Hash inside round brackets

Mateusz Leśniak when you use the equality operator = you're interacting with the array instance, not just with an element, so you need to tell Ruby that you want to make that variable an array by using the square brackets [].

If you just want to add an element, you need to push to that to the array, using the push method on the array instance. Since it's a method, it accepts the arguments in round brackets. In your example, you are pushing a hash.

Ruby's documentation on array is good in understanding how to create an array, add elements to it (push to that array), remove them and so on.

Sorry for not being more clear Mateusz.

I was talking about arrays because the push method is used for adding elements to arrays.

To initialize arrays you need to use square brackets [], for hashes you have the curly ones {}. Round brackets are only used for passing arguments to methods, so that's why you se them with the push method. That method knows you're passing a hash because it expects any kind of object and you're passing a key-value pair, which it's identified as a hash.

So to initialize the hash you need to do it like this:

hash = {description: "description"}

or

hash = {}
hash[:description] = "description"

Sorin, thank you for your answer, but my doubts are about hash, not array (or maybe you answerd me, but i don't really understand it yet). I'm wondering how ruby knows that it is hash inside round brackets, when we are pushing it inside an array, and ruby doesn't know if it is hash, when i'm trying to assign it to variable (also using round brackets and symbol as a key (key:value))