Version: 2018.1 (switch to 2018.2b or 2017.4)
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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 scripts. 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 Assets, Pro Standard Assets and Plugins.
  • 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 Assets root folder.

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Platform dependent compilation
Script compilation and assembly definition files