Question

the C# call

Math.Pow(2,3);

in ILDASM:

ldc.r8   2.
ldc.r8   3.
call     float64[mscorlib]System.Math::Pow(float64, float64)

Can someone please tell me how to emit that call statement via an ILGenerator ? Thanks.

Answer 1

Here’s an example of building a dynamic method that will call the static Math.Pow(double, double) method:

using System;
using System.Linq;
using System.Reflection.Emit;

class Program
{
    static void Main()
    {
        // define the signature of the dynamic method
        var powIt = new DynamicMethod(
            "PowIt",
            typeof(double),
            new Type[] { typeof(double), typeof(double) },
            typeof(Program).Module
        );

        // get a MethodInfo pointer to the Math.Pow(double, double) static
        // method that we are willing to use in our dynamic method
        var pow = typeof(Math).GetMethod("Pow", new[] { typeof(double), typeof(double) });

        var il = powIt.GetILGenerator();
        // Push the first argument onto the evaluation stack
        il.Emit(OpCodes.Ldarg_0);
        // Push the second argument onto the evaluation stack
        il.Emit(OpCodes.Ldarg_1);
        // Invoke the Math.Pow static method that we obtained a MethodInfo earlier
        // by passing the two arguments that are on the evaluation stack
        il.Emit(OpCodes.Call, pow);

        // Return from the method pushing a return value from the callee's evaluation stack onto the caller's evaluation stack
        il.Emit(OpCodes.Ret);

        // build a delegate from the dynamic method
        var func = (Func<double, double, double>)powIt.CreateDelegate(typeof(Func<double, double, double>));

        // Now invoke the delegate
        Console.WriteLine(func(2, 3));
    }
}