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Generator::getReturn

(PHP 7, PHP 8)

Generator::getReturnGet the return value of a generator

Description

public Generator::getReturn(): mixed

Parameters

This function has no parameters.

Return Values

Returns the generator's return value once it has finished executing.

Examples

Example #1 Generator::getReturn() example

<?php

$gen
= (function() {
yield
1;
yield
2;

return
3;
})();

foreach (
$gen as $val) {
echo
$val, PHP_EOL;
}

echo
$gen->getReturn(), PHP_EOL;

The above example will output:

1
2
3

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User Contributed Notes 4 notes

up
15
pemapmodder1970 at gmail dot com
6 years ago
The note by jm at guide42 dot com is inaccurate. Generator::getReturn() does not check the existence of the return statement, but rather whether the function has returned (finished executing).

<?php
function f(){
yield;
}

f()->getReturn(); // Exception: Cannot get return value of a generator that hasn't returned

$f = f();
$f->next(); // NULL
$f->getReturn(); // NULL, because having no return statement implies an empty `return;`, and the void return value is resolved to null.
up
1
Hayley Watson
5 years ago
Just to be clear, the value returned by a generator is not yielded while it is running, but is available afterwards through the getReturn() method.

One use for this could be to record the output of a generator so that it can be iterated over again without having to reconstruct and re-run the generator. (Indeed, one could write a generator that simply does exactly this for any given iterable.)

<?php
function generate_squares($n)
{
$record = [];
for(
$i = 0; $i <= $n; ++$i)
{
yield (
$record[] = $i * $i);
}
return
$record;
}

$squares = generate_squares(10);
foreach(
$squares as $s)
{
echo
$s, ' ';
}
$recorded = $squares->getReturn();
echo
"\nThat's [", join(', ', $recorded), "]";
?>

Recording keys as well would take a bit more work, as generators are free to repeat them but arrays aren't.
up
0
brandon at cryy dot com
6 years ago
I'm not quite sure -- I feel there is an ambiguity issue here with returning a value inside a generator and ->getReturn() method of such generator as I have been able to return an array of sorts, something like this:

function dequeue(){
try{
foreach($this->buffer->data as $data){ ... }
}
return $statistics;
}

foreach(($generator = $this->dequeue()) as $bdata){
.....
}

if($statistics = $generator->getReturn()){
// generator returns $statistics
}

Obviously this is not a complete example, but $statistics does become available with the returned array.
up
-12
jm at guide42 dot com
7 years ago
Be careful that `->getReturn()` will throw an exception if no return is present in the generator:

<?php
function g() {
yield
'A';
}
try {
g()->getReturn();
} catch (
Exception $ex) {
var_dump($ex->getMessage());
// Cannot get return value of a generator that hasn't returned
}
?>
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