Editing Reference counting (section)

===Delphi===
<!-- this needs a rewrite it takes no account whatsoever of the history of the language! [[User:Plugwash|Plugwash]] 02:00, 24 June 2005 (UTC)-->
[[Delphi (programming language)|Delphi]] is mostly not a garbage collected language, in that user-defined types must still be manually allocated and deallocated; however, it does provide automatic collection using reference counting for a few built-in types, such as strings, [[dynamic array]]s, and interfaces<!--i'd hardly call interfaces a built in type [[User:Plugwash|Plugwash]] 02:00, 24 June 2005 (UTC)-->, for ease of use and to simplify the generic database functionality. It is up to the programmer to decide whether to use the built-in types; Delphi programmers have complete access to low-level memory management like in C/C++. So all potential cost of Delphi's reference counting can, if desired, be easily circumvented.

Some of the reasons reference counting may have been preferred to other forms of garbage collection in Delphi include:

* The general benefits of reference counting, such as prompt collection.
* Cycles either cannot occur or do not occur in practice because none of the garbage-collected built-in types are recursive. (using interfaces one could create such scenario, but that is not common usage)
* The overhead in code size required for reference counting is very small (on native x86, typically a single LOCK INC, LOCK DEC or LOCK XADD instruction, which ensures atomicity in any environment), and no separate thread of control is needed for collection as would be needed for a tracing garbage collector.
* Many instances of the most commonly used garbage-collected type, the string, have a short lifetime, since they are typically intermediate values in string manipulation. A lot of local string usage could be optimized away, but the compiler currently doesn't do it.
* The reference count of a string is checked before mutating a string. This allows reference count 1 strings to be mutated directly whilst higher reference count strings are copied before mutation. This allows the general behaviour of old style pascal strings to be preserved whilst eliminating the cost of copying the string on every assignment. 
* Because garbage-collection is only done on built-in types, reference counting can be efficiently integrated into the library routines used to manipulate each datatype, keeping the overhead needed for updating of reference counts low. Moreover, a lot of the runtime library is in hand-optimized assembler.
* The string type can be cast to a pointer to char, and high performance operations can be performed that way. This is important since both Delphi and FPC implement their RTL in Pascal. Various other automated types have such casting options.