Memory efficiency
Learn how generators save memory with large datasets.
Generators save memory
The call range(1, 1000000) builds an array of one million elements; all values are loaded into memory. A generator instead produces one value at a time and holds only one value in memory.
You can see this difference with memory_get_usage(). For large datasets, a generator uses far less memory than an array.
Lazy evaluation
A generator pauses at each yield. The value is produced only when requested by foreach or next(). This lets large datasets flow through without loading into memory.
A file can be read line by line, network data can be processed chunk by chunk. No intermediate arrays are built; one value enters memory at a time, is processed and released.
Exercise Write a squares generator
Write squares(int $n): \Generator: yield the square of each number from 1 to $n. Iterate squares(5) with foreach and print each square.
Show example solution
take int $n, return \Generator. Use a for loop to yield the square of each number from 1 to $n. Then iterate with foreach (squares(5) as $square) and echo $square . "\n";
Example solution:
<?php
function squares(int $n): \Generator {
for ($i = 1; $i <= $n; $i++) {
yield $i * $i;
}
}
foreach (squares(5) as $square) {
echo $square . "\n";
}Test yourself
-
What happens in the call range(1, 1000000)?
- Nothing, the function returns empty
- Only the first value is returned
- An array of one million elements is built in memory
- A generator is returned, values are produced lazily
Show answer
An array of one million elements is built in memory — Correct. range() loads all values into an array; it does not produce them lazily like a generator.
-
Measure memory usage
$before = ____(true); foreach (squares(5) as $s) { echo $s . "\n"; } $after = memory_get_usage(true);Show answer
$before = memory_get_usage(true); foreach (squares(5) as $s) { echo $s . "\n"; } $after = memory_get_usage(true); -
Match the memory concepts
- range()
- Piles all values into an array
- Generator
- Produces one value at a time
- yield
- Produces a value lazily
- memory_get_usage
- Measures memory usage