The Generator class

PHP course · Expert · Lesson 2/54

Learn the Generator class's current(), next() and send() methods.

The Generator class methods

When a function containing yield is called, a Generator object is returned. Generator implements the Iterator interface; current() gives the current value, next() moves forward, valid() checks whether more values remain.

key() returns the yield's key; rewind() restarts (only before iteration begins). With these methods you can drive a generator manually.

Sending values back with send()

The send($value) method sends a value back to the paused yield expression. yield not only produces a value, it can also receive one as an expression: $received = yield $value;.

This lets you set up two-way communication with the generator. In send('hello'), 'hello' becomes the result of the yield expression and execution advances to the next yield.

Exercise Drive the generator manually

Create a generator with $gen = countUp(5, 8). Inside a while ($gen->valid()) loop, print the value with current(), then advance with next().

Show example solution

Set up a while ($gen->valid()) loop. Inside it, print the value with echo $gen->current() . "\n"; then advance with $gen->next();.
Example solution:
<?php
function countUp(int $from, int $to): \Generator {
    for ($i = $from; $i <= $to; $i++) {
        yield $i;
    }
}

$gen = countUp(5, 8);

while ($gen->valid()) {
    echo $gen->current() . "\n";
    $gen->next();
}

Test yourself

Get the first value with current()

$gen = countUp(1, 3);
echo $gen->____();

Show answer

$gen = countUp(1, 3);
echo $gen->current();

What does the send() method do?
- Sends a value to the generator, becomes the result of the yield expression
- Restarts the generator from the beginning
- Permanently closes the generator
- Only returns the next value, without sending anything
Show answer

Sends a value to the generator, becomes the result of the yield expression — Correct. send($value) advances from the paused yield, passing $value as the result of the yield expression.
Match the generator methods

current()

Returns the current yield value
next()

Advances to the next yield
valid()

Checks if more values remain
send()

Sends a value back to yield

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The Generator class