PHP
Pipeline with generators
Learn to chain multiple generators as a pipeline for data flow.
Generator pipelines
You can chain several generators: each generator takes the previous one's output and processes it. Data flows through; no intermediate arrays are built.
For example, one generator produces numbers, a second filters, a third transforms. Each step carries a single value, so large datasets are processed without loading into memory.
return and getReturn()
A generator can return a final value with return. This value is not yielded; after the generator has finished, you read it with getReturn().
This is useful to summarize the result of a stream. For example, you can yield numbers and at the end of the loop return $sum / $count; the average.
Exercise Filter and transform pipeline
Write filterEven(array $nums): \Generator: yield the even numbers. Write squares(array $nums): \Generator: iterate filterEven($nums) with foreach and yield the square of each value. Iterate squares([1, 2, 3, 4, 5, 6]) with foreach and print each square.
Show example solution
In filterEven, loop foreach ($nums as $n), if ($n % 2 === 0) yield $n;. In squares, loop foreach (filterEven($nums) as $n), yield $n * $n;. Then iterate foreach (squares([1, 2, 3, 4, 5, 6]) as $n) and echo $n . "\n";
Example solution:
<?php
function filterEven(array $nums): \Generator {
foreach ($nums as $n) {
if ($n % 2 === 0) {
yield $n;
}
}
}
function squares(array $nums): \Generator {
foreach (filterEven($nums) as $n) {
yield $n * $n;
}
}
foreach (squares([1, 2, 3, 4, 5, 6]) as $n) {
echo $n . "\n";
}
Exercise Compute the average and read it with getReturn
Write average(array $nums): \Generator: yield each number, then return the average. Create $gen = average([10, 20, 30]), iterate with foreach to print each number. Then print the average with $gen->getReturn().
Show example solution
" . $gen->getReturn() . "\n";
Example solution:
<?php
function average(array $nums): \Generator {
$sum = 0;
$count = 0;
foreach ($nums as $n) {
$sum += $n;
$count++;
yield $n;
}
return $sum / $count;
}
$gen = average([10, 20, 30]);
foreach ($gen as $n) {
echo $n . "\n";
}
echo "Average: " . $gen->getReturn() . "\n";
Test yourself
-
What is the advantage of a generator pipeline?
- Creates no intermediate arrays, saves memory
- Runs faster because it is parallel
- Loads all data into memory at once
- Automates error handling
Show answer
Creates no intermediate arrays, saves memory — Correct. Each step carries a single value; no intermediate arrays are built, memory is preserved.
-
Get the generator's final value
$gen = counter();
foreach ($gen as $n) { echo $n; }
echo $gen->____();
Show answer
$gen = counter();
foreach ($gen as $n) { echo $n; }
echo $gen->getReturn();
Next lesson: Summary - Generators
