Generator::send

(PHP 5 >= 5.5.0, PHP 7, PHP 8)

Generator::sendEnvia um valor ao gerador

Descrição

public Generator::send(mixed $value): mixed

Envia o valor informado ao gerador como resultado da expressão yield corrente e retorna a execução do gerador.

Se o gerador não estiver na expressão yield quando o método for chamado, primeiro será deixado avançar para a primeira expressão yield antes de enviar o valor. Assim como não é necessário "forçar" os geradores do PHP com uma chamada ao método Generator::next() (como é feito em Python).

Parâmetros

value

Valor a ser enviado ao gerador. Este valor será o retornado pela expressão yield em que o gerador estiver.

Valor Retornado

Retorna o valor gerado.

Exemplos

Exemplo #1 Usando o método Generator::send() para injetar valores

<?php
function printer() {
echo
"Valor inicial.".PHP_EOL;
while (
true) {
$string = yield;
echo
$string.PHP_EOL;
}
}

$printer = printer();
$printer->send('Envio 1.');
$printer->send('Envio 2.');
?>

O exemplo acima produzirá:

Valor inicial.
Envio 1.
Envio 2.

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User Contributed Notes 6 notes

up
62
sfroelich01 at sp dot gm dot ail dot am dot com
10 years ago
Reading the example, it is a bit difficult to understand what exactly to do with this. The example below is a simple example of what you can do this.

<?php
function nums() {
    for (
$i = 0; $i < 5; ++$i) {
               
//get a value from the caller
       
$cmd = (yield $i);
       
        if(
$cmd == 'stop')
            return;
//exit the function
       
}    
}

$gen = nums();
foreach(
$gen as $v)
{
    if(
$v == 3)//we are satisfied
       
$gen->send('stop');
   
    echo
"{$v}\n";
}

//Output
0
1
2
3
?>
up
9
sergei dot solomonov at gmail dot com
10 years ago
<?php
function foo() {
   
$string = yield;
    echo
$string;
    for (
$i = 1; $i <= 3; $i++) {
        yield
$i;
    }
}

$generator = foo();
$generator->send('Hello world!');
foreach (
$generator as $value) echo "$value\n";
?>

This code falls with the error:
PHP Fatal error:  Uncaught exception 'Exception' with message 'Cannot rewind a generator that was already run'.
foreach internally calls rewind, you should remember this!
up
1
baohx2000 at gmail dot com
4 years ago
I have found that inverse generators (using $x = yield) is a great way to handle chunked batch processing. As data is being iterated, once a specific count has been fed to the generator, it processes and resets the data. For example, you could do a batch mysql insert every 500 records.

Example (note the handling of null, which you would send to the generator to handle stragglers after the previous batch)

function importer()
{
  $max = 500;
  $items = [];
  while (true) {
    $item = yield;
    if ($item !== null) {
      $items[] = yield;
    }
    if ($item === null || count($items) >= $max) {
       // do batch operations
       $items = [];
    }
  }
}
up
1
anonymous at example dot com
4 years ago
As of 7.3, the behavior of a generator in a foreach loop depends on whether or not it expects to receive data. Relevant if you are experiencing "skips".

<?php
class X implements IteratorAggregate {
    public function
getIterator(){
        yield from [
1,2,3,4,5];
    }
    public function
getGenerator(){
        foreach (
$this as $j => $each){
            echo
"getGenerator(): yielding: {$j} => {$each}\n";
           
$val = (yield $j => $each);
            yield;
// ignore foreach's next()
           
echo "getGenerator(): received: {$j} => {$val}\n";
        }
    }
}
$x = new X;

foreach (
$x as $i => $val){
    echo
"getIterator(): {$i} => {$val}\n";
}
echo
"\n";

$gen = $x->getGenerator();
foreach (
$gen as $j => $val){
    echo
"getGenerator(): sending:  {$j} => {$val}\n";
   
$gen->send($val);
}
?>

getIterator(): 0 => 1
getIterator(): 1 => 2
getIterator(): 2 => 3
getIterator(): 3 => 4
getIterator(): 4 => 5

getGenerator(): yielding: 0 => 1
getGenerator(): sending:  0 => 1
getGenerator(): received: 0 => 1
getGenerator(): yielding: 1 => 2
getGenerator(): sending:  1 => 2
getGenerator(): received: 1 => 2
getGenerator(): yielding: 2 => 3
getGenerator(): sending:  2 => 3
getGenerator(): received: 2 => 3
getGenerator(): yielding: 3 => 4
getGenerator(): sending:  3 => 4
getGenerator(): received: 3 => 4
getGenerator(): yielding: 4 => 5
getGenerator(): sending:  4 => 5
getGenerator(): received: 4 => 5
up
1
php at didatus dot de
2 years ago
If you want to use generator::send() within a foreach loop, you will most likely get an unexpected result. The Generator::send() method resumes the generator, which means the pointer within the generator is moved to the next element in the generator list.

Here is an example:

<?php

class ApiDummy
{
    private static
$apiDummyData = ['a', 'b', 'c', 'd', 'e'];

    public static function
getAll(): Generator {
        foreach (
self::$apiDummyData as $entry) {
            echo
'yielding $elem' . PHP_EOL;
           
$newElem = (yield $entry);
            echo
'yield return: ' . $newElem . PHP_EOL;
        }
    }
}

$generator = ApiDummy::getAll();

// example iteration one with unexpected result
foreach ($generator as $elem) {
    echo
'value from generator: ' . $elem . PHP_EOL;
   
$generator->send($elem . '+');
}

// example iteration two with the expected result
while ($generator->valid()) {
   
$elem = $generator->current();
    echo
'value from generator: ' . $elem . PHP_EOL;
   
$generator->send($elem . '+');
}
?>

The result of example iteration one:
yielding $elem
value from generator: a
yield return: a+
yielding $elem
yield return:
yielding $elem
value from generator: c
yield return: c+
yielding $elem
yield return:
yielding $elem
value from generator: e
yield return: e+

As you can see, the values b and d are not printed out and also not extended by the + sign.
The foreach loop receives the first yield and the send call causes a second yield within the first loop. Therefor the second loop already receives the third yield and so on.

To avoid this, one solution could be to use a while loop and the Generator::send() method to move the generator cursor forward and the Generator::current() method to retrieve the current value. The loop can be controlled with the Generator::valid() method which returns false, if the generator has finished. See example iterator two.

The expected result of example iteration two:
yielding $elem
value from generator: a
yield return: a+
yielding $elem
value from generator: b
yield return: b+
yielding $elem
value from generator: c
yield return: c+
yielding $elem
value from generator: d
yield return: d+
yielding $elem
value from generator: e
yield return: e+
up
-11
kexianbin at diyism dot com
8 years ago
an example:

$coroutine=call_user_func(create_function('', <<<'fun_code'
    echo "inner 1:\n";
    $rtn=(yield 'yield1');
    echo 'inner 2:';var_export($rtn);echo "\n";
    $rtn=(yield 'yield2');
    echo 'inner 3:';var_export($rtn);echo "\n";
    $rtn=(yield 'yield3');
    echo 'inner 4:';var_export($rtn);echo "\n";
fun_code
));
echo ":outer 1\n";                                       // :outer 1
var_export($coroutine->current());echo ":outer 2\n";     // inner 1:, 'yield1':outer 2
var_export($coroutine->current());echo ":outer 3\n";     // 'yield1':outer 3
var_export($coroutine->next());echo ":outer 4\n";        // inner 2:NULL, NULL:outer 4
var_export($coroutine->current());echo ":outer 5\n";     // 'yield2':outer 5
var_export($coroutine->send('jack'));echo ":outer 6\n";  // inner 3:'jack', 'yield3':outer 6
var_export($coroutine->current());echo ":outer 7\n";     // 'yield3':outer 7
var_export($coroutine->send('peter'));echo ":outer 8\n"; // inner 4:'peter', NULL:outer 8
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