Union types in PHP - Mini Project: Build & Apply

Using Union Types in PHP

📖 Scenario: You are building a simple PHP program that handles user input which can be either a number or a text message. You want to accept both types safely using PHP's union types feature.

🎯 Goal: Create a function that accepts a parameter which can be either an int or a string. The function will return a message describing the type and value received.

📋 What You'll Learn

Create a function called describeInput that accepts a parameter with a union type int|string.

Inside the function, use is_int() to check if the input is an integer.

Return a string describing the input type and value.

Call the function with both an integer and a string and print the results.

💡 Why This Matters

🌍 Real World

Union types help PHP programs accept multiple types safely, which is common when handling user input or data from different sources.

💼 Career

Understanding union types is important for writing flexible and type-safe PHP code, a skill valued in modern PHP development jobs.

1

Create the describeInput function with a union type parameter

Write a function called describeInput that accepts one parameter named $input with the union type int|string. Inside the function, just return an empty string "" for now.

PHP

<?php

// Create the describeInput function with union type parameter
function describeInput(int|string $input): string {
    // Your code here
}

Hint

Use function describeInput(int|string $input): string to declare the function with a union type parameter.

2

Add type checking inside the function

Inside the describeInput function, use is_int($input) to check if $input is an integer. If it is, return the string "Input is an integer: " concatenated with the value of $input. Otherwise, return "Input is a string: " concatenated with $input.

PHP

<?php

// Create the describeInput function with union type parameter
function describeInput(int|string $input): string {
    // Your code here
}

Hint

Use if (is_int($input)) { ... } else { ... } to check the type and return the correct message.

3

Call the function with an integer and a string

Call the describeInput function twice: once with the integer 42 and once with the string "hello". Store the results in variables $result1 and $result2 respectively.

PHP

<?php

// Create the describeInput function with union type parameter
function describeInput(int|string $input): string {
    if (is_int($input)) {
        return "Input is an integer: " . $input;
    } else {
        return "Input is a string: " . $input;
    }
}

// Your code here

Hint

Call the function with 42 and "hello" and save the results in $result1 and $result2.

4

Print the results

Print the values of $result1 and $result2 each on a new line using echo.

PHP

<?php

// Create the describeInput function with union type parameter
function describeInput(int|string $input): string {
    if (is_int($input)) {
        return "Input is an integer: " . $input;
    } else {
        return "Input is a string: " . $input;
    }
}

$result1 = describeInput(42);
$result2 = describeInput("hello");

// Your code here

Hint

Use echo $result1 . "\n"; and echo $result2 . "\n"; to print each result on its own line.

Practice

1. What does a union type in PHP allow you to do?
function example(int|string $value) {}

easy

A. Only accept integer values

B. Accept multiple types for a parameter or return value

C. Only accept string values

D. Combine two functions into one

Solution

1. Step 1: Understand union type syntax

   The | symbol between types means the parameter can be either type.

2. Step 2: Analyze the example function

   The function accepts either an int or a string as input.

3. Final Answer:

   Accept multiple types for a parameter or return value -> Option B

4. Quick Check:

   Union types allow multiple types [OK]

Hint: Look for the | symbol to spot union types [OK]

Common Mistakes:

• Thinking union types combine functions
• Assuming only one type is allowed
• Confusing union types with type casting

2. Which of the following is the correct syntax for a union type in PHP 8+?
function test(?? $param) {}

easy

A. int|string, float $param

B. int&string $param

C. int|string&float $param

D. int|string $param

Solution

1. Step 1: Recall union type syntax

   Union types use the | symbol between types, e.g., int|string.

2. Step 2: Check each option

   int|string $param uses | correctly. int&string $param uses & which is intersection, not union. int|string&float $param mixes union and intersection incorrectly. int|string, float $param uses a comma which is invalid.

3. Final Answer:

   int|string $param -> Option D

4. Quick Check:

   Union types use | symbol [OK]

Hint: Union types always use | between types [OK]

Common Mistakes:

• Using & instead of | for union types
• Separating types with commas
• Mixing intersection and union syntax incorrectly

3. What will be the output of this PHP code?

function showType(int|string $value) {
    if (is_int($value)) {
        return "Integer: $value";
    } else {
        return "String: $value";
    }
}

echo showType(10) . "\n";
echo showType("hello") . "\n";

medium

A. 10\nhello

B. String: 10\nInteger: hello

C. Integer: 10\nString: hello

D. Error: Type mismatch

Solution

1. Step 1: Understand the function behavior

   The function checks if the input is an integer or string and returns a formatted string accordingly.

2. Step 2: Trace the calls

   Calling with 10 (int) returns "Integer: 10". Calling with "hello" (string) returns "String: hello".

3. Final Answer:

   Integer: 10\nString: hello -> Option C

4. Quick Check:

   Type check returns correct output [OK]

Hint: Check type with is_int or is_string inside function [OK]

Common Mistakes:

• Assuming output is just values without labels
• Confusing string and int outputs
• Expecting a type error for valid union types

4. Identify the error in this PHP function using union types:

function add(int|float $a, int|float $b): int|float {
    return $a + $b;
}

add(5, "10");

medium

A. Passing a string "10" instead of int or float causes a type error

B. Return type should be only int

C. Union types cannot be used in return types

D. Function should not accept two parameters

Solution

1. Step 1: Check parameter types

   The function expects parameters of type int or float only.

2. Step 2: Analyze the function call

   The call passes 5 (int) and "10" (string). String is not allowed, causing a type error.

3. Final Answer:

   Passing a string "10" instead of int or float causes a type error -> Option A

4. Quick Check:

   Parameter types must match union types exactly [OK]

Hint: Check argument types match union types exactly [OK]

Common Mistakes:

• Assuming string '10' is accepted as int
• Thinking union types disallow return types
• Ignoring parameter count

5. You want a function that accepts either an array of integers or a single integer and returns the sum. Which union type and code is correct?

function sumValues(?? $input): int {
    if (is_array($input)) {
        return array_sum($input);
    }
    return $input;
}

hard

A. int|array $input

B. int|string $input

C. array|float $input

D. int|bool $input

Solution

1. Step 1: Identify input types needed

   The function accepts either a single integer or an array of integers.

2. Step 2: Match union type to input

   int|array $input uses int|array, which matches the requirement. Others include wrong types like string, float, or bool.

3. Final Answer:

   int|array $input -> Option A

4. Quick Check:

   Union type matches all accepted input types [OK]

Hint: Match union types exactly to all input types needed [OK]

Common Mistakes:

• Using string or bool instead of array
• Not including all input types in union
• Confusing float with int