PHP 7 Return Type Declarations-Section-2

Introduction

In the previous tutorial, we looked at scalar type declarations. We focused on the data types of arguments that we were passing to functions. In this tutorial, we will look at how we can specify the data type of the result that a function returns.

Topics to be covered

We will cover the following topics

• Tutorial pre-requisites
• Type Declarations - Valid Types
• Return Type Declarations Techniques
  • None
  • Coercive
  • Strict
• PHP 7 Return Type Declaration Example

Tutorial Pre-requisites

For you to successfully complete this tutorial, you should have/know the following.

• This tutorial assumes that you know the basics of PHP.
• You have an IDE such as NetBeans or a text editor i.e. Sublime Text, Brackets etc.
• You have PHP 7 and a web server already installed and running.
• You have a modern web browser
• You read the previous tutorial that introduces PHP 7. This is optional but highly recommended.

Type Declarations - Valid Types

The following are the supported types

1. class / interface
2. self
3. array
4. callable
5. bool
6. float
7. int
8. string

Return Type Declarations Techniques

The rules for declaring return types are not different from the ones for declaring scalar types.

• None – no type is explicitly specified
• Coercive – coerces the result to the specified type
• Strict – the result must be of the specified data type. No exceptions

PHP 7 Return Type Declaration Example

In this section, we will create a simple project that demonstrates the usage of return types in PHP 7. We will look at two examples that use coercive and strict types.

Step 1 – Create a new project

I am using XAMPP on windows so I will just create a new directory php7-return-types in C:\htdocs\xampp

Step 2 – Create the following three files

1. coercive.php
2. strict.php

Step 3 – Code for coercive.php

Open coercive.php
Add the following code

<?php

function getSubTotal(int $quantity, int $price)  {
    return $quantity * $price;
}

$result = getSubTotal("3","2100");

echo "String parameter values returned : $result of data type " . gettype($result);

Load the following URL in your web browser

http://localhost/php7-return-types/coercive.php

You will get the following result

String parameter values returned : 6300 of data type integer

HERE,

• we passed in string parameters that were coerced into integers. Therefore, the result returned result is of integer data type.

Suppose we want to return the result as a string and not an integer. How do we do that?
Modify the above getSubTotal(…) function to the following

function getSubTotal(int $quantity, int $price) : string  {
    return $quantity * $price;
}

HERE,

• function getSubTotal(int $quantity, int $price) : string {…} the full colon followed by the desired scalar type is used to define the data type that the function should return. In our case, our function will return a string.

Save the changes
Load the following URL into your web browser

http://localhost/php7-return-types/coercive.php

You will get the following result

String parameter values returned : 6300 of data type string

HERE,

• The data type returned this time is a string. PHP converted the integer result into a string before the returning the result.

Step 4 – Code for strict.php

1. Open strict.php
2. Add the following code
   

   <?php
   
   declare(strict_types=1);
   
   function getSubTotal($quantity, $price) : int {
       return $quantity * $price;
   }
   
   echo "String parameter values returned : " . getSubTotal(3.1,2100.7);
   

HERE,
• declare(strict_types=1); activates strict typing. • function getSubTotal($quantity, $price) : int {…} sets int as the return type. Note we did not specify the data type for the $quantity and $price.
We deliberately passed in parameter values of float data type. The result will also be a float and PHP will throw an error because its expecting the result to be an integer and not float
Load the following URL into your web browser

http://localhost/php7-return-types/strict.php

You will get the following result

Fatal error: Uncaught TypeError: Return value of getSubTotal() must be of the type integer, float returned in C:\xampp\htdocs\php7-return-types\strict.php:6 Stack trace: #0 C:\xampp\htdocs\php7-return-types\strict.php(9): getSubTotal(3.1, 2100.7) #1 {main} thrown in C:\xampp\htdocs\php7-return-types\strict.php on line 6

HERE,

• Return value of getSubTotal() must be of the type integer, float returned in… tells us the expected return type should an integer and not float

Modify the code to pass integer values. You will get the output.

Summary

Return type declarations allow us to specify the expected data type that our function should return. The rules for return type declarations are very similar to the rules for scalar type declarations.

What’s Next?

The next tutorial will look at new operators in PHP 7 (Spaceship and Null Coalescing). In a nutshell, you can now have the option specify the variable data type when declaring variables.
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