First-class callable syntax in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a first-class callable from the function strlen.

PHP

<?php
$func = [1](...);
echo $func('hello');
?>

Drag options to blanks, or click blank then click option'

Astrlen()

Bstrlen

C'strlen'

D&strlen

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around the function name creates a string, not suitable for first-class syntax.

Adding parentheses calls the function immediately instead of creating a callable.

In PHP 8.1+, to create a first-class callable from a function, use the function name without quotes or parentheses, followed by (...).

2fill in blank

medium

Complete the code to create a first-class callable from the function strtoupper using the callable syntax.

PHP

<?php
$func = [1](...);
echo $func('hello');
?>

Drag options to blanks, or click blank then click option'

Astrtoupper

B&strtoupper

Cstrtoupper()

D'strtoupper'

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes or parentheses instead of just the function name.

Trying to use the address-of operator (&) which is not valid here.

The first-class callable syntax for functions uses just the function name without quotes or parentheses, followed by (...).

3fill in blank

hard

Complete the code to create a first-class callable from the static method MyClass::myMethod.

PHP

<?php
class MyClass {
    public static function myMethod() {
        return 'Hello';
    }
}

$callable = [1](...);
echo $callable();
?>

Drag options to blanks, or click blank then click option'

AMyClass::myMethod

B'MyClass::myMethod'

C'MyClass::myMethod()'

DMyClass::myMethod()

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes creates an old-style string callable.

Adding parentheses calls the method immediately instead of creating a callable.

For static methods, the first-class callable syntax uses the class name, ::, and method name without quotes or parentheses, followed by (...).

4fill in blank

hard

Fill both blanks to create a first-class callable from an instance method myMethod of $obj.

PHP

<?php
class MyClass {
    public function myMethod() {
        return 'Hi';
    }
}
$obj = new MyClass();
$callable = [1]->[2](...);
echo $callable();
?>

Drag options to blanks, or click blank then click option'

A$obj

B'myMethod'

CmyMethod

D'MyClass::myMethod'

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around the method name (use bare identifier).

Using the class name instead of the object variable.

To create a first-class callable for an instance method, use $object->method(...) with the bare method name (no quotes).

5fill in blank

hard

Fill all three blanks to create a first-class callable from a closure stored in $closure and call it with argument 'world'.

PHP

<?php
$closure = fn($name) => "Hello, $name!";
$callable = [1];
echo $callable([2]);

// Using first-class callable syntax
$callable2 = [3];
echo $callable2('world');
?>

Drag options to blanks, or click blank then click option'

A$closure

B'world'

C$closure(...)

Dclosure

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to quote the closure variable name.

Not using quotes for the string argument.

Forgetting the spread operator (...) for first-class syntax.

Assign the closure variable directly as it's already callable. Call it with the string argument. Use $closure(...) for explicit first-class callable syntax.