Yield keyword behavior in PHP - Mini Project: Build & Apply

Yield keyword behavior

📖 Scenario: Imagine you have a list of tasks to do, but you want to handle them one by one without loading all at once. Using yield in PHP helps you do this efficiently.

🎯 Goal: You will create a generator function using yield to produce tasks one at a time, then loop through them to display each task.

📋 What You'll Learn

Create an array called $tasks with exact string values: 'Clean', 'Cook', 'Shop'

Create a generator function called taskGenerator that uses yield to return each task from $tasks

Use a foreach loop with variable $task to iterate over taskGenerator()

Print each task inside the loop using echo

💡 Why This Matters

🌍 Real World

Generators are useful when working with large data sets or streams where loading all data at once is not efficient.

💼 Career

Understanding <code>yield</code> helps in writing memory-efficient PHP code, useful in backend development and data processing jobs.

1

Create the tasks array

Create an array called $tasks with these exact string values: 'Clean', 'Cook', 'Shop'.

PHP

# Your code here

Hint

Use square brackets to create the array and separate values with commas.

2

Create the generator function

Create a generator function called taskGenerator that uses yield to return each task from the $tasks array.

PHP

<?php
$tasks = ['Clean', 'Cook', 'Shop'];

// Define the generator function taskGenerator
# Your code here

Hint

Use foreach to loop over $tasks and yield each $task.

3

Loop through the generator

Use a foreach loop with variable $task to iterate over taskGenerator().

PHP

<?php
$tasks = ['Clean', 'Cook', 'Shop'];

function taskGenerator() {
    global $tasks;
    foreach ($tasks as $task) {
        yield $task;
    }
}

// Loop through the generator
# Your code here

Hint

Use foreach with taskGenerator() and variable $task.

4

Print each task

Inside the foreach loop, print each $task using echo followed by a newline.

PHP

<?php
$tasks = ['Clean', 'Cook', 'Shop'];

function taskGenerator() {
    global $tasks;
    foreach ($tasks as $task) {
        yield $task;
    }
}

foreach (taskGenerator() as $task) {
    // Print each task
    # Your code here
}

Hint

Use echo $task . "\n"; to print each task on its own line.

Practice

1. What does the yield keyword do in a PHP function?

easy

A. It returns a value and pauses the function, resuming later to produce more values.

B. It immediately stops the function and returns a single value.

C. It creates a new variable inside the function.

D. It converts the function into a class method automatically.

Solution

1. Step 1: Understand yield behavior

   The yield keyword pauses the function and returns a value without ending it.

2. Step 2: Compare with return

   Unlike return, yield allows the function to resume and produce more values later.

3. Final Answer:

   It returns a value and pauses the function, resuming later to produce more values. -> Option A

4. Quick Check:

   Yield pauses and resumes function = A [OK]

Hint: Yield pauses function to produce values one by one [OK]

Common Mistakes:

• Confusing yield with return which ends function
• Thinking yield creates variables
• Assuming yield converts function to class method

2. Which of the following is the correct syntax to yield values from a function in PHP?

easy

A. yield($value);

B. return yield $value;

C. yield => $value;

D. yield $value;

Solution

1. Step 1: Recall yield syntax

   The correct syntax to yield a value is simply yield $value; inside the function.

2. Step 2: Check other options

   Options B, C, and D use invalid or incorrect syntax for yield in PHP.

3. Final Answer:

   yield $value; -> Option D

4. Quick Check:

   Simple yield syntax is 'yield $value;' [OK]

Hint: Yield uses simple 'yield $value;' syntax [OK]

Common Mistakes:

• Adding return before yield
• Using arrow (=>) with yield
• Calling yield like a function

3. What will be the output of this PHP code?

function gen() {
  yield 1;
  yield 2;
  yield 3;
}
foreach (gen() as $val) {
  echo $val . ' ';
}

medium

A. 1 2 3

B. Array

C. 123

D. Error: yield not allowed here

Solution

1. Step 1: Understand generator yields

   The function gen() yields values 1, 2, and 3 one by one.

2. Step 2: foreach prints each yielded value

   The foreach loop prints each value followed by a space, so output is '1 2 3 '.

3. Final Answer:

   1 2 3 -> Option A

4. Quick Check:

   Yielded values printed with spaces = B [OK]

Hint: Yield outputs values one by one in foreach loop [OK]

Common Mistakes:

• Expecting concatenated string without spaces
• Thinking yield returns an array
• Assuming syntax error with yield

4. Identify the error in this PHP code using yield:

function numbers() {
  yield 1
  yield 2;
}
foreach(numbers() as $n) {
  echo $n;
}

medium

A. foreach loop syntax is wrong

B. Missing semicolon after first yield statement

C. Cannot use yield inside a function

D. Yield must be followed by parentheses

Solution

1. Step 1: Check yield statements

   The first yield statement is missing a semicolon at the end, causing a syntax error.

2. Step 2: Validate other parts

   Using yield inside a function and foreach syntax are correct; yield does not require parentheses.

3. Final Answer:

   Missing semicolon after first yield statement -> Option B

4. Quick Check:

   Each yield needs semicolon [OK]

Hint: Check semicolons after yield statements [OK]

Common Mistakes:

• Forgetting semicolon after yield
• Thinking yield needs parentheses
• Assuming foreach syntax error

5. Given this PHP function using yield:

function filterPositive(array $numbers) {
  foreach ($numbers as $num) {
    if ($num > 0) {
      yield $num;
    }
  }
}

$values = [-2, 0, 3, 5, -1];
foreach (filterPositive($values) as $val) {
  echo $val . ',';
}

What is the output?

hard

A. 0,3,5,

B. -2,0,3,5,-1,

C. 3,5,

D. Error: yield cannot be used with if

Solution

1. Step 1: Analyze filtering condition

   The function yields only numbers greater than 0, so it skips -2, 0, and -1.

2. Step 2: Identify yielded values

   Only 3 and 5 satisfy the condition and are yielded, printed with commas.

3. Final Answer:

   3,5, -> Option C

4. Quick Check:

   Yield filters positive numbers only = D [OK]

Hint: Yield can filter values with if condition [OK]

Common Mistakes:

• Including zero or negative numbers
• Thinking yield can't be inside if
• Expecting all values printed