Union types in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a union type in PHP?

A union type allows a variable or parameter to accept values of multiple specified types. It is written using the pipe symbol (|) between types.

beginner

How do you declare a function parameter that accepts either an int or a string using union types?

You declare it like this: <code>function example(int|string $param) { }</code>. This means $param can be an int or a string.

intermediate

Can union types include null in PHP? How?

Yes. You can include null in a union type like int|null. This means the value can be an int or null.

intermediate

What happens if a value passed to a union typed parameter does not match any of the types?

PHP will throw a TypeError at runtime because the value does not match the declared union types.

advanced

Can you use union types with class types in PHP?

Yes. You can declare a parameter or property to accept multiple class types like <code>ClassA|ClassB</code>. The value must be an instance of either class.

Which symbol is used to declare union types in PHP?

A :

B &

C ,

D |

The pipe symbol (|) is used to separate types in a union type declaration.

What will happen if you pass a float to a parameter declared as int|string?

A It will accept the float without error.

B It will throw a TypeError.

C It will convert the float to int automatically.

D It will ignore the parameter.

Passing a float to a parameter declared as int|string causes a TypeError because float is not allowed.

Can union types include the type 'null'?

A Yes, by including null in the union.

B No, null cannot be part of union types.

C Only if the type is nullable with ?.

D Only for class types.

You can include null explicitly in union types, like int|null.

Which PHP version introduced union types?

A PHP 8.0

B PHP 7.4

C PHP 8.1

D PHP 7.2

Union types were introduced in PHP 8.0.

Is this a valid union type declaration? function test(int|float|string $value) {}

A No, float cannot be in union types.

B No, only two types allowed in union.

C Yes, it accepts int, float, or string.

D Yes, but only in PHP 7.

Union types can include multiple types separated by |, so this is valid.

Explain what union types are in PHP and how to use them in function parameters.

Think about allowing multiple types for one variable.

Describe what happens if a value does not match any type in a union type declaration.

Consider PHP's behavior when types don't match.

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