Yield keyword behavior in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP generator?

Consider the following PHP code using yield. What will it output when run?

PHP

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

A Error: yield used outside function

B 123

C 1 2 3

D Array

💡 Hint

Remember that yield produces values one by one, and the foreach loop prints each.

The generator function gen() 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

What does this PHP generator return?

What will be the output of this PHP code snippet?

PHP

<?php
function gen() {
    yield 'a' => 1;
    yield 'b' => 2;
}
foreach (gen() as $key => $value) {
    echo "$key:$value ";
}
?>

A a:1 b:2

B 1:a 2:b

C a b

D Error: Invalid key in yield

💡 Hint

Keys can be assigned in yield and are preserved in foreach.

The generator yields keys 'a' and 'b' with values 1 and 2 respectively. The foreach loop prints each key and value pair separated by a colon and space.

❓ Predict Output

advanced

What is the output of this nested generator?

Analyze the following PHP code with nested generators. What will it output?

PHP

<?php
function gen1() {
    yield 1;
    yield 2;
}
function gen2() {
    yield from gen1();
    yield 3;
}
foreach (gen2() as $v) {
    echo $v . ' ';
}
?>

A Error: yield from not supported

B 3 1 2

C 1 3 2

D 1 2 3

💡 Hint

The yield from keyword delegates yielding to another generator.

The gen2() function uses yield from gen1() to yield all values from gen1() first, then yields 3. The output is 1 2 3 .

❓ Predict Output

advanced

What error does this PHP code raise?

What error will this PHP code produce when executed?

PHP

<?php
function gen() {
    yield 1;
}
$gen = gen();
$gen->send(10);
?>

A No error, outputs 10

B Fatal error: Cannot send() to a generator that has not started

C 1

D 10

💡 Hint

You must start the generator before sending a value.

The send() method requires the generator to be started (at least one yield executed). Calling send() before starting causes a fatal error.

🧠 Conceptual

expert

How many values does this generator produce?

Given the following PHP generator code, how many values will be yielded when iterated?

PHP

<?php
function gen() {
    for ($i = 0; $i < 3; $i++) {
        if ($i === 1) {
            yield $i;
            continue;
        }
        yield $i * 2;
    }
}
$values = iterator_to_array(gen());
echo count($values);
?>

A 3

B 2

C 4

D 1

💡 Hint

Count how many times yield is called in the loop.

The loop runs 3 times (0,1,2). For i=0 and i=2, it yields i*2. For i=1, it yields i. So total yields: 3.