Memory efficiency with generators in PHP - Step-by-Step Execution

Concept Flow - Memory efficiency with generators

Start generator function

↓

Yield one value

↓

Pause function, keep state

↓

Request next value?

No→End generator

Yes↓

Resume function from pause

↓

Yield next value

↓

Repeat until done

The generator function yields one value at a time, pauses, and resumes on demand, saving memory by not storing all values at once.

Execution Sample

PHP

<?php
function countToThree() {
  yield 1;
  yield 2;
  yield 3;
}
foreach (countToThree() as $num) {
  echo $num . " ";
}

This code yields numbers 1 to 3 one by one, printing each without storing all at once.

Execution Table

Step	Generator State	Yielded Value	Action	Output
1	Start function	None	Yield 1	1
2	Paused after yield 1	1	Resume and yield 2	2
3	Paused after yield 2	2	Resume and yield 3	3
4	Paused after yield 3	3	Resume and end function
5	Function ended	None	Stop iteration

💡 Generator ends after yielding 3, no more values to yield.

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
Generator State	Not started	Paused after yield 1	Paused after yield 2	Paused after yield 3	Ended
Yielded Value	None	1	2	3	None

Key Moments - 3 Insights

Why doesn't the generator store all values at once?

Because it yields one value and pauses (see execution_table steps 1-3), it only keeps current state, saving memory.

What happens when the generator finishes yielding all values?

It ends the function and stops iteration (see execution_table step 5), so no more values are produced.

How does the foreach loop get each value from the generator?

Each loop iteration resumes the generator from pause, gets the next yielded value, then pauses again (see execution_table steps 2-4).

Visual Quiz - 3 Questions

Look at the execution table, what is the generator state after step 2?

A Paused after yield 2

B Function ended

C Paused after yield 1

D Not started

💡 Hint

Check the 'Generator State' column in execution_table row for step 2.

At which step does the generator stop yielding values?

A Step 3

B Step 5

C Step 4

D Step 2

💡 Hint

Look at the 'Action' column where it says 'Stop iteration' in execution_table.

If the generator yielded 5 values instead of 3, how would the variable 'Yielded Value' change in variable_tracker?

A It would have values up to 5 before final None

B It would stay the same with only 3 values

C It would end earlier

D It would never yield any value

💡 Hint

Check how 'Yielded Value' changes after each yield in variable_tracker.

Concept Snapshot

PHP generators yield values one at a time.
They pause after each yield, saving memory.
foreach resumes generator to get next value.
No full list stored in memory.
Useful for large data or streams.

Full Transcript

This example shows how PHP generators work to save memory. The function countToThree yields numbers 1, 2, and 3 one by one. Each yield pauses the function, keeping its state. The foreach loop resumes the generator to get the next value. This way, the program never stores all values at once, making it memory efficient. The execution table traces each step: starting the function, yielding values, pausing, resuming, and finally ending. The variable tracker shows how the generator state and yielded values change over time. Key moments clarify why generators save memory and how iteration stops. The quiz tests understanding of generator states and output. Overall, generators help handle data step-by-step without heavy memory use.