Generator function execution model in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a generator function that yields numbers from 1 to 3.

PHP

<?php
function numbers() {
    yield [1];
}

foreach (numbers() as $num) {
    echo $num . " ";
}
?>

Drag options to blanks, or click blank then click option'

A1

B5

C0

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Yielding 0 instead of 1.

Yielding the last number directly without starting from 1.

The generator yields the number 1 first. Using yield 1; starts the sequence.

2fill in blank

medium

Complete the code to yield numbers from 1 to 3 using a loop inside the generator.

PHP

<?php
function numbers() {
    for ($i = 1; $i <= [1]; $i++) {
        yield $i;
    }
}

foreach (numbers() as $num) {
    echo $num . " ";
}
?>

Drag options to blanks, or click blank then click option'

A5

B1

C3

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 5 instead of 3, which yields extra numbers.

Using 0 which yields no numbers.

The loop should run until 3 to yield numbers 1, 2, and 3.

3fill in blank

hard

Fix the error in the generator function to correctly yield values.

PHP

<?php
function gen() {
    [1] 1;
    [1] 2;
    [1] 3;
}

foreach (gen() as $val) {
    echo $val . " ";
}
?>

Drag options to blanks, or click blank then click option'

Ayield

Breturn

Cecho

Dprint

Attempts:

3 left

💡 Hint

Common Mistakes

Using return instead of yield.

Using echo or print inside the generator.

In a generator, yield is used to produce values one at a time.

4fill in blank

hard

Fill both blanks to create a generator that yields squares of numbers from 1 to 4.

PHP

<?php
function squares() {
    for ($i = 1; $i [1] 4; $i++) {
        yield $i [2] 2;
    }
}

foreach (squares() as $sq) {
    echo $sq . " ";
}
?>

Drag options to blanks, or click blank then click option'

A<=

B**

C*

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using * instead of ** which multiplies but does not square.

Using < which excludes 4.

The loop runs while $i is less than or equal to 4, and squares are calculated using the exponent operator **.

5fill in blank

hard

Fill all three blanks to create a generator that yields only even numbers from 2 to 6.

PHP

<?php
function evens() {
    for ($n = [1]; $n [2] 6; $n += 2) {
        yield [3];
    }
}

foreach (evens() as $even) {
    echo $even . " ";
}
?>

Drag options to blanks, or click blank then click option'

A1

B<=

C$n

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Starting from 1 which is odd.

Using < which excludes 6.

Yielding a fixed number instead of $n.

The loop starts at 2, runs while $n is less than or equal to 6, and yields $n each time.

Practice

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

easy

A. It pauses the function and returns a value to the caller.

B. It immediately ends the function and returns a value.

C. It creates a new variable inside the function.

D. It calls another function asynchronously.

Solution

1. Step 1: Understand the role of yield in generators

   The yield keyword pauses the function execution and sends a value back to the caller without ending the function.

2. Step 2: Compare with other options

   Unlike return, yield does not end the function but allows it to resume later.

3. Final Answer:

   It pauses the function and returns a value to the caller. -> Option A

4. Quick Check:

   yield pauses and returns value [OK]

Hint: Remember: yield pauses, return ends function [OK]

Common Mistakes:

• Confusing yield with return
• Thinking yield creates variables
• Assuming yield calls other functions

2. Which of the following is the correct syntax to define a generator function in PHP?

easy

A. function gen() { return yield 1; }

B. function gen() { yield 1; }

C. function gen() => yield 1;

D. generator gen() { yield 1; }

Solution

1. Step 1: Identify correct generator syntax

   In PHP, a generator function is a normal function that uses yield inside its body.

2. Step 2: Check each option

   function gen() { yield 1; } uses a normal function with yield correctly. function gen() { return yield 1; } misuses return yield. function gen() => yield 1; uses invalid arrow syntax. generator gen() { yield 1; } uses an invalid keyword generator.

3. Final Answer:

   function gen() { yield 1; } -> Option B

4. Quick Check:

   Normal function + yield = generator [OK]

Hint: Generator = function with yield inside braces [OK]

Common Mistakes:

• Using return with yield incorrectly
• Trying arrow function syntax for generators
• Using non-existent keywords like 'generator'

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

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

medium

A. 123

B. Error: Cannot use foreach on generator

C. 1,2,3

D. 1 2 3

Solution

1. Step 1: Understand generator yields

   The generator yields values 1, then 2, then 3 in sequence.

2. Step 2: Analyze foreach output

   The foreach loops over each yielded value and echoes it followed by a space, so output is "1 2 3 "

3. Final Answer:

   1 2 3 -> Option D

4. Quick Check:

   foreach prints each yield with space [OK]

Hint: foreach prints each yield value in order [OK]

Common Mistakes:

• Ignoring spaces in echo output
• Thinking foreach can't iterate generators
• Confusing output format with commas

4. Identify the error in this PHP generator function:

function gen() {
  yield 1;
  return 2;
  yield 3;
}
foreach (gen() as $v) {
  echo $v;
}

medium

A. Syntax error: return not allowed in generator

B. No error, outputs 123

C. The return ends generator early, so yield 3 is never reached

D. foreach cannot iterate generator with return

Solution

1. Step 1: Understand return in generators

   Return ends the generator function immediately, so code after return is not executed.

2. Step 2: Analyze code flow

   After yielding 1, the return 2 ends the generator, so yield 3 is never reached or yielded.

3. Final Answer:

   The return ends generator early, so yield 3 is never reached -> Option C

4. Quick Check:

   Return stops generator, later yields skipped [OK]

Hint: Return ends generator; yields after return ignored [OK]

Common Mistakes:

• Thinking return causes syntax error
• Expecting all yields to run despite return
• Assuming foreach can't handle return in generator

5. Given this generator function, what will be the output?

function gen() {
  for ($i = 0; $i < 3; $i++) {
    yield $i => $i * 2;
  }
}
foreach (gen() as $key => $value) {
  echo "$key:$value ";
}

hard

A. 0:0 1:2 2:4

B. 0:0 1:1 2:2

C. 0 2 4

D. Error: Cannot yield key => value in PHP

Solution

1. Step 1: Understand yield with key => value

   The generator yields keys 0,1,2 with values 0,2,4 respectively (value = key * 2).

2. Step 2: Analyze foreach output

   foreach prints each key and value separated by colon and space, so output is "0:0 1:2 2:4 "

3. Final Answer:

   0:0 1:2 2:4 -> Option A

4. Quick Check:

   Yield key=>value prints key:value pairs [OK]

Hint: Yield key=>value pairs print as key:value [OK]

Common Mistakes:

• Confusing value with key
• Thinking yield key=>value is invalid
• Ignoring spaces in output