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Emitting Methods
You can specify a return type and parameter types when calling DefineMethod, in the
same manner as when instantiating a DynamicMethod; e.g., the following method:
public static double SquareRoot (double value)
{
return Math.Sqrt (value);
}
can be generated like this:
MethodBuilder mb = tb.DefineMethod ("SquareRoot",
MethodAttributes.Static | MethodAttributes.Public,
CallingConventions.Standard,
typeof (double), // Return type
new[] { typeof (double) } ); // Parameter types
mb.DefineParameter (1, ParameterAttributes.None, "value"); // Assign name
ILGenerator gen = mb.GetILGenerator();
gen.Emit (OpCodes.Ldarg_0); // Load 1st arg
gen.Emit (OpCodes.Call, typeof(Math).GetMethod ("Sqrt"));
gen.Emit (OpCodes.Ret);
Type realType = tb.CreateType();
double x = (double) tb.GetMethod ("SquareRoot").Invoke (null,
new object[] { 10.0 });
Console.WriteLine (x); // 3.16227766016838
Calling DefineParameter is optional and is typically done to assign the parameter a
name. The number 1 refers to the first parameter (0 refers to the return value). If you
call DefineParameter, the parameter is implicitly named __p1, __p2, and so on. Assigning
names makes sense if you will write the assembly to disk; it makes your
methods friendly to consumers.
DefineParameter returns a ParameterBuilder object upon which
you can call SetCustomAttribute to attach attributes (see “Attaching
Attributes” on page 722, later in this chapter).
To emit pass-by-reference parameters, such as in the following C# method:
public static void SquareRoot (ref double value)
{
value = Math.Sqrt (value);
}
call MakeByRefType on the parameter type(s):
MethodBuilder mb = tb.DefineMethod ("SquareRoot",
MethodAttributes.Static | MethodAttributes.Public,
CallingConventions.Standard,
null,
new Type[] { typeof (double).MakeByRefType() } );
718 | Chapter 18: Reflection and Metadata