Yield from delegation in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of yield from delegation with nested generators

What is the output of the following PHP code?

PHP

<?php
function gen1() {
    yield 1;
    yield 2;
}

function gen2() {
    yield from gen1();
    yield 3;
}

foreach (gen2() as $value) {
    echo $value . ' ';
}
?>

A 3 1 2

B 1 3 2

C 2 1 3

D 1 2 3

💡 Hint

Remember that yield from passes all values from the delegated generator in order.

The function gen2 uses 'yield from gen1()', which yields 1 and 2 in order, then yields 3. So the output is '1 2 3 '.

❓ Predict Output

intermediate

Value returned by yield from delegation

What is the output of this PHP code?

PHP

<?php
function inner() {
    yield 1;
    yield 2;
    return 42;
}

function outer() {
    $result = yield from inner();
    yield $result;
}

foreach (outer() as $value) {
    echo $value . ' ';
}
?>

A 1 2

B 42 1 2

C 1 2 42

D 1 2 0

💡 Hint

The return value of the inner generator is captured by yield from and can be yielded afterwards.

The inner generator yields 1 and 2, then returns 42. The outer generator yields from inner(), capturing 42 in $result, then yields $result. So output is '1 2 42 '.

🔧 Debug

advanced

Identify the error in yield from usage

What error does this PHP code produce?

PHP

<?php
function gen() {
    yield from 123;
}

foreach (gen() as $v) {
    echo $v;
}
?>

A Syntax error: unexpected 'from'

B Fatal error: Cannot iterate over an integer

C Warning: Undefined variable

D No output, code runs silently

💡 Hint

yield from expects an iterable or generator, not a scalar value.

The code tries to yield from an integer 123, which is not iterable. This causes a fatal error about iterating over a non-iterable.

📝 Syntax

advanced

Correct yield from syntax in PHP

Which option shows the correct syntax to delegate yielding to another generator in PHP?

A yield from anotherGenerator();

B yield anotherGenerator();

C yieldfrom anotherGenerator();

D yield_from anotherGenerator();

💡 Hint

The keyword is two words separated by a space.

The correct syntax uses 'yield from' with a space. Other options are invalid syntax or yield the generator object itself.

🚀 Application

expert

Count total yielded values using yield from delegation

Given the following PHP code, what is the value of $count after execution?

PHP

<?php
function genA() {
    yield 1;
    yield 2;
}

function genB() {
    yield 3;
    yield 4;
}

function genC() {
    yield from genA();
    yield from genB();
    yield 5;
}

$count = 0;
foreach (genC() as $v) {
    $count++;
}
echo $count;
?>

A 5

B 4

C 6

D 3

💡 Hint

Count all values yielded by genA, genB, and the last yield in genC.

genA yields 2 values, genB yields 2 values, and genC yields one more value (5). Total is 2 + 2 + 1 = 5.