Callback functions used to overload various builtin functions.

The functions can be grouped into a few sets:

• Object initialization and destruction.

  __INIT(), create(), destroy()

• Unary operator overloading.

  `~(), `!(), _values(), cast(), _sizeof(), _indices(), __hash()

• Binary asymmetric operator overloading.

  `+(), ``+(), `-(), ``-(), `&(), ``&(), `|(), ``|(), `^(), ``^(), `<<(), ``<<(), `>>(), ``>>(), `*(), ``*(), `/(), ``/(), `%(), ``%()

• Binary symmetric operator overloading.

  The optimizer will make assumptions about the relations between these functions.

  `==(), _equal(), `<(), `>()

• Other binary operator overloading.

  `[](), `[]=(), `->(), `->=(), `+=(), `()()

• Overloading of other builtin functions.

  _is_type(), _sprintf(), _m_delete(), _get_iterator(), _search()

Although these functions are called from outside the object they exist in, they will still be used even if they are declared protected. It is in fact recommended to declare them protected, since that will hinder them being used for other purposes.

::

void __INIT()

Inherit and variable initialization.

This function is generated automatically by the compiler. It's called just before lfun::create() when an object is instantiated.

It first calls any __INIT functions in inherited classes (regardless of modifiers on the inherits). It then executes all the variable initialization expressions in this class, in the order they occur.

This function can not be overloaded or blocked from executing.

lfun::create()

int __hash()

Hashing callback.

The main caller of this function is predef::hash_value() or the low-level equvivalent, which get called by various mapping operations when the object is used as index in a mapping.

It should return an integer that corresponds to the object in such a way that all values which lfun::`== considers equal to the object get the same hash value.

The function predef::hash does not return hash values that are compatible with this one.

It's assumed that this function is side-effect free.

lfun::`==, predef::hash_value()

void _deserialize(object o, function(function(mixed:void), string, type:mixed) deserializer)

Dispatch function for Serialization.deserialize().

Object to serialize. Always a context of the current object.

Function to be called once for every variable to serialize.

The deserializer function expects to be called with three arguments:

setter - Function that sets the symbol value.

symbol - The symbol name.

symbol_type - The type of the symbol.

A default implementation of lfun::_serialize() and lfun::_deserialize() is available in Serializer.Serializable.

lfun::_serialize(), Serializer.deserialize(), Serializer.Serializable()->_deserialize()

int _equal(mixed arg)

Recursive equality callback.

It's assumed that this function is side-effect free.

predef::equal(), lfun::`==()

predef::Iterator _get_iterator()

Iterator creation callback.

The returned predef::Iterator instance works as a cursor that references a specific item contained (in some arbitrary sense) in this one.

It's assumed that this function is side-effect free.

predef::Iterator, predef::get_iterator, predef::foreach()

array _indices(object|void context, int|void access)

List indices callback.

Expected to return an array with the valid indices in the object.

It's assumed that this function is side-effect free.

predef::indices(), lfun::_values(), lfun::_types(), ::_indices()

bool _is_type(string basic_type)

Type comparison callback.

Called by the cast operator to determine if an object simulates a basic type.

One of:

The following five shouldn't occurr, but are here for completeness:

Expected to return 1 if the object is to be regarded as a simulation of the type specified by basic_type.

The argument is currently a string with the name of the type, but might in the future be a value of the type type.

It's assumed that this function is side-effect free.

mixed _m_delete(mixed arg)

Delete index callback.

predef::m_delete()

mixed _random()

Called by random(). Typical use is when the object implements a ADT, when a call to this lfun should return a random member of the ADT or range implied by the ADT.

predef::random()

mixed _search(mixed needle, mixed|void start)

Search callback.

predef::search()

void _serialize(object o, function(mixed, string, type:void) serializer)

Dispatch function for Serializer.serialize().

Object to serialize. Always a context of the current object.

Function to be called once for every variable to serialize.

The serializer function expects to be called with three arguments:

value - The value of the symbol.

symbol - The symbol name.

symbol_type - The type of the symbol.

A default implementation of lfun::_serialize() and lfun::_deserialize() is available in Serializer.Serializable.

lfun::_deserialize(), Serializer.serialize(), Serializer.Serializable()->_serialize()

int _size_object()

Debug.size_object() callback.

Returns an approximation of the memory use in bytes for the object.

Debug.size_object(), lfun::_sizeof()

int _sizeof()

Size query callback.

Called by predef::sizeof() to determine the number of elements in an object. If this function is not present, the number of public symbols in the object will be returned.

Expected to return the number of valid indices in the object.

It's assumed that this function is side-effect free.

predef::sizeof()

string _sprintf(int conversion_type, mapping(string:int)|void params)

Sprintf callback.

This method is called by predef::sprintf() to print objects. If it is not present, printing of the object will not be supported for any conversion-type except for the %O-conversion-type, which will output "object".

One of:

Conversion parameters. The following parameters may be supplied:

Is expected to return a string describing the object formatted according to conversion_type.

_sprintf() is currently not called for the following conversion-types:

This function might be called at odd times, e.g. before lfun::create has been called or when an error has occurred. The reason is typically that it gets called when a backtrace is being formatted to report an error. It should therefore be very robust and not make any assumptions about its own internal state, at least not when conversion_type is 'O'.

It's assumed that this function is side-effect free.

predef::sprintf()

mixed _sqrt()

Called by sqrt when the square root of an object is requested.

_sqrt is not a real lfun, so it must not be defined as static.

predef::sqrt()

array _types(object|void context, int|void access)

List types callback.

This callback is typically called via predef::types().

Expected to return an array with the types corresponding to the indices returned by lfun::_indices().

It's assumed that this function is side-effect free.

predef::types() was added in Pike 7.9.

predef::types(), lfun::_indices(), lfun::_values(), ::_types()

array _values(object|void context, int|void access)

List values callback.

Expected to return an array with the values corresponding to the indices returned by lfun::_indices().

It's assumed that this function is side-effect free.

predef::values(), lfun::_indices(), lfun::_types(), ::_values()

int `!()

Logical not callback.

Returns non-zero if the object should be evaluated as false, and 0 (zero) otherwise.

It's assumed that this function is side-effect free.

predef::`!()

mixed `%(zero ... args)

Left side modulo callback.

It's assumed that this function is side-effect free.

lfun::``%(), predef::`%()

mixed `&(zero ... args)

Left side bitwise and/intersection callback.

It's assumed that this function is side-effect free.

lfun::``&(), predef::`&()

mixed `()(zero ... args)

Apply callback.

predef::`()

mixed `*(zero ... args)

Left side multiplication/repetition/implosion callback.

It's assumed that this function is side-effect free.

lfun::``*(), predef::`*()

mixed `+(zero arg, zero ... rest)

Left side addition/concatenation callback.

This is used by predef::`+. It's called with any arguments that follow this object in the argument list of the call to predef::`+. The returned value should be a new instance that represents the addition/concatenation between this object and the arguments in the order they are given.

It's assumed that this function is side-effect free.

lfun::``+(), lfun::`+=(), predef::`+()

this_program `+=(zero arg, zero ... rest)

Destructive addition/concatenation callback.

This is used by predef::`+. It's called with any arguments that follow this object in the argument list of the call to predef::`+. It should update this object to represent the addition/concatenation between it and the arguments in the order they are given. It should always return this object.

This function should only be implemented if lfun::`+() also is. It should only work as a more optimized alternative to that one, for the case when it's safe to change the object destructively and use it directly as the result.

This function is not an lfun for the += operator. It's only whether or not it's safe to do a destructive change that decides if this function or lfun::`+() is called; both the + operator and the += operator can call either one.

lfun::`+(), predef::`+()

mixed `-(void|zero arg)

Negation and left side subtraction/set difference callback.

This is used by predef::`-. When called without an argument the result should be a new instance that represents the negation of this object, otherwise the result should be a new instance that represents the difference between this object and arg.

It's assumed that this function is side-effect free.

lfun::``-(), predef::`-()

mixed `->(string index, object|void context, int|void access)

Arrow index callback.

Symbol in context to access.

Context in the current object to start the search from. If UNDEFINED or left out, this_program::this is to be be used (ie start at the current context and ignore any overloaded symbols).

Access permission override. One of the following:

Returns the value at index if it exists, and UNDEFINED otherwise.

It's assumed that this function is side-effect free.

predef::`->(), ::`->()

mixed `->=(string index, zero value, object|void context, int|void access)

Arrow index assignment callback.

Symbol in context to change the value of.

The new value.

Context in the current object to start the search from. If UNDEFINED or left out, this_program::this is to be used (ie start at the current context and ignore any overloaded symbols).

Access permission override. One of the following:

This function is to index the current object with the string index, and set it to value.

Returns the set value.

predef::`->=(), ::`->=(), lfun::`[]=()

mixed `/(zero ... args)

Left side division/split callback.

It's assumed that this function is side-effect free.

lfun::``/(), predef::`/()

bool `<(mixed arg)

Less than test callback.

It's assumed that this function is side-effect free.

predef::`<()

mixed `<<(zero arg)

Left side left shift callback.

It's assumed that this function is side-effect free.

lfun::``<<(), predef::`<<()

bool `==(mixed arg)

Equality test callback.

If this is implemented it might be necessary to implement lfun::__hash too. Otherwise mappings might hold several objects as indices which are duplicates according to this function. Various other functions that use hashing also might not work correctly, e.g. predef::Array.uniq.

It's assumed that this function is side-effect free.

predef::`==(), lfun::__hash

bool `>(mixed arg)

Greater than test callback.

It's assumed that this function is side-effect free.

predef::`>()

mixed `>>(zero arg)

Left side right shift callback.

It's assumed that this function is side-effect free.

lfun::``>>(), predef::`>>()

mixed `[..](zero low, int low_bound_type, zero high, int high_bound_type)

Subrange callback.

It's assumed that this function is side-effect free.

predef::`[..]

mixed `[](zero arg1, zero|void arg2)

Indexing callback.

For compatibility, this is also called to do subranges unless there is a `[..] in the class. See predef::`[..] for details.

It's assumed that this function is side-effect free.

predef::`[](), predef::`[..]

mixed `[]=(zero arg1, zero arg2)

Index assignment callback.

predef::`[]=(), lfun::`->=()

mixed `^(zero ... args)

Left side exclusive or callback.

It's assumed that this function is side-effect free.

lfun::``^(), predef::`^()

mixed ``%(zero ... args)

Right side modulo callback.

It's assumed that this function is side-effect free.

lfun::`%(), predef::`%()

mixed ``&(zero ... args)

Right side bitwise and/intersection callback.

It's assumed that this function is side-effect free.

lfun::`&(), predef::`&()

mixed ``*(zero ... args)

Right side multiplication/repetition/implosion callback.

It's assumed that this function is side-effect free.

lfun::`*(), predef::`*()

mixed ``+(zero arg, zero ... rest)

Right side addition/concatenation callback.

This is used by predef::`+. It's called with any arguments that precede this object in the argument list of the call to predef::`+. The returned value should be a new instance that represents the addition/concatenation between the arguments in the order they are given and this object.

It's assumed that this function is side-effect free.

lfun::`+(), predef::`+()

mixed ``-(zero arg)

Right side subtraction/set difference callback.

This is used by predef::`-. The result should be a new instance that represents the difference between arg and this object.

It's assumed that this function is side-effect free.

lfun::`-(), predef::`-()

mixed ``/(zero ... args)

Right side division/split callback.

It's assumed that this function is side-effect free.

lfun::`/(), predef::`/()

mixed ``<<(zero arg)

Right side left shift callback.

It's assumed that this function is side-effect free.

lfun::`<<(), predef::`<<()

mixed ``>>(zero arg)

Right side right shift callback.

It's assumed that this function is side-effect free.

lfun::`>>(), predef::`>>()

mixed ``^(zero ... args)

Right side exclusive or callback.

It's assumed that this function is side-effect free.

lfun::`^(), predef::`^()

mixed ``|(zero ... args)

Right side bitwise or/union callback.

It's assumed that this function is side-effect free.

lfun::`|(), predef::`|()

mixed `|(zero ... args)

Left side bitwise or/union callback.

It's assumed that this function is side-effect free.

lfun::``|(), predef::`|()

mixed `~()

Complement/inversion callback.

It's assumed that this function is side-effect free.

predef::`~()

mixed cast(string requested_type)

Value cast callback.

Type to cast to.

Expected to return the object value-casted (converted) to the type described by requested_type.

The argument is currently a string with the name of the type, but might in the future be a value of the type type.

Currently casting between object types is a noop.

If the returned value is not deemed to be of the requested type a runtime error may be thrown.

It's assumed that this function is side-effect free.

void lfun:create(zero ... args)

Object creation callback.

This function is called right after lfun::__INIT().

args are the arguments passed when the program was called.

In Pike 7.2 and later this function can be created implicitly by the compiler using the new syntax:

class Foo(int foo) {
   int bar;
 }

In the above case an implicit lfun::create() is created, and it's equvivalent to:

class Foo {
   int foo;
   int bar;
   protected void create(int foo)
   {
     local::foo = foo;
   }
 }

lfun::__INIT(), lfun::destroy()

void destroy(void|int reason)

Object destruction callback.

This function is called right before the object is destructed. That can happen either through a call to predef::destruct(), when there are no more references to the object, or when the garbage collector discovers that it's part of a cyclic data structure that has become garbage.

A flag that tells why the object is destructed:

Objects are normally not destructed when a process exits, so destroy functions aren't called then. Use atexit to get called when the process exits.

Regarding destruction order during garbage collection:

If an object is destructed by the garbage collector, it's part of a reference cycle with other things but with no external references. If there are other objects with destroy functions in the same cycle, it becomes a problem which to call first.

E.g. if this object has a variable with another object which (directly or indirectly) points back to this one, you might find that the other object already has been destructed and the variable thus contains zero.

The garbage collector tries to minimize such problems by defining an order as far as possible:

• If an object A contains an lfun::destroy and an object B does not, then A is destructed before B.

• If A references B single way, then A is destructed before B.

• If A and B are in a cycle, and there is a reference somewhere from B to A that is weaker than any reference from A to B, then A is destructed before B.

• If a cycle is resolved according to the rule above by ignoring a weaker reference, and there is another ambiguous cycle that would get resolved by ignoring the same reference, then the latter cycle will be resolved by ignoring that reference.

• Weak references (e.g. set with predef::set_weak_flag()) are considered weaker than normal references, and both are considered weaker than strong references.

• Strong references are those from objects to the objects of their lexically surrounding classes. There can never be a cycle consisting only of strong references. (This means the gc never destructs a parent object before all children have been destructed.)

An example with well defined destruct order due to strong references:

class Super {
   class Sub {
     protected void destroy() {
       if (!Super::this)
         error ("My parent has been destructed!\n");
     }
   }
   Sub sub = Sub();
   protected void destroy() {
     if (!sub)
       werror ("sub already destructed.\n");
   }
 }

The garbage collector ensures that these objects are destructed in an order so that werror in Super is called and not error in Sub.

When the garbage collector calls lfun::destroy, all accessible non-objects and objects without destroy functions are still intact. They are not freed if the destroy function adds external references to them. However, all objects with lfun::destroy in the cycle are already scheduled for destruction and will therefore be destroyed even if external references are added to them.

The garbage collector had completely random destruct order in versions prior to 7.2.

lfun::create(), predef::destruct()

mixed lfun::symbol

Symbols implicitly inherited from the virtual base class.

These symbols exist mainly to simplify implementation of the corresponding lfuns.

lfun::

mixed _indices(object|void context, int|void access)

Context in the current object to start the list from. If UNDEFINED or left out, this_program::this will be used (ie start at the current context and ignore any overloaded symbols).

Access permission override. One of the following:

Builtin function to list the identifiers of an object. This is useful when lfun::_indices has been overloaded.

::_values(), ::_types(), ::`->()

mixed _types(object|void context, int|void access)

Context in the current object to start the list from. If UNDEFINED or left out, this_program::this will be used (ie start at the current context and ignore any overloaded symbols).

Access permission override. One of the following:

Builtin function to list the types of the identifiers of an object. This is useful when lfun::_types has been overloaded.

::_indices(), ::_values(), ::`->()

mixed _values(object|void context, int|void access)

Context in the current object to start the list from. If UNDEFINED or left out, this_program::this will be used (ie start at the current context and ignore any overloaded symbols).

Access permission override. One of the following:

Builtin function to list the values of the identifiers of an object. This is useful when lfun::_values has been overloaded.

::_indices(), ::_types(), ::`->()

mixed `->(string index, object|void context, int|void access)

Builtin arrow operator.

Symbol in context to access.

Context in the current object to start the search from. If UNDEFINED or left out, this_program::this will be used (ie start at the current context and ignore any overloaded symbols).

Access permission override. One of the following:

This function indexes the current object with the string index. This is useful when the arrow operator has been overloaded.

::`->=()

void `->=(string index, mixed value, object|void context, int|void access)

Builtin arrow set operator.

Symbol in context to change the value of.

The new value.

Context in the current object to start the search from. If UNDEFINED or left out, this_program::this will be used (ie start at the current context and ignore any overloaded symbols).

Access permission override. One of the following:

This function indexes the current object with the string index, and sets it to value. This is useful when the arrow set operator has been overloaded.

::`->()