Memory efficiency with generators in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of generator vs array memory usage

Consider the following PHP code that uses a generator and an array to produce numbers. What will be the output when running this code?

PHP

<?php
function genNumbers() {
    for ($i = 0; $i < 3; $i++) {
        yield $i;
    }
}

$generator = genNumbers();
$array = [0, 1, 2];

echo count($generator) . "," . count($array);
?>

A 0,3

B 3,3

C 1,3

D Fatal error: Uncaught Error: count(): Parameter must be an array or an object that implements Countable

💡 Hint

Remember that generators are not arrays and do not implement Countable interface.

In PHP, generators do not implement Countable, so calling count() on a generator causes a fatal error. Arrays can be counted normally.

🧠 Conceptual

intermediate

Why use generators for large data?

Why are generators more memory efficient than arrays when processing large datasets in PHP?

A Generators load all data into memory at once, making processing faster.

B Generators automatically compress data to save memory.

C Generators produce values one at a time, so they don't store the entire dataset in memory.

D Generators store data on disk instead of memory.

💡 Hint

Think about how generators yield values compared to arrays.

Generators yield one value at a time, so PHP does not need to keep the whole dataset in memory, unlike arrays which store all values at once.

🔧 Debug

advanced

Fix the memory leak in generator usage

This PHP code uses a generator to process a large file line by line. However, memory usage grows unexpectedly. What is the cause?

PHP

<?php
function readLines($file) {
    $handle = fopen($file, 'r');
    while (($line = fgets($handle)) !== false) {
        yield $line;
    }
    fclose($handle);
}

foreach (readLines('largefile.txt') as $line) {
    // process line
}
?>

A The generator does not close the file handle after iteration ends, causing a resource leak.

B The file handle is closed too early inside the generator.

C Using yield inside a while loop causes memory to accumulate.

D The fgets function reads the entire file into memory.

💡 Hint

Check when fclose is called relative to the generator's lifecycle.

The fclose($handle) is called after the while loop, but if the generator is not fully iterated, fclose may never run, leaving the file handle open and causing memory/resource leaks.

📝 Syntax

advanced

Identify the syntax error in generator function

Which option contains a syntax error in the generator function definition?

A function gen() { return yield 1; }

B function gen() { yield from [1, 2, 3]; }

C function gen() { yield 1; yield 2; }

D function gen() { yield; }

💡 Hint

Check if 'return yield' is valid syntax in PHP generators.

In PHP, 'return yield' is invalid syntax. You can either yield values or return a value, but not 'return yield'.

🚀 Application

expert

Calculate sum using generator for memory efficiency

You want to sum numbers from 1 to 1,000,000 without loading all numbers into memory at once. Which code correctly uses a generator to do this efficiently?

A

<?php
$numbers = range(1, 1000000);
$sum = array_sum($numbers);
echo $sum;
?>

B

<?php
function numbers() {
    for ($i = 1; $i <= 1000000; $i++) {
        yield $i;
    }
}
$sum = 0;
foreach (numbers() as $num) {
    $sum += $num;
}
echo $sum;
?>

C

<?php
function numbers() {
    return range(1, 1000000);
}
$sum = 0;
foreach (numbers() as $num) {
    $sum += $num;
}
echo $sum;
?>

D

<?php
function numbers() {
    for ($i = 1; $i <= 1000000; $i++) {
        return $i;
    }
}
$sum = 0;
foreach (numbers() as $num) {
    $sum += $num;
}
echo $sum;
?>

💡 Hint

Remember that 'yield' produces values one by one, while 'return' exits the function immediately.

Option B uses a generator with yield to produce numbers one at a time, saving memory. Option B loads all numbers into an array, using more memory. Option B returns an array, not a generator, so it loads all numbers. Option B returns immediately, so the foreach fails.