{{tag>zxt:extension}}

====== 00000000:0001 - #IFEXT ======

===== Information =====

  * **ID:** 00000000:0001

===== Flags =====

^ Flag ^ Set? (MUST/MAY/...) ^ Description ^
| parsing_must | MUST NOT | |
| reading_must | MUST NOT | |
| writing_must | MUST NOT | |
| playing_should | MAY | If any #IFEXT calls are used in Objects with the described caveat for optional support. |
| playing_must | MAY | If any #IFEXT calls are used in Objects. |
| editing_should | MUST NOT | |

===== Field data =====

None.

===== Description =====

This extension adds an OOP command which faciliates run-time detection of extensions on both ZZT 3.2 and ZXT-compatible implementations. The command is ''#IFEXT owner_id selector_id ...'', where owner_id and selector_id are specified as 32-bit and 16-bit hexadecimal numbers, respectively. If the extension with a given owner_id and selector_id is currently active within the execution context, the rest of the line is treated as a command.

Keep in mind that to support ''#IFEXT'' as an optional extension, an '':IFEXT'' label SHOULD be provided to handle the situation in which this extension is not present.

===== Example usage =====

==== Simple scenario ====

<code>
#ifext 00000000 0001 found
:found
Extensions found!
#end
:ifext
Extensions not found.
#end
</code>

==== Two touch codepaths ====

<code>
@Interactive
#ifext 00000000 0001 zap touch
:ifext
#end
:touch
I found nothing...
#end
:touch
I found IFEXT support!
#end
</code>

==== Two touch codepaths (#BIND workaround) ====

If the code above is bound, '':TOUCH'' might end up being zapped multiple times. This code takes care of that:

<code>
@Interactive
#send init
#end
:init
#zap init
#ifext 00000000 0001 zap touch
:ifext
#end
:touch
I found nothing...
#end
:touch
I found IFEXT support!
#end
</code>

An alternative, more advanced technique is pre-setting the instruction pointer in an external editor.

===== Implementations =====