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Special folders and script compilation order

Unity reserves some project folder names to indicate that the contents have a special purpose. Some of these folders have an effect on the order of script compilation. These folder names are:

  • Assets
  • Editor
  • Editor default resources
  • Gizmos
  • Plugins
  • Resources
  • Standard Assets
  • StreamingAssets

See Special folder names for information on what these folders are used for.

There are four separate phases of script compilation. The phase where a script is compiled is determined by its parent folder.

This is significant in cases where a script must refer to classes defined in other scriptsA piece of code that allows you to create your own Components, trigger game events, modify Component properties over time and respond to user input in any way you like. More info
See in Glossary
. The basic rule is that anything that is compiled in a phase after the current one cannot be referenced. Anything that is compiled in the current phase or an earlier phase is fully available.

Another situation for this occurs when a script written in one language must refer to a class defined in another language (for example, a UnityScript file that declares variables of a class defined in a C# script). The rule here is that the class being referenced must have been compiled in an earlier phase.

The phases of compilation are as follows:

  • Phase 1: Runtime scripts in folders called Standard AssetsA collection of useful assets supplied with Unity. Unity ships with multiple Standard Asset such as 2D, Cameras, Characters, CrossPlatformInput, Effects, Environment, ParticleSystems, Prototyping, Utility, and Vehicles. More info
    See in Glossary
    , Pro Standard Assets and PluginsA set of code created outside of Unity that creates functionality in Unity. There are two kinds of plugins you can use in Unity: Managed plugins (managed .NET assemblies created with tools like Visual Studio) and Native plugins (platform-specific native code libraries). More info
    See in Glossary
    .
  • Phase 2: Editor scripts in folders called Editor that are anywhere inside top-level folders called Standard Assets, Pro Standard Assets and Plugins.
  • Phase 3: All other scripts that are not inside a folder called Editor.
  • Phase 4: All remaining scripts (those that are inside a folder called Editor).

A common example of the significance of this order occurs when a UnityScript file needs to reference a class defined in a C# file. To achieve this, you need to place the C# file inside a Plugins folder, and the UnityScript file in a non-special folder. If you don’t do this, an error is thrown saying that the C# class cannot be found.

Note: Standard Assets work only in the AssetsAny media or data that can be used in your game or project. An asset may come from a file created outside of Unity, such as a 3D model, an audio file or an image. You can also create some asset types in Unity, such as an Animator Controller, an Audio Mixer or a Render Texture. More info
See in Glossary
root folder.

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Platform dependent compilation
Script compilation and assembly definition files