Platform Accessors - How to change the way MoonSharp interacts with the OS

This tutorial will be brief and assumes that you’ve followed the tutorial on script loaders to the end.

If you didn’t, please go back and learn everything about script loaders first.

Platform accessors are very similar to script loaders although they serve a different purpose. Platform accessors are meant to provide access to OS APIs to suit the standard library or other accessory parts of MoonSharp. In particular, the io, file and os modules heavily depend on platform accessors, but other methods go through the platform accessor, like print, debug.debug and others.

A quick tour of predefined platform accessors

Depending on the platforms you run to you have these choices of platform accessors :

• StandardPlatformAccessor : implements all the needed methods, going to files, environment variables, etc.
• LimitedPlatformAccessor : very limited support. Disables the io, file and parts of the os modules.

The default script loader used by MoonSharp if no redefinition happens is LimitedPlatformAccessor for the portable class library build and StandardPlatformAccessor for the other builds.

Changing the platform accessor

Changing the platform accessor impacts all scripts, both created or not. Because of this, changing the platform accessor should NEVER be done once a script has been created. For the sake of this tutorial we’ll do it anyway, but please don’t do it.

static void ChangePlatform()
{
	// This prints "function"
	Console.WriteLine(Script.RunString("return type(os.exit);").ToPrintString());

	// Save the old platform
	var oldplatform = Script.GlobalOptions.Platform;

	// Changing platform after a script has been created is not recommended.. do not do it.
	// We are doing it for the purpose of the walkthrough..
	Script.GlobalOptions.Platform = new LimitedPlatformAccessor();

	// This time, this prints "nil"
	Console.WriteLine(Script.RunString("return type(os.exit);").ToPrintString());

	// Restore the old platform
	Script.GlobalOptions.Platform = oldplatform;
}

Implementing your own platform accessor

You can implement your own platform accessor to define how some functions behave.

As for script loaders you have two main options: extend PlatformAccessorBase (recommended) or implement IPlatformAccessor.

To take decisions about the real platform you are running on, see the PlatformAutoDetector which performs a lot of runtime checks to try to understand which platform it’s running on.

Customizing some aspects of the platform accessor

There are a few aspects of a platform accessor which are often going to be customized. To avoid having to implement a custom platform accessor everytime you want to redefine how print behaves, some of these are exposed in script options. See the next chapter about script options.