Function
A function is something defined in code which carries out an instruction or set of instructions and may or may not have inputs and outputs. The builtin functions which are provided by the various games themselves are referred to as commands, and are called in a different manor to functions which are defined within scripts. Functions were first introduced in the OFP: Resistance patch.
Functions can also be used to reuse code. You can write some code once in the function and then include it in many different scripts. When the code is updated, it is updated for all scripts. When you only copy and paste the code to the other scripts, you have to update every script on any change.
Types of function
Functions-as-files
- See calling functions for how a function-as-file is called.
Functions as files are functions stored within a file. These are usually used for larger and more complex functions. The code is evaluated in the same way, however, there are additional commands which must include the file before the function itself can be called.
//MyFile.sqf // Code here..
Inline functions
Inline functions are functions are technically code which is often stored within a variable or declared as a function parameter. Inline functions operate the same way as functions-as-files as both are evaluated in the same way, but the difference is that inline functions are stored within parentheses{}, whereas functions-as-files do not require these.
//InlineFunction as Variable
MyVariableName ={
// Code here..
};
// InlineFunction as command/function parameter _myTemporaryVariable =player addEventHandler ["killed", {diag_log "I am providing an inline function (code) to this builtin command! Hurray for science!"}];
Anatomy of a function
When scripting, there are two types of functions: functions-as-files and inline functions. Functions-as-files are instances where the a whole file itself is used to house a function, whereas inline functions are either contained within a variable or as a parameter of a function. Some built-in functions require functions-as-files, whereas most will support both.
Parameters
Parameters for functions are available to the function via the magic variable _this. Declaration of parameters can be done using the params command. Common practice for defining parameters is done via the use of private variables and defined variables.
//MyCode.sqf params ["_parameterOne", "_parameterTwo"];
//Inline Function
myInlineFunction ={
params ["_parameterOne", "_parameterTwo"];
};
Parameters passed to functions are passed before the function, rather than after (such as the mathematical or c-like syntax f(x)).
//Array variable as parameter _myTempParams = [_parameterOne, _parameterTwo]; _myTempVariableTwo = _myTempParams call myInlineFunction;
//Array as parameter _myTempVariable = [_parameterOne,_parameterTwo] call myInlineFunction;
Return Values
The value of the last executed statement in a function is returned to the calling instance.
my_fnc = {
if (_this > 0) exitWith {
_this + 1
};
_this - 1
};
hint str (5 call my_fnc); //6
hint str (-5 call my_fnc); //-6
In the first example "_this + 1" is the last executed statement in my_fnc, in the second example it is "_this - 1". Traditionally the returning statement is written without ";" after it. Have it or don't have it, it is up to you, doesn't make a blind bit of difference:
my_fnc = {
a = 1;
b = 2;
c = a + b;
c //<- fine
};
my_fnc = {
a = 1;
b = 2;
c = a + b;
c; //<- also fine
};
More examples:
//myCode.sqf
private _myName = _this select 0;
private _returnMe = "FAIL";
if (_myName == "Test") then {
_returnMe = "PASS";
};
_returnMe
//myCodeInline
myCodeReturnValue ={
private _myName = _this select 0;
private _returnMe = "FAIL";
if (_myName == "Kaboom") then {
_returnMe = "PASS";
};
_returnMe
};
_myCalledVariable = ["Kaboom"] call myCodeReturnValue; // "PASS"
_myCalledVariableFail = ["Blah"] call myCodeReturnValue; // "FAIL"
//return.sqf STATEMENT 1; STATEMENT 2; RETURN_VALUE
//test.sqf value = call compile preprocessFile "return.sqf"; // value is now RETURN_VALUE call compile preprocessFile "return.sqf"; // valid, but RETURN_VALUE is not saved anywhere
Execution
Executing Instance : script, function or game engine
Functions can be executed from several points in the game:
- Other scripts
- Other functions
- Scripting lines in the Mission Editor
- Event Handlers in addon config files
Functions are first loaded as String from a file via preprocessFile or loadFile. They are then executed via the call or spawn command. Since Armed Assault the loaded String needs to be compiled in order to convert it to Code, which is required for call or spawn.
Call
Example (Operation Flashpoint):
myFunction1 = loadFile "myFunction1.sqf"; myFunction2 = preprocessFile "myFunction2.sqf"; call myFunction1; [1, 2] call myFunction2;
Example (Armed Assault):
myFunction1 = compile loadFile "myFunction1.sqf"; myFunction2 = compile preprocessFile "myFunction2.sqf"; _result1 = call myFunction1; _result2 = [1, 2] call myFunction2;
Functions executed using call are run within the executing instance, which waits for the result of the function. Unlike scripts, functions halt all other game engine processes until the function has completed its instructions. This means functions run faster than scripts, and the result of functions is immediate and unambiguous. It can also mean that if a function takes too long to run it will have an adverse effect on game play - large functions or CPU intensive functions can cause the game to seize up until it completes. When creating a functions you want the function to be short and sweet to achieve the best results.
Note: You can still use the special variables and commands of scripts in functions (Armed Assault only)!
Spawn
Functions may also be executed using spawn, but then the function result is not accessible, making it behave more like a procedure. Spawned functions will run asynchronously or alongside the executing instance. This helps prevent large CPU intensive functions from seizing up the game.
Example (Armed Assault):
myFunction1 = compile loadFile "myFunction1.sqf"; myFunction2 = compile preprocessFile "myFunction2.sqf"; _param spawn myFunction1; [1, 2] spawn myFunction2;
Examples
Example 1: max.sqf
In this example the function returns maximum of first and second argument.
max.sqf
//"Return maximum of first and second argument"; params ["_a", "_b"]; [_b, _a] select (_a > _b)
alternative max.sqf (big boys code :))
(_this select 0) max (_this select 1)
executing script:
fMax = compile preprocessFile "max.sqf"; maxValue = [3,5] call fMax; //maxValue is now 5
Example 2: infantrySafe.sqf
In this example the function returns no value and switches all units to safe mode.
//"Switch all infantry units to safe mode";
{
if (vehicle _x == _x) then {
_x setBehaviour "safe"
}
} forEach _this
Example 3: Inline Function
An inline-function can be created in any script:
FNC_sayhello = {hint format ["hello %1", _this]};
This function can then be called (in other scripts, functions, unit's init lines, trigger activation fields, etc.) via:
name player call FNC_sayhello
In case the function doesn't require any arguments you can just call the function.
call FNC_helloall