8.2 KiB
Method Definitions
Method definitions define functions within a structure or class that can be accessed directly within other methods of the object (or its derived classes,) or indirectly from instances of it with the member access operator.
Methods marked as virtual may have their functionality overridden by derived
classes, and in those overrides one can use the Super keyword to call the
parent function.
Methods are formed as so:
$[Method-definition-flags...]$ Type $[ , Type]$... Identifier ( $[Method-argument-list]$ ) $[ const ]$
{
$[Statement...]$
}
If const is placed after the function signature and before the function body,
the method will not be allowed to modify any members in the object instance
it's being called on.
The keyword void can be used in place of the return type (or type list) to
have a method which does not have any return value. Similarly, one can place
void where the argument list might be, although this is redundant as having
no argument list at all is allowed.
Arguments of methods may only be of certain types due to technical limitations. See the type table for a list of which are usable and which are not.
All methods which are not static have an implicit self parameter which
refers to this object, although if you wish to refer to a member of self, you
do not need to reference it directly, as it is already implicitly in scope.
Method Argument List
Method arguments must all have a name and type, and optionally the last
arguments in the list may have a default value, (Version 3.3.0 and newer)
except in functions marked override. The syntax is:
Type Variable-name $[ , Method-argument-list]$
Type Variable-name = Expression $[ , Method-argument-list]$
Or, the entire list may simply be void or empty.
Example: Method argument lists
// With the function:
void DoSomething(int one, int two, int a = 0, int b = 0);
// One could do the following:
DoSomething(4, 5);
DoSomething(5, 6, 7);
DoSomething(6, 7, 8, 9);
// Or using named default arguments,
DoSomething(5, 6, a: 7);
// Equivalent to:
DoSomething(5, 6, 7);
// And more examples:
DoSomething(6, 7, b: 8);
DoSomething(7, 8, a: 9, b: 10);
DoSomething(7, 8, 9, 10);
Method Definition Flags
| Flag | Description |
|---|---|
action ( Scope $[ , Scope]$... ) |
Same as action, but has specified action scopes. See "Action Scoping" for more information. |
action |
Method may have implicit invoker and stateinfo parameters. See below for more info. |
clearscope |
Method has Data scope. |
deprecated ( "ver" $[ , "reason" ]$ ) |
If accessed, a script warning will occur on load if the archive version is greater than ver, with the reason reason specified in the message. |
final |
Virtual method cannot be further overridden from derived classes. |
native |
Method is from the engine. Only usable internally. |
override |
Method is overriding a base class' virtual method. |
play |
Method has Play scope. |
private |
Method is not visible to any class but this one. |
protected |
Method is not visible to any class but this one and any descendants of it. |
static |
Function is not a method, but a global function without a self pointer. |
ui |
Method has UI scope. |
vararg |
Method doesn't type-check arguments after .... Only usable internally. |
version ( "ver" ) |
Restricted to ZScript version ver or higher. |
virtual |
Method can be overridden in derived classes. |
virtualscope |
Method has scope of the type of the object it's being called on. |
Action functions
ZScript includes an extra method type for descendents of Actor called
actions, which are intended to be run from actor states and give extra
information to the function. Action functions change the meaning of the self
parameter and may pass in invoker and stateinfo parameters as well. stateinfo
refers to the State which this action was called from.
Action scopes are a flag field and as such an action function can have multiple scopes.
The only scopes that actually set the internal action function flag are item, overlay and weapon,
so action functions without one of these do not act much like action functions, and they do not get an
invoker or stateinfo pointer.
Here is a chart for the meanings of the self and invoker variables under each scope.
Scopes lower down on the chart "override" scopes above them, so to speak:
| Scope | self meaning |
invoker meaning |
|---|---|---|
| None | The actor this function operates on, ambiguous in some contexts | N/A |
actor |
The actor | N/A |
item |
Context-dependent. The item itself when it exists in-world, but the owner when used as part of a CustomInventory state chain | Item itself |
overlay |
Context-dependent. The actor itself when it exists in-world, but the owner of the PSprite when it is being used as one | Context-dependent. The actor itself when it exists in-world, but the PSprite's caller field when it is being used as one. In most cases this field should be set to be the actor defining the action function, but it can be changed by user code so this is not technically guaranteed |
weapon |
Same as overlay, but self is allowed to be any subclass of Actor rather than just a subclass of the defining class |
Same as overlay |