isNil: Difference between revisions

Revision as of 14:01, 12 May 2022

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Description:: Tests whether a variable is nil or undefined from its identifier, or whether the given expression evaluates to nil or Nothing.
This command does not exist in Operation Flashpoint/Arma: Cold War Assault but can be emulated (see Example 5).
Groups:: Variables

Syntax:: isNil variableName
Parameters:: variableName: String - missionNamespace's or local variable's identifier (e.g "globalVariable", "_localVariable")
Return Value:: Boolean - true if variable is nil

Syntax:

isNil code

Parameters:

code: Code - code to evaluate:

the code will be executed; isNil { player setDamage 1 }; will kill the player
the code will not be allowed to suspend while expression is evaluated, even if the parent scope allows it (see Example 4).

Return Value:

Boolean - true if code returns Nothing, false otherwise

Example 1:: if (isNil "TAG_globalVariable") then { TAG_globalVariable = 0 }; if (isNil "_localVariable") then { hint "_localVariable is nil" };
Example 2:: isNil { player getVariable "someVar" };
Example 3:: _myArray = [0, 1]; isNil { _myArray select 0 }; // returns false isNil { _myArray select 1 }; // returns false isNil { _myArray select 2 }; // returns true isNil { _myArray select 3 }; // throws a script error. only length+1 select is allowed
Example 4:: This trick forces executing something in Unscheduled Environment: 0 spawn { systemChat str canSuspend; // chat shows true isNil { hint str canSuspend }; // hint shows false };
Example 5:: Operation Flashpoint String comparison workaround: ; SQS Syntax _nil = format ["%1", _undefinedVariable] ? (format ["%1", variableToTest] == _nil) : hint "variableToTest is nil" // SQF Syntax _nil = format ["%1", _undefinedVariable]; if (format ["%1", variableToTest] == _nil) then { hint "variableToTest is nil" };

: Report bugs on the Feedback Tracker and/or discuss them on the Arma Discord or on the Forums.
Only post proven facts here! Add Note

@@ Line 41: / Line 41: @@
 |x3= <code>_myArray = [0, 1];
-isNil { _myArray [[select]] 0 }; // returns [[false]]
+isNil { _myArray select 0 }; // returns [[false]]
 [[isNil]] { _myArray [[select]] 1 }; // returns [[false]]
 [[isNil]] { _myArray [[select]] 2 }; // returns [[true]]
@@ Line 48: / Line 48: @@
 |x4= This trick forces executing something in [[Scheduler|Unscheduled Environment]]:
 <code>0 spawn {
-	systemChat [[str]] [[canSuspend]];		// chat shows [[true]]
+	systemChat str [[canSuspend]];		// chat shows [[true]]
 	[[isNil]] { [[hint]] [[str]] [[canSuspend]] };	// hint shows [[false]]
 };</code>