Intersection types in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

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

Consider the following PHP code that uses intersection types in a function parameter. What will be the output when calling process(new A_B())?

PHP

<?php
interface A { public function foo(): string; }
interface B { public function bar(): string; }
class A_B implements A, B {
    public function foo(): string { return "foo"; }
    public function bar(): string { return "bar"; }
}
function process(A&B $obj): string {
    return $obj->foo() . "-" . $obj->bar();
}
echo process(new A_B());

A foo-barbar

B foobar

C foo-bar

D Fatal error: Uncaught TypeError

💡 Hint

Remember that intersection types require the object to implement all interfaces listed.

The function process requires an object that implements both interfaces A and B. The class A_B implements both, so the method calls foo() and bar() return "foo" and "bar" respectively, joined by a dash.

❓ Predict Output

intermediate

What error does this PHP code raise with intersection types?

What error will this PHP code produce when calling process(new C())?

PHP

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

A Fatal error: Uncaught Error: Call to undefined method C::bar()

B foo-bar

C foo-

D Fatal error: Uncaught TypeError: Argument 1 passed to process() must implement interface B

💡 Hint

Check if the object implements all interfaces required by the intersection type.

The function process requires an object implementing both A and B. Class C only implements A, so passing it causes a TypeError before the function body runs.

🔧 Debug

advanced

Why does this PHP code with intersection types cause a fatal error?

This code intends to accept an object that implements both interfaces X and Y. Why does it cause a fatal error when calling handle(new Z())?

PHP

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

A Fatal error: Uncaught TypeError because Z does not implement interface Y

B Fatal error: Call to undefined method Z::y()

C Output: XY

D Output: X

💡 Hint

Intersection types require the object to implement all interfaces listed.

The function handle requires an object implementing both X and Y. Class Z only implements X, so passing it causes a TypeError before the function runs.

🚀 Application

advanced

Which class can be passed to this function with intersection types?

Given this function that requires an object implementing both Readable and Writable interfaces, which class can be passed without error?

PHP

<?php
interface Readable { public function read(): string; }
interface Writable { public function write(string $data): void; }
function operate(Readable&Writable $obj): string {
    $obj->write("data");
    return $obj->read();
}

A class File implements Readable { public function read(): string { return "file"; } }

B class File implements Readable, Writable { public function read(): string { return "file"; } public function write(string $data): void {} }

C class File implements Writable { public function write(string $data): void {} }

D class File {}

💡 Hint

The object must implement both interfaces to satisfy the intersection type.

Only class B implements both Readable and Writable, so it can be passed to operate without error.

🧠 Conceptual

expert

What is the main purpose of intersection types in PHP?

Choose the best description of what intersection types allow you to do in PHP.

A Require a value to satisfy multiple type constraints simultaneously, such as implementing multiple interfaces.

B Allow a value to be one of several types, like a union type.

C Define a new type that inherits properties from multiple classes.

D Automatically convert types during function calls.

💡 Hint

Think about how intersection types combine requirements.

Intersection types require a value to satisfy all listed types at once, for example, an object implementing multiple interfaces simultaneously.