[Collections] Add new error-friendly get equivalent

[drkameleon]

The main idea:

• it will work like get with blocks, dictionaries, etc
• if the requested index is not there, instead of throwing an error, it will return null
• suggested name: fetch
• usage case: x: (fetch d 'field) ?? "default"

[Eloitor]

why not get.default: null ?

[Eloitor]

x: get.default: "default" d 'field

[drkameleon]

why not get.default: null ?

Good point!

If it was a normal stdlib function, that could work.
The problem is get (and set) are used extensively and mostly auto-transformed at AST level (.field which we have recently added could be an exception, since it's for objects only).

But having to check if the attribute is there for normal array/dictionary access, apart from slow (performance-wise), it would be close to impossible... 😉

[Eloitor]

why not have get.default: in the stdlib, and transform it into a (hidden?) vm operation fetch when "compiling"?

[drkameleon]

why not have get.default: in the stdlib, and transform it into a (hidden?) vm operation fetch when "compiling"?

AST transformation generally plays with the main tree structure when doing its magic. But attributes are not included.
If they were, it would defeat the very cascade-style nature of attributes in Arturo...

I mean...

do.default [
    get ... ; is this a `get.default`? Could be, or could be not... we cannot know on the AST level
]

Technicalities aside, something that I actually wanted (probably for months lol) is a quick way to short-circuit a get, and that: x: (fetch d 'field) ?? "default" looks short enough...