In PHP, use the yield keyword to make the function return to the generator. 1. Using yield in the function will automatically become a generator function and return the Generator object; 2. The final value can be set through return and obtained with getReturn(); 3. PHP 8.1 can explicitly declare the return type as Generator; 4. Use yield from to call multiple generators nested. These features make the creation and management of generators more convenient.
In PHP, if you want to return a generator from a function, it is not complicated. The generator of PHP is based on Generator class and implements lazy evaluation through yield keyword. As long as your function uses yield , it will automatically become a generator function, and the return is also a Generator object.
Here are some specific usages and details that you may be concerned about:
How to write a function that returns a Generator
The easiest way is to use yield in the function. There is no need to explicitly declare the return type as Generator , although you can add comments or use PHP 8's union type feature to enhance readability.
function getNumbers() {
yield 1;
yield 2;
yield 3;
} When this function is called, it will not execute the code inside immediately, but will return a Generator instance:
$gen = getNumbers();
foreach ($gen as $number) {
echo $number;
}Note: Once you have traversed the generator once, you can't reuse it anymore. If you need to use it again, you must call the function again to create a new generator.
Use return to return the final value in the generator
The generator function can also have a return statement, but its function is not to return the result of the entire generator, but to obtain this value through Generator::getReturn() after the traversal is over.
function countToThree() {
yield 1;
yield 2;
yield 3;
return "Done counting";
}
$gen = countToThree();
foreach ($gen as $value) {
echo $value;
}
echo $gen->getReturn(); // Output: Done countingThis can be useful when you need to do some finishing work or record status.
Return Generator from explicit declaration of function (PHP 8.1)
If you want to express your intent more clearly, you can explicitly specify the return type as Generator in the function definition:
function getNumbers(): Generator {
yield 1;
yield 2;
yield 3;
}This helps static analysis tools to check types and improves code readability.
Nested calls to multiple generators
Sometimes you might want to "expand" the contents of another generator in one generator. You can use yield from :
function generateA() {
yield 'a';
yield 'b';
}
function generateAll() {
yield from generateA();
yield 'c';
yield 'd';
}
foreach (generateAll() as $char) {
echo $char; // output abcd
}This approach allows you to organize multiple generator logic while keeping each function single.
Basically that's it. As long as you use yield , PHP will automatically handle the creation and management of the generator, without the need for additional new or return specific objects.
The above is the detailed content of How to return a Generator from a PHP function?. For more information, please follow other related articles on the PHP Chinese website!
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