Emitting IL chiamare una funzione matematica

Question

il C# chiamata

Math.Pow(2,3); 

in ILDASM:

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

qualcuno può dirmi come emettere questa affermazione chiamata tramite un ILGenerator? Grazie.

Answer 1

Ecco un esempio di costruzione di un metodo dinamico che chiamerà il metodo statico Math.Pow(double, double):

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)); 
    } 
}