[8.x] Add Collection@isSingle method

[JosephSilber]

Adds an isSingle method to the collections:

collect([])->isSingle();     // false
collect([1])->isSingle();    // true
collect([1, 2])->isSingle(); // false

Calling $collection->count() === 1 is so common, I believe it makes sense to have a separate expressive method for it (even more so for the lazy collection, which is a tad more tricky).

[gocanto]

why is take(2) necessary? :)

[JosephSilber]

@gocanto without it, the whole collection would have to be enumerated, which is a waste.

As soon as we know that there are 2, we know that it's not single!

---

See this test, which ensures we don't enumerate more than 2 items:

framework/tests/Support/SupportLazyCollectionIsLazyTest.php

Lines 487 to 492 in b72178d

	public function testIsSingleIsLazy()
	{
	$this->assertEnumerates(2, function ($collection) {
	$collection->isSingle();
	});
	}

Without take(2), this test would fail.

[gocanto]

cool stuff.

[browner12]

idk, seems like overkill to me.

if(collect([1])->count() === 1)) 

is super readable and pretty terse already.

[ahinkle]

Taylor updated this to containsOneItem(); 5b7ffc2

[stancl]

If you want syntax improvements to ->count() === $x why not go with ->countIs($x) or even ->count($x)

if ($collection->count() === 1)

if ($collection->countIs(1))

if ($collection->count(1))

if ($collection->isSingle())

if ($collection->containsOneItem())

containsOneItem() or isSingle() makes this work only for a single use case without really improving readability IMO

[LucaRed]

$collection->count() === 1;

$collection->containsOneItem();

Hmm. It's even longer than the normal comparison. I find it less readable.

+1 for a general method such as countIs($n).