isNil: Difference between revisions

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m (Text replacement - "{{HashLink" to "{{Link")
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|descr= Tests whether a variable is [[nil]] or undefined from its [[Identifier|identifier]], or whether the given expression evaluates to [[nil]] or [[Nothing]].
|descr= Tests whether a variable is [[nil]] or undefined from its [[Identifier|identifier]], or whether the given expression evaluates to [[nil]] or [[Nothing]].
{{Feature | arma0 | This command does not exist in {{ofp}}/{{arma0}} but can be emulated (see {{HashLink|#Example 5}}).}}
{{Feature|arma0|This command does not exist in {{ofp}}/{{arma0}} but can be emulated (see {{Link|#Example 5}}).}}


|s1= [[isNil]] variableName
|s1= [[isNil]] variableName
Line 30: Line 30:


|p21= code: [[Code]] - code to evaluate:
|p21= code: [[Code]] - code to evaluate:
* the code '''will''' be executed; {{ic|[[isNil]] { [[player]] [[setDamage]] 1 };}} ''will'' kill the player
* the code '''will''' be executed; <sqf inline>isNil { player setDamage 1 };</sqf> ''will'' kill the player
* the code will not be allowed to [[canSuspend|suspend]] while expression is evaluated, even if the parent scope allows it (see {{HashLink|#Example 4}}).
* the code will not be allowed to [[canSuspend|suspend]] while expression is evaluated, even if the parent scope allows it (see {{Link|#Example 4}}).


|r2= [[Boolean]] - [[true]] if ''code'' returns [[Nothing]], [[false]] otherwise
|r2= [[Boolean]] - [[true]] if ''code'' returns [[Nothing]], [[false]] otherwise


|x1= <code>[[if]] ([[isNil]] "TAG_globalVariable") [[then]] { TAG_globalVariable = 0 };
|x1= <sqf>
[[if]] ([[isNil]] "_localVariable") [[then]] { [[hint]] "_localVariable is nil" };</code>
if (isNil "TAG_globalVariable") then { TAG_globalVariable = 0 };
if (isNil "_localVariable") then { hint "_localVariable is nil" };
</sqf>


|x2= <code>isNil { player getVariable "someVar" };</code>
|x2= <sqf>isNil { player getVariable "someVar" };</sqf>


|x3= <code>_myArray = [0, 1];
|x3= <sqf>
[[isNil]] { _myArray [[select]] 0 }; // returns [[false]]
_myArray = [0, 1];
[[isNil]] { _myArray [[select]] 1 }; // returns [[false]]
isNil { _myArray select 0 }; // returns false
[[isNil]] { _myArray [[select]] 2 }; // returns [[true]]
isNil { _myArray select 1 }; // returns false
[[isNil]] { _myArray [[select]] 3 }; // throws a script error. only length+1 select is allowed
isNil { _myArray select 2 }; // returns true
</code>
isNil { _myArray select 3 }; // throws a script error. only length+1 select is allowed
</sqf>


|x4= This trick forces executing something in [[Scheduler|Unscheduled Environment]]:
|x4= This trick forces executing something in [[Scheduler|Unscheduled Environment]]:
<code>0 [[spawn]] {
<sqf>
[[systemChat]] [[str]] [[canSuspend]]; // chat shows [[true]]
0 spawn {
[[isNil]] { [[hint]] [[str]] [[canSuspend]] }; // hint shows [[false]]
systemChat str canSuspend; // chat shows true
};</code>
isNil { hint str canSuspend }; // hint shows false
};
</sqf>


|x5= {{ofp}} [[String]] comparison workaround:
|x5= {{ofp}} [[String]] comparison workaround<br>
<code>{{codecomment|; [[SQS Syntax]]}}
[[SQS Syntax]]:
_nil = [[format]] ["%1", _undefinedVariable]
<sqs>
? ([[format]] ["%1", variableToTest] == _nil) : [[hint]] "variableToTest is nil"</code>
_nil = format ["%1", _undefinedVariable]
<code>// [[SQF Syntax]]
? (format ["%1", variableToTest] == _nil) : hint "variableToTest is nil"
_nil = [[format]] ["%1", _undefinedVariable];
</sqs>
[[if]] ([[format]] ["%1", variableToTest] == _nil) [[then]] { [[hint]] "variableToTest is nil" };</code>
 
[[SQF Syntax]]:
<sqf>
_nil = format ["%1", _undefinedVariable];
if (format ["%1", variableToTest] == _nil) then { hint "variableToTest is nil" };
</sqf>


|seealso= [[nil]] [[Variables]] [[Scheduler]]
|seealso= [[nil]] [[Variables]] [[Scheduler]]
}}
}}

Revision as of 18:43, 4 January 2023

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Hover & click on the images for description

Description

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

Syntax

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

Alternative Syntax

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

Examples

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" };

Additional Information

See also:
nil Variables Scheduler

Notes

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
Retrieved from "https://community.bistudio.com/wiki?title=isNil&oldid=336860"