Immutability vs. mutability

gistfile1.php

<?php

interface console
{
	function newData($data);
	function noMoreData();
	function dataGeneratorIs(dataGenerator $dataGenerator);
}

interface dataGenerator
{
	function consoleIs(console $console);
}

class mutableConsole implements console
{
	private
		$data
	;

	function newData($data)
	{
		$this->data .= $data;

		return $this;
	}

	function noMoreData()
	{
		echo $this->data . PHP_EOL;
	}

	function dataGeneratorIs(dataGenerator $dataGenerator)
	{
		$dataGenerator->consoleIs($this);

		return $this;
	}
}

class immutableConsole implements console
{
	private
		$data
	;

	function newData($data)
	{
		$console = new self;
		$console->data = $this->data . $data;

		return $console;
	}

	function noMoreData()
	{
		echo $this->data . PHP_EOL;
	}

	function dataGeneratorIs(dataGenerator $dataGenerator)
	{
		$dataGenerator->consoleIs($this);

		return $this;
	}
}

class numberGenerator implements dataGenerator
{
	function consoleIs(console $console)
	{
		foreach (range(1, 10) as $number)
		{
			$console->newData($number);
		}

		return $this;
	}
}

$numberGenerator = new numberGenerator;

(new mutableConsole)->dataGeneratorIs($numberGenerator)->noMoreData();

(new immutableConsole)->dataGeneratorIs($numberGenerator)->noMoreData();