Test of PHP traits behavior using "self" and "static" keywords

trait_test.php

<?php declare(strict_types = 1);
// Tried on PHP 8.0.25

// Trait
trait TestTrait {
	public static function spawnSelf(): self {
		return new self();
	}
	
	public static function spawnStatic(): static {
		return new static();
	}
}


// Test classes
class TestClass {
	use TestTrait;
}

class TestClassChild extends TestClass {
	// The next line changes the behavior, see "Result #2".
	//use TestTrait;
}


// Util function
function class_str(object $class): string {
	return $class::class . PHP_EOL;
}


// Main code
echo 'TestClass::spawnSelf:   ' . class_str(TestClass::spawnSelf());
echo 'TestClass::spawnStatic: ' . class_str(TestClass::spawnStatic());

echo PHP_EOL;

echo 'TestClassChild::spawnSelf:   ' . class_str(TestClassChild::spawnSelf());
echo 'TestClassChild::spawnStatic: ' . class_str(TestClassChild::spawnStatic());



/*
>>> Result:
TestClass::spawnSelf:   TestClass
TestClass::spawnStatic: TestClass

TestClassChild::spawnSelf:   TestClass
TestClassChild::spawnStatic: TestClassChild


>>> Result #2:
// ...

TestClassChild::spawnSelf:   TestClassChild
TestClassChild::spawnStatic: TestClassChild
*/