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

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of intersection type function call

What is the output of this PHP code using intersection types?

PHP

<?php
interface A { public function foo(): string; }
interface B { public function bar(): string; }
class C implements A, B {
    public function foo(): string { return 'foo'; }
    public function bar(): string { return 'bar'; }
}
function test( A&B $obj ): string {
    return $obj->foo() . '-' . $obj->bar();
}
$c = new C();
echo test($c);
?>

A SyntaxError

B foobar

C foo-barbar

D foo-bar

💡 Hint

Remember that the function requires an object implementing both interfaces A and B.

The function test accepts an object that implements both interfaces A and B. The class C implements both, so calling test($c) returns foo-bar.

❓ Predict Output

intermediate

Return type with intersection types

What will this PHP code output?

PHP

<?php
interface X { public function x(): string; }
interface Y { public function y(): string; }
class Z implements X, Y {
    public function x(): string { return 'X'; }
    public function y(): string { return 'Y'; }
}
function create(): X&Y {
    return new Z();
}
$obj = create();
echo $obj->x() . $obj->y();
?>

A XY

B X Y

C SyntaxError

D Fatal error: Return type mismatch

💡 Hint

The function returns an object implementing both interfaces X and Y.

The function create returns an instance of Z which implements both X and Y. So calling $obj->x() and $obj->y() outputs XY.

🔧 Debug

advanced

Identify the error with intersection types

What error will this PHP code produce?

PHP

<?php
interface M { public function m(): string; }
interface N { public function n(): string; }
class P implements M {
    public function m(): string { return 'm'; }
}
function callMN(M&N $obj): string {
    return $obj->m() . $obj->n();
}
$p = new P();
echo callMN($p);
?>

A Fatal error: Uncaught TypeError: Argument 1 passed to callMN() must implement interface N

B SyntaxError

C mnull

D Call to undefined method P::n()

💡 Hint

Check if the object passed implements both interfaces M and N.

The function callMN requires an object implementing both M and N. The class P only implements M. Passing $p causes a TypeError because P does not implement N.

📝 Syntax

advanced

Syntax error with intersection types

Which option shows the correct syntax to declare a function parameter with intersection types in PHP?

A function example(A && B $param): void {}

B function example(A & B $param): void {}

C function example(A&B $param): void {}

D function example(A | B $param): void {}

💡 Hint

Intersection types use a single ampersand without spaces.

The correct syntax for intersection types in PHP is A&B without spaces. Option C is correct. Option C has spaces which cause syntax error. Option C uses double ampersand which is invalid. Option C uses pipe which is union type, not intersection.

🚀 Application

expert

Using intersection types with traits and interfaces

Given the code below, what will be the output?

PHP

<?php
interface I1 { public function get(): string; }
interface I2 { public function get(): string; }
trait T1 { public function get(): string { return 'Trait'; } }
class MyClass implements I1, I2 {
    use T1;
}
function show(I1&I2 $obj): string {
    return $obj->get();
}
$instance = new MyClass();
echo show($instance);
?>

A Interface method get() must be public

B Trait

C SyntaxError

D Fatal error: Class MyClass must implement method get()

💡 Hint

Traits can provide method implementations for interfaces.

The class MyClass implements both interfaces I1 and I2 and uses trait T1 which provides the get() method. So calling show($instance) outputs Trait.