replace shallowCopy for ARC/ORC

[ringabout]

Hello, shallowCopy has been removed for ARC/ORC since it does a deep copy with ARC/ORC → nim-lang/Nim#20070

I don't know a good alternative for shallowCopy.

ref nim-lang/Nim#19972

[andreaferretti]

Hi @ringabout, thank you for the PR. But I must say I am confused - isn't there a mechanism to share storage with ORC? The whole point of the rotate function and RotatedString is to return something that behaves like a rotated string, but actually does not copy the whole memory.

[ringabout]

isn't there a mechanism to share storage with ORC?

Imo, strings and seqs cannot be shared with ARC/ORC in a safe way. It can be either moved or copied. Sometimes it can be optimized using sink, which let the compiler choose whether to copy or move.

[ghost]

I think the only workaround that can actually work in this case without changing semantics is creating some ref object type that stores the string internally (even though this will lead to double indirection which kinda sucks).

[planetis-m]

You could use a cow string implementation internally.

[andreaferretti]

I think I will go with double indirection as soon as I have time

[ringabout]

I think the only workaround that can actually work in this case without changing semantics is creating some ref object type that stores the string internally (even though this will lead to double indirection which kinda sucks).

I'm not sure how to achieve that while keeping this test work

proc rotate*(s: string, i: int): RotatedString
test "underlying strings are shared":
  var
    x = "Hello, world"
    y = x.rotate(5)

  y[0] = 'f'
  check x[5] == 'f'