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PHP: In PHP 5+, the destructor method has the name __destruct. There were no destructors in prior versions of PHP. [3] Python: there are __del__ methods called destructors by the Python 2 language guide, [4] but they are actually finalizers as acknowledged in Python 3. [5] Rust: the destructor method for rust has the name drop. [6]
The terminology of finalizer and finalization versus destructor and destruction varies between authors and is sometimes unclear.. In common use, a destructor is a method called deterministically on object destruction, and the archetype is C++ destructors; while a finalizer is called non-deterministically by the garbage collector, and the archetype is Java finalize methods.
In garbage-collected languages, such as Java, [4]: 26, 29 C#, [5]: 208–209 and Python, destructors are known as finalizers. They have a similar purpose and function to destructors, but because of the differences between languages that utilize garbage-collection and languages with manual memory management, the sequence in which they are called ...
Perl, Python (in the CPython implementation), [20] and PHP [21] manage object lifetime by reference counting, which makes it possible to use RAII. Objects that are no longer referenced are immediately destroyed or finalized and released, so a destructor or finalizer can release the resource at that time.
Aspects of object lifetime vary between programming languages and within implementations of a language. The core concepts are relatively common, but terminology varies. For example, the concepts of create and destroy are sometimes termed construct and destruct and the language elements are termed constructor (ctor) and destructor (dtor).
Also note the virtual destructors in the base classes, B1 and B2. They are necessary to ensure delete d can free up memory not just for D, but also for B1 and B2, if d is a pointer or reference to the types B1 or B2. They were excluded from the memory layouts to keep the example simple. [nb 2]
Sub Destructor() instructions End Sub: PHP function __construct(«parameters ... Python — PHP Perl Raku PRE {condition } POST {condition } Ruby — Windows PowerShell
The destructor receives the value associated with the key as parameter so it can perform cleanup actions (close connections, free memory, etc.). Even when a destructor is specified, the program must still call pthread_key_delete to free the thread-specific data at process level (the destructor only frees the data local to the thread).