first util to get the first item from the generator

[pjasiun]

It's basically generator.next().value;, but:

first( doc.selection.getSelectedBlocks() );

seems to be more readlable them:

doc.selection.getSelectedBlocks().next().value;

I know we have nth, but it's a common case when you wants to get the first value and we could have a dedicated method for it.

[Reinmar]

We've got nth() already, but I also see that first() is being the most popular use case in the normal code. nth() is mostly used in the tests.

[ma2ciek]

But similarly to nth() implementation the implementation of first() shouldn't change the iterator, right? (Like iterator.next().value does)

[pjasiun]

What do you mean? As far as I know nth() do change the iterator, but you can check it to be sure.

[ma2ciek]

I checked it and the nth( index, iterable ) function even finishes the iterator generator no matter what the index is, because every for of loop finishes the generator. So maybe the first( iterator ) function should run inside just nth( 0, iterator ) :D

[Reinmar]

Interesting... I'd love first() to work like shift() because subsequent first() calls may be a usecase one day. But nth() can read the entire iterable. It's even better if nth() reads the entire iterable, because then you'd have a better chance to notice that something went wrong (if you didn't know that it consumes the items)

[ma2ciek]

Ok. So the PR for the first() is ready and the missing parts are fixed. It works similar to the shift() for now. I'll report an issue for the nth() function improvement.

[Reinmar]

As I commented in ckeditor/ckeditor5-utils#130 I find my previous proposal totally wrong now. I take it back :P

[pjasiun]

If we want to pop the first value multiple times maybe we should have a better name, like pop or head (note that lodash use head and first is the alias for it https://lodash.com/docs/4.17.4#head)?

[Reinmar]

pop() means taking the last item. And I like first() more than head(). But I'm fine with both.