8. LFUN

  Namespace lfun::

    Description

      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()

    Note

      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.

    See also

      ::

    Method _sqrt

      `mixed _sqrt()`

    Description

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

    Note

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

    See also

      predef::sqrt()

    Method _random

      `mixed _random()`

    Description

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

    See also

      predef::random()

    Method __INIT

      `void __INIT()`

    Description

      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.

    Note

      This function can not be overloaded or blocked from executing.

    See also

      lfun::create()

    Method create

      `void lfun:(zero ... args)`

    Description

      Object creation callback.

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

      args are the arguments passed when the program was called.

    Note

      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;
           }
         }

  See also

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

  Method destroy

    `void destroy(void|int reason)`

  Description

    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.

  Parameter `reason`

    A flag that tells why the object is destructed:

    `Object.DESTRUCT_EXPLICIT` | Destructed explicitly by predef::destruct .
    `Object.DESTRUCT_NO_REFS` | Destructed due to running out of references.
    `Object.DESTRUCT_GC` | Destructed by the garbage collector.
    `Object.DESTRUCT_CLEANUP` | Destructed as part of the cleanup when the pike process exits. Occurs only if Pike has been compiled with the configure option `--with-cleanup-on-exit`. See note below.

  Note

    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.

  Note

    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`.

Note

  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.

Note

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

See also

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

Method `+

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

Description

  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.

Note

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

See also

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

Method `+=

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

Description

  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.

Note

  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.

Note

  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.

See also

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

Method ``+

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

Description

  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.

Note

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

See also

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

Method `-

  `mixed `-(void|zero arg)`

Description

  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 .

Note

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

See also

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

Method ``-

  `mixed ``-(zero arg)`

Description

  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.

Note

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

See also

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

Method `&

  `mixed `&(zero ... args)`

Description

  Left side bitwise and/intersection callback.

Note

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

See also

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

Method ``&

  `mixed ``&(zero ... args)`

Description

  Right side bitwise and/intersection callback.

Note

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

See also

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

Method `|

  `mixed `|(zero ... args)`

Description

  Left side bitwise or/union callback.

Note

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

See also

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

Method ``|

  `mixed ``|(zero ... args)`

Description

  Right side bitwise or/union callback.

Note

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

See also

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

Method `^

  `mixed `^(zero ... args)`

Description

  Left side exclusive or callback.

Note

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

See also

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

Method ``^

  `mixed ``^(zero ... args)`

Description

  Right side exclusive or callback.

Note

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

See also

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

Method `<<

  `mixed `<<(zero arg)`

Description

  Left side left shift callback.

Note

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

See also

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

Method ``<<

  `mixed ``<<(zero arg)`

Description

  Right side left shift callback.

Note

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

See also

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

Method `>>

  `mixed `>>(zero arg)`

Description

  Left side right shift callback.

Note

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

See also

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

Method ``>>

  `mixed ``>>(zero arg)`

Description

  Right side right shift callback.

Note

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

See also

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

Method `*

  `mixed `*(zero ... args)`

Description

  Left side multiplication/repetition/implosion callback.

Note

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

See also

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

Method ``*

  `mixed ``*(zero ... args)`

Description

  Right side multiplication/repetition/implosion callback.

Note

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

See also

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

Method `/

  `mixed `/(zero ... args)`

Description

  Left side division/split callback.

Note

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

See also

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

Method ``/

  `mixed ``/(zero ... args)`

Description

  Right side division/split callback.

Note

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

See also

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

Method `%

  `mixed `%(zero ... args)`

Description

  Left side modulo callback.

Note

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

See also

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

Method ``%

  `mixed ``%(zero ... args)`

Description

  Right side modulo callback.

Note

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

See also

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

Method `!

  `int `!()`

Description

  Logical not callback.

Returns

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

Note

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

See also

  predef::`!()

Method `~

  `mixed `~()`

Description

  Complement/inversion callback.

Note

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

See also

  predef::`~()

Method `==

  `int(0..1) `==(mixed arg)`

Description

  Equality test callback.

Note

  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 .

Note

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

See also

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

Method `<

  `int(0..1) `<(mixed arg)`

Description

  Less than test callback.

Note

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

See also

  predef::`<()

Method `>

  `int(0..1) `>(mixed arg)`

Description

  Greater than test callback.

Note

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

See also

  predef::`>()

Method __hash

  `int __hash()`

Description

  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.

Returns

  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.

Note

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

Note

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

See also

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

Method cast

  `mixed cast(string requested_type)`

Description

  Value cast callback.

Parameter `requested_type`

  Type to cast to.

Returns

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

Note

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

Note

  Currently casting between object types is a noop.

Note

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

Note

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

Method `[..]

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

Description

  Subrange callback.

Note

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

See also

  predef::`[..]

Method `[]

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

Description

  Indexing callback.

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

Note

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

See also

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

Method `[]=

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

Description

  Index assignment callback.

See also

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

Method `->

  `mixed `->(string arg)`

Description

  Arrow index callback.

Note

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

See also

  predef::`->()

Method `->=

  `mixed `->=(string arg1, zero arg2)`

Description

  Arrow index assignment callback.

See also

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

Method _sizeof

  `int _sizeof()`

Description

  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.

Returns

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

Note

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

See also

  predef::sizeof()

Method _indices

  `array _indices()`

Description

  List indices callback.

Returns

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

Note

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

See also

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

Method _values

  `array _values()`

Description

  List values callback.

Returns

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

Note

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

See also

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

Method `()

  `mixed `()(zero ... args)`

Description

  Apply callback.

See also

  predef::`()

Method _is_type

  `int(0..1) _is_type(string basic_type)`

Description

  Type comparison callback.

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

Parameter `basic_type`

  One of:

  `"array"`
  `"float"`
  `"function"`
  `"int"`
  `"mapping"`
  `"multiset"`
  `"object"`
  `"program"`
  `"string"`
  `"type"`
  `"void"`
  `"zero"`

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

  `"lvalue"`
  `"mapping_data"`
  `"object storage"`
  `"pike_frame"`
  `"unknown"`

Returns

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

Note

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

Note

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

Method _sprintf

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

Description

  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"`.

Parameter `conversion_type`

  One of:

  `'b'` | Signed binary integer.
  `'d'` | Signed decimal integer.
  `'u'` | Unsigned decimal integer.
  `'o'` | Signed octal integer.
  `'x'` | Lowercase signed hexadecimal integer.
  `'X'` | Uppercase signed hexadecimal integer.
  `'c'` | Character. If a fieldsize has been specified this will output the low-order bytes of the integer in network byte order.
  `'f'` | Float.
  `'g'` | Heuristically chosen representation of float.
  `'G'` | Like `%g`, but uses uppercase `E` for exponent.
  `'e'` | Exponential notation float.
  `'E'` | Like `%e`, but uses uppercase `E` for exponent.
  `'s'` | String.
  `'O'` | Any value (debug style).
  `'t'` | Type of the argument.

Parameter `params`

  Conversion parameters. The following parameters may be supplied:

  `"precision" : int` | Precision.
  `"width" : int` | Field width.
  `"flag_left" : int(1..1)` | Indicates that the output should be left-aligned.
  `"indent" : int` | Indentation level in `%O`-mode.

Returns

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

Note

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

  `'F'` | Binary IEEE representation of float (`%4F` gives single precision, `%8F` gives double precision.)

Note

  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'`.

Note

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

See also

  predef::sprintf()

Method _equal

  `int _equal(mixed arg)`

Description

  Recursive equality callback.

Note

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

See also

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

Method _m_delete

  `mixed _m_delete(mixed arg)`

Description

  Delete index callback.

See also

  predef::m_delete()

Method _get_iterator

  `predef::Iterator _get_iterator()`

Description

  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.

Note

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

See also

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

Method _search

  `mixed _search(mixed needle, mixed|void start)`

Description

  Search callback.

See also

  predef::search()

Method `symbol

  `mixed `symbol()`
  `mixed `symbol()`

Description

  Variable retrieval callback (aka "getter").

Note

  Note that the `symbol` in the name can be any symbol.

Note

  This is not a true LFUN, since it is even more low level!

Note

  This function WILL be called even by inheriting programs when they attempt to access the variable named `symbol`.

See also

  lfun::`->symbol=() , lfun::`->()

Method `symbol=

  `void `symbol=(zero value)`
  `void `symbol=(zero value)`

Description

  Variable assignment callback (aka "setter").

Note

  Note that the `symbol` in the name can be any symbol.

Note

  This is not a true LFUN, since it is even more low level!

Note

  This function WILL be called even by inheriting programs when they attempt to set the variable named `symbol`.

See also

  lfun::`->symbol() , lfun::`->=()

Namespace ::

  Description

    Symbols implicitly inherited from the virtual base class.

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

  See also

    lfun::

  Method `->

    `mixed `->(string index)`

  Description

    Builtin arrow operator.

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

  See also

    ::`->=()

  Method `->=

    `void `->=(string index, mixed value)`

  Description

    Builtin arrow set operator.

    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.

  See also

    ::`->()

  Method _indices

    `mixed _indices()`

  Description

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

  See also

    ::_values, ::`->

  Method _values

    `mixed _values()`

  Description

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

  See also

    ::_indices, ::`->