Yield from delegation in PHP - Mini Project: Build & Apply

Yield from delegation

📖 Scenario: Imagine you are organizing a music playlist. You have different smaller playlists for genres like rock and jazz. You want to create one big playlist that plays all songs from these smaller playlists in order.

🎯 Goal: Build a PHP generator that uses yield from to combine multiple smaller playlists into one big playlist.

📋 What You'll Learn

Create two generators for small playlists with exact song names

Create a main generator that uses yield from to delegate to the smaller playlists

Iterate over the main generator to print all songs in order

💡 Why This Matters

🌍 Real World

Combining multiple data sources or streams into one sequence is common in music apps, data processing, and event handling.

💼 Career

Understanding generators and delegation helps write efficient code for handling large data or asynchronous tasks in PHP development.

1

Create the first playlist generator

Write a generator function called rockPlaylist that yields these exact songs in order: 'Bohemian Rhapsody', 'Stairway to Heaven', 'Hotel California'.

PHP

# Your code here

Hint

Use yield inside the function to return each song one by one.

2

Create the second playlist generator

Write a generator function called jazzPlaylist that yields these exact songs in order: 'So What', 'Take Five', 'Blue in Green'.

PHP

<?php
function rockPlaylist() {
    yield 'Bohemian Rhapsody';
    yield 'Stairway to Heaven';
    yield 'Hotel California';
}

# Your code here

Hint

Similar to the first playlist, use yield for each jazz song.

3

Create the main playlist generator using yield from

Write a generator function called mainPlaylist that uses yield from to delegate to rockPlaylist() first, then to jazzPlaylist().

PHP

<?php
function rockPlaylist() {
    yield 'Bohemian Rhapsody';
    yield 'Stairway to Heaven';
    yield 'Hotel California';
}

function jazzPlaylist() {
    yield 'So What';
    yield 'Take Five';
    yield 'Blue in Green';
}

# Your code here

Hint

Use yield from to include all songs from each smaller playlist.

4

Print all songs from the main playlist

Use a foreach loop to iterate over mainPlaylist() and print each song on its own line using echo.

PHP

<?php
function rockPlaylist() {
    yield 'Bohemian Rhapsody';
    yield 'Stairway to Heaven';
    yield 'Hotel California';
}

function jazzPlaylist() {
    yield 'So What';
    yield 'Take Five';
    yield 'Blue in Green';
}

function mainPlaylist() {
    yield from rockPlaylist();
    yield from jazzPlaylist();
}

# Your code here

Hint

Use foreach (mainPlaylist() as $song) and echo $song . "\n"; to print each song.

Practice

1.

What does the yield from statement do in PHP generators?

easy

A. It delegates yielding values from another generator or iterable.

B. It stops the generator immediately.

C. It converts a generator into an array.

D. It throws an exception inside the generator.

Solution

1. Step 1: Understand the purpose of yield from

   yield from is used to delegate yielding values from another generator or iterable, so you don't have to write a loop to yield each value manually.

2. Step 2: Compare with other options

   Stopping a generator, converting it to an array, or throwing exceptions are unrelated to yield from.

3. Final Answer:

   It delegates yielding values from another generator or iterable. -> Option A

4. Quick Check:

   yield from delegates values [OK]

Hint: Remember: yield from passes values from another generator [OK]

Common Mistakes:

• Thinking yield from stops the generator
• Confusing yield from with array conversion
• Assuming it throws exceptions

2.

Which of the following is the correct syntax to delegate yielding from another generator $gen inside a generator function?

function gen() {
    // your code here
}

easy

A. yield $gen;

B. yield to $gen;

C. yield($gen);

D. yield from $gen;

Solution

1. Step 1: Recall correct yield from syntax

   The correct syntax to delegate yielding from another generator is yield from $gen;.

2. Step 2: Check other options for syntax errors

   yield $gen; yields the generator object itself, not its values. yield($gen); is invalid syntax. yield to $gen; is not valid PHP syntax.

3. Final Answer:

   yield from $gen; -> Option D

4. Quick Check:

   Correct syntax uses yield from [OK]

Hint: Use exact phrase yield from to delegate generators [OK]

Common Mistakes:

• Using just yield $gen; instead of yield from
• Adding parentheses incorrectly
• Writing invalid keywords like 'yield to'

3.

What will be the output of the following PHP code?

function gen1() {
    yield 1;
    yield 2;
}

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

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

medium

A. 1 3 2

B. 3 1 2

C. 1 2 3

D. 1 2

Solution

1. Step 1: Understand yield from gen1() in gen2()

   This delegates yielding values 1 and 2 from gen1() inside gen2().

2. Step 2: Trace the output of the foreach loop

   The loop yields 1, then 2 from gen1(), then yields 3 from gen2(). So output is "1 2 3 "

3. Final Answer:

   1 2 3 -> Option C

4. Quick Check:

   Delegation yields 1,2 then 3 [OK]

Hint: Remember yield from outputs all delegated values first [OK]

Common Mistakes:

• Assuming order is changed
• Forgetting the last yield after delegation
• Thinking yield from yields the generator object

4.

Identify the error in this PHP generator code:

function genA() {
    yield 1;
    yield 2;
}

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

foreach (genB() as $val) {
    echo $val . ' ';
}

medium

A. It yields the generator object instead of its values.

B. Missing semicolon after yield statements.

C. Cannot yield inside a function.

D. The foreach loop is invalid syntax.

Solution

1. Step 1: Analyze yield genA(); in genB()

   This yields the generator object genA() itself, not the values it produces.

2. Step 2: Understand correct delegation with yield from

   To yield values from genA(), use yield from genA(); instead of yield genA();.

3. Final Answer:

   It yields the generator object instead of its values. -> Option A

4. Quick Check:

   Use yield from to delegate values [OK]

Hint: Use yield from to yield values, not the generator object [OK]

Common Mistakes:

• Using yield instead of yield from for delegation
• Assuming yielding a generator yields its values
• Ignoring the need to delegate properly

5.

Given two generators genX() yielding numbers 1 to 3 and genY() yielding numbers 4 to 6, how can you create a generator genZ() that yields all numbers from 1 to 6 using yield from?

function genX() {
    yield 1;
    yield 2;
    yield 3;
}

function genY() {
    yield 4;
    yield 5;
    yield 6;
}

function genZ() {
    // Fill in code here
}

hard

A. yield genX(); yield genY();

B. yield from genX(); yield from genY();

C. yield genX() + genY();

D. yield from genY(); yield from genX();

Solution

1. Step 1: Use yield from to delegate both generators in order

   To yield all numbers from 1 to 6 in sequence, delegate genX() first, then genY() using yield from.

2. Step 2: Check order and syntax

   yield from genX(); yield from genY(); yields 1,2,3 then 4,5,6. yield from genY(); yield from genX(); reverses order. Options B and C yield generator objects or invalid expressions.

3. Final Answer:

   yield from genX(); yield from genY(); -> Option B

4. Quick Check:

   Delegate generators in order with yield from [OK]

Hint: Chain generators with multiple yield from statements [OK]

Common Mistakes:

• Yielding generators instead of delegating
• Reversing the order of delegation
• Trying to add generators directly