Man modifiers

From LSWiki

Description

A modifier changes the syntactic and/or semantic behaviour of an object-global variable or a function in an object. The existing modifiers are described below. To use a modifier just prepend it to the declaration. If several modifiers are to be used their order does not matter:

 private int bar;                         // example for a variable
 protected nomask int foo() { return 3; } // example for a function

For functions:

• private -- such functions can only be called with an internal

call from within this file. Not even inheriting objects can call these functions. You can nevertheless build an lfun-closure with #' out of a private function.

• protected -- such functions can be called from within the object,

or from inheriting objects; but in neither case with call_other(). It is possible to create #' closures or use symbol_function() from within the object. Its use is preferred over the older "static".

• static -- such functions can be called from within the object

in either way (internal call or with call_other()). Inheriting objects can call such functions. But it is not possible to call static functions from other objects via call_other(). Note that an add_action() is treated like a call from within the object except the player who got the add_action() was forced (thus it is a simple way to secure an add_action() against forces, although this method has the severe disadvantages of raising an error at the force so better use the security system). Also efuns like call_out() or input_to() can call these functions if given as a string.

• public -- this is the default type. Such functions can be called

from within the file as well as from inheriting objects and other objects via call_other(). To declare a function public only results in the impossibility to change the accessibility at the inherit statement (see below). No error will occur, only the type will not be modified by the inherit statement.

• nomask -- such functions cannot be overridden by inheriting

objects. If you have the fun foo() defined in your object and inherit an object which also has declared a function foo() and this nomask, you will get an compile error if you try to load your object. Furthermore a shadow will fail if it tries to shadow a nomask declared function.

• varargs -- this changes the syntax of the function in a way that

not all of the arguments in the declaration must be given at the call. This is often very usefull if some of the arguments shall be omitable (the omitted arguments are set to 0 if the function is called with fewer arguments than specified). This is mainly within the object really necessary; call_other()s usually (that is if they do not have a certain pragma ('man pragma')) do not need the called function to be declared varargs to omit any arguments, but it is good style to use this modifier to document the code by this.

For object-global variables:

• private -- such variables can only be accessed from within the

same object. Not even inheriting objects can access private variables. It is a good style to declare all internal variables private to prevent inheriting objects from accessing the variables directly without using functions.

• nosave -- such variables are neither stored with save_object()

nor restored with restore_object(). This can be very useful if you want a room to use save_object() and restore_object() to save your own defined variables but not the hundreds of variables inherited from a room-class (e.g. /complex/room). You then use the modifier at the inherit statement (see below). Note that nosave and private do not overlap in any way. They are absolutely independent. The driver may be compiled to not recognize this keyword ('static' is then to be used). If 'nosave' is available, the macro __LPC_NOSAVE__ is defined.

• static -- the old name for 'nosave'. Its use is deprecated.

• public -- declares the variable public. It cannot be declared

private or static by inheriting. No error will occur, only the type will not be modified by the inherit statement.

It is not good style to let inheriting objects have access to internal variables so declare them as private and offer functions to query and change the variables if possible.

It is also possible to redeclare all variables and/or functions of an inherited object for the own object at the inheriting statement:

private functions nosave variables inherit "complex/room";
public variables inherit "complex/room";
private functions inherit "complex/room";

To redeclare a function or a variable declared public in the inherited object to be private or protected is not possible.

There also exists a modifier explicitly for the inherit statement:

• virtual -- inherits the given object virtually. This only makes

sense in a complex inherit tree. If an object is inherited normally (not virtually) twice somewhere in the inherit tree the intern variables exist twice. If inherited virtually they exist only once.

Example:

            A inherits B and C.
            B inherits D.
            C inherits D.
            If the inheritance of D is virtual in B and C
            D's variables exist only once in A. If A changes
            D's variables via functions of B this also changes
            the variables of D as known by C.

            virtual:               non-virtual:
               A                        A
              / \                      / \
             B   C                    B   C
              \ /                     |   |
               D                      D   D

To simplify the adoption of existing code, LPC allows to specify a default visibility for functions and variables, using a syntax similar to the inherit syntax:

 default private;

All variables and functions are by default private.

 default private variables public functions;

All variables are by default private, but functions are public.

Only the modifiers 'private', 'public' and 'protected' (and 'static' for functions only) are allowed here.

The default visibility thus set affects only variables/functions with no explicite visibility:

 default private;

 int private_var;
 public int public_var;

The definition is valid from the point of the 'default' statement until the end of the file, or until the next 'default' statement:

 default private;
 int private_var;

 default public;
 int public_var;

Note that this default visibility does not affect inherits.

History

The modifier 'static' for variables was renamed to 'nosave' with LDMud 3.2.8. 'static' is still recognized as an alias.

The default visibility was added in LDMud 3.2.9 as experimental feature.

See Also

closures(LPC), inheritance(LPC), functions(LPC), types(LPC)