Union types in practice in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of function with union type return

What is the output of this PHP code using union types in the return declaration?

PHP

<?php
function test(int|string $input): int|string {
    if (is_int($input)) {
        return $input * 2;
    }
    return strtoupper($input);
}

echo test(5) . ' ' . test('hello');

A TypeError

B 5 hello

C 10 hello

D 10 HELLO

💡 Hint

Remember the function returns int or string depending on input type.

The function doubles the integer input and converts string input to uppercase. So test(5) returns 10 and test('hello') returns 'HELLO'.

❓ Predict Output

intermediate

Variable type with union type hint

What will be the output of this PHP code that uses union types for a variable?

PHP

<?php
/** @var int|string $var */
$var = 10;
if (is_string($var)) {
    echo 'string';
} elseif (is_int($var)) {
    echo 'int';
} else {
    echo 'other';
}

A int

B string

C other

D TypeError

💡 Hint

Check the actual value type assigned to the variable.

The variable $var is assigned the integer 10, so is_int($var) is true and 'int' is printed.

🔧 Debug

advanced

Identify the error with union types in method parameter

What error will this PHP code produce when calling the method with a float argument?

PHP

<?php
class Calculator {
    public function multiply(int|float $a, int|float $b): float {
        return $a * $b;
    }
}

$calc = new Calculator();
echo $calc->multiply(3.5, 2.0);

A TypeError: Argument 1 passed must be int|float, float given

B No error, outputs 7

C Fatal error: Return type must be float, int given

D Parse error: Syntax error in union type declaration

💡 Hint

Check if float is allowed in parameter and return types.

The method accepts int or float for parameters and returns a float. Multiplying 3.5 and 2.0 returns 7.0 with no error.

📝 Syntax

advanced

Which union type declaration is invalid?

Which of the following union type declarations in PHP is invalid and causes a syntax error?

A function foo(int|string $param): int|string {}

B function bar(int|float|null $param): int|float|null {}

C function baz(int|void $param): int|void {}

D function qux(string|false $param): string|false {}

💡 Hint

Check if 'void' can be used in union types.

'void' cannot be used as a union type with other types. It is only valid alone as a return type.

🚀 Application

expert

Determine the output of complex union type usage

What is the output of this PHP code that uses union types with nullable and mixed types?

PHP

<?php
function process(int|string|null $value): string|int|null {
    return match(true) {
        is_int($value) => $value * 3,
        is_string($value) => strtoupper($value),
        default => null
    };
}

var_dump(process(4));
var_dump(process('abc'));
var_dump(process(null));

A

int(12)
string(3) "ABC"
NULL

B

int(12)
string(3) "abc"
NULL

C TypeError on null input

D

int(4)
string(3) "ABC"
NULL

💡 Hint

Check how match expression handles each type and the return values.

For int input 4, it returns 4*3=12. For string 'abc', it returns 'ABC'. For null, it returns null. var_dump shows types and values.