Difference between revisions of "NULL KEY"
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return (in == NULL_KEY); | return (in == NULL_KEY); | ||
}//returns 2 if it's a valid key, 1 if it's NULL_KEY</lsl> | }//returns 2 if it's a valid key, 1 if it's NULL_KEY</lsl> | ||
<lsl>// NULL_KEY itself is evaluated as FALSE only when it is casted as a key. | |||
default { | |||
state_entry() { | |||
if (NULL_KEY) { llOwnerSay("NULL_KEY is TRUE"); }// Correct. | |||
else { llOwnerSay("NULL_KEY is FALSE"); }// Never. | |||
if ((key) NULL_KEY) { llOwnerSay("Casted NULL_KEY is TRUE"); }// Never. | |||
else { llOwnerSay("Casted NULL_KEY is FALSE"); }// Correct. | |||
} | |||
}</lsl> | |||
|notes=In most situations NULL_KEY isn't needed; an empty string ("") will suffice. To take advantage of this certain practices have to be avoided. In many applications keys are checked against NULL_KEY to determine if they are valid; this is bad practice. | |notes=In most situations NULL_KEY isn't needed; an empty string ("") will suffice. To take advantage of this certain practices have to be avoided. In many applications keys are checked against NULL_KEY to determine if they are valid; this is bad practice. | ||
Revision as of 05:07, 11 June 2009
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Description
Constant: string NULL_KEY = "00000000-0000-0000-0000-000000000000";The string constant NULL_KEY has the value "00000000-0000-0000-0000-000000000000"
While technically a string constant, it is only useful as a key.
Despite fitting the syntax criteria to be a valid key, when fed to a Conditional as a key it executes as FALSE.
Caveats
Related Articles
Functions
| • | llAvatarOnSitTarget | |||
| • | llDetectedKey | |||
| • | llGetNotecardLine | |||
| • | llGetLandOwnerAt | |||
| • | llGetPermissionsKey | |||
| • | llGetTexture | |||
| • | llListen |
Events
| • | attach |
Examples
<lsl>integer isKey(key in) {
if(in) return 2; return (in == NULL_KEY);
}//returns 2 if it's a valid key, 1 if it's NULL_KEY</lsl> <lsl>// NULL_KEY itself is evaluated as FALSE only when it is casted as a key. default {
state_entry() {
if (NULL_KEY) { llOwnerSay("NULL_KEY is TRUE"); }// Correct.
else { llOwnerSay("NULL_KEY is FALSE"); }// Never.
if ((key) NULL_KEY) { llOwnerSay("Casted NULL_KEY is TRUE"); }// Never.
else { llOwnerSay("Casted NULL_KEY is FALSE"); }// Correct.
}
}</lsl>
Notes
Like any LSO string constants longer then 3 characters and used in multiple places in the code, they should be stored in a global variable. The result will be a considerable memory savings. This does not apply to scripts compiled with Mono. See LSL Constants vs Globals for more information about this and examples.
In most situations NULL_KEY isn't needed; an empty string ("") will suffice. To take advantage of this certain practices have to be avoided. In many applications keys are checked against NULL_KEY to determine if they are valid; this is bad practice.
LSL makes it easy to check if a key is valid. Simply use the key as the parameter for a conditional.
That is, instead of if(uuid != NULL_KEY), use if(uuid). if(uuid) will only return TRUE if it is a valid key that is also not a null key.