Editing Reference counting (section)

===Tcl===
[[Tcl]] 8 uses reference counting for memory management of values (Tcl Obj [[struct]]s). Since Tcl's values are immutable, reference cycles are impossible to form and no cycle detection scheme is needed. Operations that would replace a value with a modified copy are generally optimized to instead modify the original when its reference count indicates that it is not shared. The references are counted at a data structure level, so the problems with very frequent updates discussed above do not arise.