Question

I know C# code can be compiled at runtime using C#. However I’m very very shaky at it since I just read about it a few minutes ago. I learn a lot better by examples. So tell me. If I want to compile something like:

// MapScript.CS
String[] LevelMap = {
"WWWWWWWWWWWWWWWWWWW",
"WGGGGGGGGGGGGGGGGGW",
"WGGGGGGGGGGGGGGGGGW",
"WWWWWWWWWWWWWWWWWWW" };

and use this array in my code, how would I go about it?

In pseudocode I want to do something like this:

Open("MapScript.CS");
String[] levelMap = CompileArray("levelMap");
// use the array

Answer 1

LINQ Expression trees are probably the friendliest way of doing this: Perhaps something like:

• http://msdn.microsoft.com/en-us/library/system.linq.expressions.newarrayexpression.aspx
• http://msdn.microsoft.com/en-us/library/bb357903.aspx

You can also generate the IL using OpCodes (OpCodes.Newarr). Easy if you are comfortable with stack-based programming (otherwise, can be challenging).

Lastly, you can use the CodeDom (which your pseudocode resembles), but–while the most powerful tool–it is less ideal for quick dynamic methods. It requires file system permissions and manual reference resolution since you are working closely with the compiler.

Sample from MSDN

var ca1 = new CodeArrayCreateExpression("System.Int32", 10);                        
var cv1 = new CodeVariableDeclarationStatement("System.Int32[]", "x", ca1);

Source – Creating Arrays with the Code DOM

If you want a straight up raw compile of a string, you can omit the object-oriented treatment of the statements and instead just build a big string. Something like:

var csc = new CSharpCodeProvider( new Dictionary<string, string>() { { "CompilerVersion", "v4.0" } } );
var cp = new CompilerParameters() {
    GenerateExecutable = false,
    OutputAssembly = outputAssemblyName,
    GenerateInMemory = true
};

cp.ReferencedAssemblies.Add( "mscorlib.dll" );
cp.ReferencedAssemblies.Add( "System.dll" );
cp.ReferencedAssemblies.Add( "System.Core.dll" );

StringBuilder sb = new StringBuilder();

// The string can contain any valid c# code, but remember to resolve your references

sb.Append( "namespace Foo{" );
sb.Append( "using System;" );
sb.Append( "public static class MyClass{");

// your specific scenario
sb.Append( @"public static readonly string[] LevelMap = {
    ""WWWWWWWWWWWWWWWWWWW"",
    ""WGGGGGGGGGGGGGGGGGW"",
    ""WGGGGGGGGGGGGGGGGGW"",
    ""WWWWWWWWWWWWWWWWWWW"" };" );

sb.Append( "}}" );

// "results" will usually contain very detailed error messages
var results = csc.CompileAssemblyFromSource( cp, sb.ToString() );