Introducing built-in mutability entitlements

[SupunS]

Depends on #89

[dsainati1]

One other suggestion I had to improve this proposal would be to "break" the Mutable entitlement up a little bit more; instead of having one Mutable entitlement that allows any and all mutating operations on arrays and dictionaries, IMO we can have Insertable and Removable entitlements for these types, along with the Mutable entitlement. In this model the Mutable entitlement would allow access to any mutating function, but the Insertable would only allow inserting new values (while Removable would only allow removing). This doesn't need any support for "entitlement inheritance", as it can already be modeled today with entitlement sets; using type definitions for arrays like:

struct Array {
    access(all) let length: Int
    access(all)fun concat(_ array: T): T
    access(all) fun contains(_ element: T): Bool
    // ... other pub functions here 
    access(Mutable | Insertable) fun append(_ element: T): Void
    access(Mutable | Insertable) fun appendAll(_ array: T): Void
    access(Mutable | Insertable) fun insert(at: Int, _ element: T): Void
    
    access(Mutable | Removable) fun remove(at: Int): T
    access(Mutable | Removable) fun removeFirst(): T
    access(Mutable | Removable) fun removeLast(): T
 }

This way it will be possible to give someone only add/remove access to an array, while still also making it simple to give them full edit access as well.

[turbolent]

Great start! 👌

[turbolent]

👍 for the idea

We still might want to find consensus on the naming scheme. As Dete pointed out, it'll set a precedent, so we might want to discuss the naming scheme separately, as it also is a question/blocker for e.g. #92

[bjartek]

I think it is a good idea to discuss naming scheme in more general and just have a documented way on how it is done. Naming things is hard.

[turbolent]

@SupunS given the alignment on naming in #86 (comment), maybe the proposed entitlements should be renamed to Insert, Remove, and Mutate?

Also, is setting with indexing going to require Insert | Mutate?

[SupunS]

given the alignment on naming in #86 (comment), maybe the proposed entitlements should be renamed to Insert, Remove, and Mutate?

Yea, I was waiting till we reach a conclusion to update the naming. Will update once we have a consensus (looks like we are almost there).

Also, is setting with indexing going to require Insert | Mutate?

Yes, this is explained in assigment section

[turbolent]

👍

[turbolent]

@SupunS Approved in the Cadence Language Design Meeting, let's merge this FLIP and the implementation 👏 🎉