CONCEPT
modifiers
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
(but you cannot save and restore it).
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().
The use of 'static' in new code is not recommended.
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.
visible -- 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().
public -- similar to "visible", but the declaration as "public"
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.
deprecated - Whenever this function is called, a warning is issued.
Usually this is done at compile-time. Exceptions are
call_others and symbol_function() which warn at run-time.
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 independant.
static -- the old name for 'nosave'. Its use is deprecated.
protected -- such variables can be accessed by inheriting
programs. There is little difference to the default
visibility ("visible"). Protected variables are
not seen by variable_exists() from other objects,
and this modifier can be detected with variable_list().
visible -- this is the default visibility. The variable can
accessed by inheriting programs.
public -- declares the variable public. It cannot be declared
protected, private or static by inheriting. No error
will occur, only the type will not be modified by the
inherit statement.
deprecated - Whenever this variable is used, a warning is issue.
Usually this is done at compile-time, but
symbol_variable() warns at run-time.
It is no 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.
Inheritance:
~~~~~~~~~~~~
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.
The following table shows the result of the combination of
visibility modifiers at the function declaration and inherit
statement:
Function | Inheritance modifiers
modifier | public | visible | static | protected | private
-----------+-----------+-----------+-----------+-----------+---------
public | public | public | public | public | public
visible | public | visible | static | protected | private
static | static | static | static | protected | private
protected | protected | protected | protected | protected | private
private | private | private | private | private | private
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', 'protected', 'visible' and 'public'
(and 'static' for functions only) are allowed here.
The default visibility thus set affects only variables/functions with
no explicit 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.
LDMud 3.5 introduced 'visible' as a name for the default
visibility.
SEE ALSO
closures(LPC), inheritance(LPC), functions(LPC), types(LPC)
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