Can anyone explain this array declaration to me?

Question

just wondering the difference between the presence of the last comma in the array, if there is any at all

>> [1,2,3]
=> [1, 2, 3]
>> [1,2,3,]
=> [1, 2, 3]

The second array still works, no exception raised

Thanks

• Daniel Daranas: I suggest that you edit the question title into something a bit more explanatory.
• Allen Rice: I cleaned it up for him a little

Answer 1

There's no difference. In Ruby, you're free to add a trailing comma to an array. It makes syntax like this:

a = [
 1,
 2,
 3,
]

A bit nicer, in some cases (e.g., if you want to add an element, you simply add a 4, line and don't have to worry about checking for a comma on the last line).

• Allen Rice: it doesn't add null or anything? Array length is the same w/ or w/o the comma?
• mipadi: No, no null value is added -- the array just contains the elements 1,2,3 in either case.
• penger: I guess there is no difference really eh? It really is just out of curiosity, I was coding and found something like this so I guess I would ask all you smart folks here.

Answer 2

It isn't a error, just a empty value(ignored by the compiler), but I suggest you to read Understanding Ruby Arrays

• Mladen Jablanović: Where exactly does that link mention optional trailing comma?

Answer 3

There is nothing special about arrays.

[1,2,3]

is the same as

Array.[](1,2,3)

so the values are just method call parameters. The same applies to

{a: 1, b: 2}

which is the same as

Hash.[](:a, 1, :b, 2)

And the reason trailing commas are allowed in method-call parameters is just because Ruby is designed like that, for the reasons of convenience that @mipadi mentioned.