PHP Generators: yield from and Delegation

The yield from expression forwards yields from another iterable and can return a nested generator return value.

The examples below begin with the core behavior, then move to an application-oriented use.

How PHP Generators: yield from and Delegation Works

The yield from expression forwards yields from another iterable and can return a nested generator return value.

Example 1: Basic Usage

This example uses a small input to make the main behavior visible.

<?php

function primaryData(): Generator { yield "one"; yield "two"; }
function allData(): Generator { yield from primaryData(); yield "three"; }
foreach (allData() as $item) { echo $item . " "; }

Output:

one two three 

The yield from expression forwards yields from another iterable and can return a nested generator return value.

Example 2: A Different Input

A different set of values shows the same operation in another situation.

<?php

function evenValues(): Generator { yield from [2, 4, 6]; }
function allValues(): Generator { yield 0; yield from evenValues(); }
print_r(iterator_to_array(allValues()));

Output:

Array
(
    [0] => 2
    [1] => 4
    [2] => 6
)

yield from inherits key behavior from the nested iterable; keys may conflict when collecting results.

Practical Example: Applying the Feature

This example shows an application-style use of the feature, with its surrounding setup visible.

<?php

function headerRows(): Generator { yield "name,price"; }
function dataRows(): Generator { yield "book,12"; yield "pen,3"; }
function allRows(): Generator { yield from headerRows(); yield from dataRows(); }
foreach (allRows() as $csvRow) { echo $csvRow . "\n"; }

Output:

name,price
book,12
pen,3

The code is shown for learning. Adjust the class names, inputs and error handling to suit your application.

Important Behavior and Edge Cases

• yield from inherits key behavior from the nested iterable; keys may conflict when collecting results.
• The yield from expression forwards yields from another iterable and can return a nested generator return value.
• Observe differences in empty inputs, invalid states and optional extension availability where relevant.

Comparison With Related Approaches

Common Beginner Mistakes

Key Takeaways

• The yield from expression forwards yields from another iterable and can return a nested generator return value.
• yield from inherits key behavior from the nested iterable; keys may conflict when collecting results.
• Use the example that matches the values, runtime version and dependencies in your application.

PHP Generators: yield from and Delegation is useful when its behavior matches the data structure and lifecycle of your PHP application. Choose it with a clear understanding of its preconditions and returned values.