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Instantiation with a static Factory Method

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Ok people - the whole "dino park" idea - apparently, it's a huge success! Especially the velociraptors. Management wants us to grow more of them... a lot more. What could go wrong?

And because we're going to need to create velociraptors so often, passing that whole string to the constructor and then true is too much work... and spelling velociraptor is hard! So, idea time: what if we created a static factory method on Dinosaur to help us create them? Like a growVelociraptor() method! Hey! I just described some new behavior! Quick! To the example...mobile!

Telling phpspec to use a Factory Method

Add a new function: it_should_grow_a_large_velociraptor(). Oh, but this is tricky: we know how to control what arguments phpspec passes to the __construct() method when it creates the Dinosaur. But... in this case, we don't want phpspec to create the Dinosaur object on its own. Nope! We instead want phpspec to call our new static method and that will instantiate and return the Dinosaur.

... lines 1 - 9
class DinosaurSpec extends ObjectBehavior
{
... lines 12 - 69
function it_should_grow_a_large_velociraptor()
{
... lines 72 - 77
}
}

No problem: instead of beConstructedWith(), call $this->beConstructedThrough('growVelociraptor') - that will be the name of the new method. The second argument is the array of arguments for the method. What arguments should the growVelociraptor have? Hmm, probably just one right now: the length. So, array(5). If you need a second argument, just add another item.

... lines 1 - 69
function it_should_grow_a_large_velociraptor()
{
$this->beConstructedThrough('growVelociraptor', [5]);
... lines 73 - 77
}
... lines 79 - 80

Ok cool! Now this function will work like any other example - except that $this will be the Dinosaur object that's returned from growVelociraptor. Well, actually, we should make sure it is a Dinosaur: $this->shouldBeAnInstanceOf(Dinosaur::class). Oh, and how about $this->getGenus()->shouldBeAString(). Ok, I'm just showing you that this function exists. In this case, we know exactly that $this->getGenus()->shouldBe('Velociraptor').

... lines 1 - 69
function it_should_grow_a_large_velociraptor()
{
... lines 72 - 73
$this->shouldBeAnInstanceOf(Dinosaur::class);
$this->getGenus()->shouldBeString();
$this->getGenus()->shouldBe('Velociraptor');
... line 77
}
... lines 79 - 80

Wait, but why did I use shouldBe() here when we've been using shouldReturn() until now? No reason - they're identical: use whatever feels good.

Oh, and see how PhpStorm is highlighting getGenus()? That's because that method doesn't exist yet. We just "discovered" that we need this method. Cool! Let's add one more check: $this->getLength()->shouldBe(5).

... lines 1 - 69
function it_should_grow_a_large_velociraptor()
{
... lines 72 - 76
$this->getLength()->shouldBe(5);
}
... lines 79 - 80

You know the drill: after writing the example, run phpspec:

./vendor/bin/phpspec run

Honestly, it shouldn't even be a surprise any more when phpspec generates code for us. Choose "yes" so it generates the missing growVelociraptor() method. And when it re-executes... failure! A BadMethodCallException(). That comes from the new function. phpspec knows this should return a Dinosaur object... but it's not sure how. But hey! It did, once again, put this method in just the right place: below the constructor but above the public functions.

... lines 1 - 4
class Dinosaur
{
... lines 7 - 18
public static function growVelociraptor($argument1)
{
throw new \BadMethodCallException("Mismatch between the number of arguments of the factory method and constructor");
}
... lines 23 - 42
}

Change the argument to int $length, advertise that this will return an instance of self, and create that with $dinosaur = new static() passing Velociraptor and true for the isCarnivorous argument. Then, $dinosaur->setLength($length), return $dinosaur.

... lines 1 - 18
public static function growVelociraptor(int $length): self
{
$dinosaur = new static('Velociraptor', true);
$dinosaur->setLength($length);
return $dinosaur;
}
... lines 26 - 52

That felt good! Let's make sure the example passes:

./vendor/bin/phpspec run

Allowing Requirements to Emerge

Wait... it failed! Of course! The getGenus() method doesn't exist! That's super cool: instead of planning ahead and adding this method earlier, we allowed the need for this method to "emerge" naturally. What's especially interesting is that, so far, the only place we need this method is in our example! What if we don't need this method in our actual app? Should we still create it? Yes. Well, let me say that differently. The code in our examples are meant to be real examples of how you want your class to work. If you really don't want a getGenus() method, then should write example code that doesn't use it. If you do use it, you need it!

So, yes phpspec, please generate that for me. Find the new method, return $this->genus and add the string return type. Try the tests again:

... lines 1 - 46
public function getGenus(): string
{
return $this->genus;
}
... lines 51 - 52
./vendor/bin/phpspec run

Yes! All green! Next: as cool as this factory method is, we need to level up with a proper, new DinosaurFactory service class.

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