfix operator

Custom Prefix Operator

Let’s create a custom object creating prefix operator with '++'

Prefix operator declaration with meaning

In the above example code, we define prefix operator with its meaning that every object that inherits EmployeePresentable protocol would increase its salary by 10.

Usage and result of prefix operator

Note:- Prefix Operator only take one object as parameter


This brings us to the conclusion of what operators are in Swift and how you can create your own. Although they are pretty simple to use, understanding them is important because they are one of the most foundational constructs of any programming language.

Define them only if the symbol’s original meaning makes sense for you.

Thanks for reading. Happy coding!