Every time a new assignment or parameter passing is made, the reference count of the String has to be increased, this is an atomic lock, and is related to memory management, so it’s there whether you’re using simple reference-counting or copy-on-write.
Under a GC, no atomic lock is required, a simple reference (pointer) has to be copied. This is very efficient, locally, but the memory management costs are just deferred to a later garbage collection phase. Since immutable strings don’t have reference to other objects, the GC for them can theoretically happen in parallel without any drawbacks (assuming the GC supports it).
So under a GC, an immutable String type makes a whole lot of sense, as implementing a copy-on-write one requires a lot of effort, and a mutable one is problematic multi-threading wise.
https://www.delphitools.info/2013/05/13/immutable-strings-in-delphi/
#pascal #string #strings #immutable_string #delphi #gc #programming
