ImmutableClass.php

<?php

class ImmutableClass
{
  protected $property1;
  protected $property2;
  
  // Clone, set value, return the clone.
  public function withProperty1($value)
  {
    $clone = clone $this;
    $clone->property1 = $value;
    return clone;
  }

  // Same actions in one line using laravel tap.
  public function withProperty2($value)
  {
    return tap(clone $this, fn($clone) => $clone->property2 = $value);
  }
}

The laravel tap helper effectively does this:

1. Evaluates the first parameter.
2. Does something with it using the closure of the second parameter.
3. Returns the evaluated value, which mayt now be modified.

tap does not have to modify the value it is given. For example, this is given 1 and does nothing in the closure, so returns 1:

tap(1, fn() => null)

The return value of the closure does nothing. So this still returns 1 and not 2 as you may expect:

tap(1, fn($v) => ++$v)