Generator function execution model in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple generator with yield

What is the output of this PHP code when executed?

PHP

<?php
function gen() {
    yield 1;
    yield 2;
    yield 3;
}
foreach (gen() as $value) {
    echo $value . ' ';
}
?>

A 1 2 3

B 123

C Array

D Error: Cannot use foreach on generator

💡 Hint

Remember that yield produces values one by one and foreach iterates over them.

The generator yields values 1, 2, and 3 sequentially. The foreach loop prints each value followed by a space, resulting in '1 2 3 '.

❓ Predict Output

intermediate

Generator state after partial iteration

What will be the output of this PHP code?

PHP

<?php
function gen() {
    yield 'a';
    yield 'b';
    yield 'c';
}
$g = gen();
echo $g->current();
$g->next();
echo $g->current();
?>

A Error: Cannot call current() before next()

B bc

C ab

D a

💡 Hint

The generator starts at the first yield value before calling next().

When the generator is created, current() returns the first yielded value 'a'. After calling next(), current() returns the second yielded value 'b'. So the output is 'ab'.

🔧 Debug

advanced

Identify the error in generator usage

What error does this PHP code produce when run?

PHP

<?php
function gen() {
    yield 1;
    yield 2;
}
$g = gen();
$g->next();
$g->next();
$g->next();
echo $g->current();
?>

A Fatal error: Call to undefined method

B NULL

C Notice: Undefined offset

D Error: Cannot advance generator beyond end

💡 Hint

What happens when you call next() past the last yield?

After the generator yields 1 and 2, the third next() call moves the generator past the end. current() then returns NULL because the generator is finished.

🧠 Conceptual

advanced

Behavior of yield in generator with return

What is the output of this PHP code?

PHP

<?php
function gen() {
    yield 10;
    return 20;
}
$g = gen();
foreach ($g as $value) {
    echo $value . ' ';
}
echo $g->getReturn();
?>

A Error: getReturn() not supported

B 10

C 20

D 10 20

💡 Hint

The return value of a generator can be retrieved after iteration.

The generator yields 10, which is printed with a space. After iteration, getReturn() returns the value 20 from the return statement, which is then printed.

❓ Predict Output

expert

Generator with keys and values

What is the output of this PHP code?

PHP

<?php
function gen() {
    yield 'x' => 100;
    yield 'y' => 200;
}
foreach (gen() as $key => $value) {
    echo "$key:$value ";
}
?>

A x:100 y:200

B 100:x 200:y

C 0:100 1:200

D Error: Invalid key syntax

💡 Hint

Yield can specify keys for the generated values.

The generator yields keys 'x' and 'y' with values 100 and 200 respectively. The foreach loop prints each key and value separated by a colon and space.