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using_kotlin.md: companion object usage in extensions

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Yann Cébron 2023-09-06 16:59:45 +02:00
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8
topics/basics/plugin_structure/plugin_extensions.md
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@ -78,9 +78,11 @@ Please note the following important points:
- Extension implementations should be stateless. Use explicit [](plugin_services.md) for managing (runtime) data.
- Avoid any initialization in constructor, see also notes for [Services](plugin_services.md#constructor).
- Kotlin: Do not use `object` but `class` for implementation ([more details](using_kotlin.md#caution)).
- Kotlin: Do not use `companion object` to avoid excessive classloading/initialization when the extension class is loaded.
Use top-level declarations or objects instead.
When using Kotlin:
- Do not use `object` but `class` for implementation. [More details](using_kotlin.md#object-vs-class)
- Do not use `companion object` to avoid excessive classloading/initialization when the extension class is loaded.
Use top-level declarations or objects instead. [More details](using_kotlin.md#companion-object-extensions)
</procedure>

14
topics/tutorials/using_kotlin.md
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@ -161,7 +161,10 @@ You can find the current state of the issue in [KT-57757](https://youtrack.jetbr
Please see [Third-Party Software and Licenses](https://www.jetbrains.com/legal/third-party-software/).
## Caution
## Plugin Implementation Notes
### Do not use "object" but "class"
{id="object-vs-class"}
Plugins *may* use [Kotlin classes](https://kotlinlang.org/docs/classes.html) (`class` keyword) to implement declarations in the [plugin configuration file](plugin_configuration_file.md).
When registering an extension, the platform uses a dependency injection framework to instantiate these classes at runtime.
@ -172,6 +175,15 @@ Problems are highlighted via these inspections (2023.2):
- <control>Plugin DevKit | Code | Kotlin object registered as extension</control> for Kotlin code
- <control>Plugin DevKit | Plugin descriptor | Extension class is a Kotlin object</control> for <path>plugin.xml</path>
### Do not use "companion object" in extensions
{id="companion-object-extensions"}
Kotlin `companion object` is always created once you try to load its containing class, and [extension point implementations](plugin_extensions.md) are supposed to be cheap to create.
To avoid unnecessary classloading (and thus slowdown in IDE startup), `companion object` in extensions must only contain simple constants or [logger](ide_infrastructure.md#logging).
Anything else must be a top-level declaration or stored in an `object`.
Use inspection <control>Plugin DevKit | Code | Companion object in extensions</control> to highlight such problems (2023.3).
## Kotlin Code FAQ
[How to shorten references](https://intellij-support.jetbrains.com/hc/en-us/community/posts/360010025120-Add-new-parameter-into-kotlin-data-class-from-IDEA-plugin?page=1#community_comment_360002950760)