isNil: Difference between revisions

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|gr1= Variables
|gr1= Variables


|descr= Tests whether the variable given by its name is [[nil]] or undefined, 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 | Informative | {{GVI|ofp|1.00}} This command doesn't exist in {{ofp}} but can be emulated (see '''[[#Examples|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


|p1= variableName: [[String]] - name of a [[missionNamespace]] variable (e.g "someVar") or a local variable (e.g "_someVar")
|p1= variableName: '''[[String]]''' - [[missionNamespace]]'s or local [[Variables|variable]]'s [[Identifier|identifier]] (e.g "globalVariable", "_localVariable")


|r1= [[Boolean]] - [[true]] if variable is [[nil]]
|r1= [[Boolean]] - [[true]] if variable is [[nil]] or undefined


|s2= [[isNil]] code
|s2= [[isNil]] code


|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 [[canSuspend|to suspend]] while expression is evaluated, even if the parent scope allows it (see '''[[#Examples|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 something other than [[Nothing]]
|r2= [[Boolean]] - [[true]] if ''code'' returns [[Nothing]], [[false]] otherwise


|x1= <code>[[if]] ([[isNil]] "pokus") [[then]] { pokus = 0; };</code>
|s3= namespace [[isNil]] variableName
|s3since= arma3 2.18
|p41= namespace: [[Namespace]], [[Object]], [[Group]] or [[HashMap]]
|p42= variableName: [[String]]  
|r3= [[Boolean]] - [[true]] if variable is [[nil]] or undefined


|x2= <code>[[isNil]] { [[player]] [[getVariable]] "someVar" };</code>
|x1= <sqf>
if (isNil "TAG_globalVariable") then { TAG_globalVariable = 0 };
if (isNil "_localVariable") then { hint "_localVariable is nil" };
</sqf>


|x3= <code>_myArray = [0, 1];
|x2= <sqf>isNil { player getVariable "someVar" };</sqf>
[[isNil]] { _myArray [[select]] 0 }; {{cc|returns [[false]]}}
[[isNil]] { _myArray [[select]] 1 }; {{cc|returns [[false]]}}
[[isNil]] { _myArray [[select]] 2 }; {{cc|returns [[true]]}}
[[isNil]] { _myArray [[select]] 3 }; {{cc|throws a script error. only length+1 select is allowed}}
</code>


|x4= You can do this trick to force execute something in [[Scheduler|Unscheduled Environment]].<code>[[spawn]] {
|x3= <sqf>
[[systemChat]] [[str]] [[canSuspend]]; {{cc|chat shows [[true]]}}
_myArray = [0, 1];
[[isNil]] {[[hint]] [[str]] [[canSuspend]]}; {{cc|hint shows [[false]]}}
isNil { _myArray select 0 }; // returns false
};</code>
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
</sqf>


|x5= {{ofp}} workaround:<br>SQS syntax:
|x4= This trick forces executing something in [[Scheduler|Unscheduled Environment]]:
<code>_nil = [[format]] ["%1", _undefinedVariable]
<sqf>
? ([[format]] ["%1", foo] == _nil) : foo = "value"</code>
0 spawn {
SQF syntax:
systemChat str canSuspend; // chat shows true
<code>_nil = [[format]] ["%1", _undefinedVariable];
isNil { hint str canSuspend }; // hint shows false
[[if]] ([[format]] ["%1", foo] == _nil) [[then]] { foo = "value"; };</code>
};
</sqf>


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

Latest revision as of 15:03, 8 February 2024

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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 1

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 or undefined

Syntax 2

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

Syntax 3

Syntax:
namespace isNil variableName
Parameters:
namespace: Namespace, Object, Group or HashMap
variableName: String
Return Value:
Boolean - true if variable is nil or undefined

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=352350"