Interactive C# Code Completion

by Miguel de Icaza

Last month I introduced code completion in Mono's Interactive C# shell. You can use the TAB key to auto-complete at the current cursor position. Pressing the TAB key twice will list all possible completions.

This should make the csharp more pleasurable to use and for bash junkies like me a more natural fit.

This is particularly useful to explore an API like Gtk#:

	csharp> LoadPackage ("gtk-sharp-2.0");
	csharp> using Gtk;
	csharp> Application.Init ();
	csharp> var w = new Window ("Hello");
	csharp> w.SetF[tab]
	SetFlag SetFocus SetFrameDimensions
	csharp> w.SetFo[tab]
	csharp> w.SetFocus ();

This comes in quite handy for completing namespaces, types and valid methods. It works with the C# 3.0 initializer syntax as well, that one is useful in Silverlight for those of us that can not stand to type XAML instead of C#:

	csharp> new TextBlock () { Bac[tab]

Does the nice:

	csharp> new TextBlock () { Background

Bonus points: another tab at that point inserts the equal sign to assign the value.

This was done by extending the Mono.CSharp.Evaluator API to provide code completion.

The API is fairly simple:

public static string [] GetCompletions (string input, out string prefix)

This will provide possible completions (methods, properties, fields) that are valid at that point in the string.

A discussion that details the implementation of how the compiler supports code completion is in the mailing list and our compiler documentation has been updated to include a tutorial on expanding code completion.

The next step is to implement this for the interactive GUI shell.

Posted on 28 Apr 2009