Question

I know how to create a dynamic method by injecting IL for say a * 2;

However I want to be it like a * b where b is consntant.

Consider this.

int b = SomeClassInstance.Multiplier;

Func<int,int> MultA = CreateDynMethod(b);

for(int i = 0; i < 1000; i++)
{
    int a = GetValueSomewhere();
    int result = MultA(a);
    Console.WriteLine(result);
}

See.. b is the same for all 1000 iteration. However I dont know what it is going to be. 0 1 2 or whatever.

My question is how can I embed the b value in IL as a constant.

This is very important distinction – I dont want to calculate var a * var b. I want (if for example b == 2 in run-time) to create IL which does a * 2.

I have reason to do so. If you please answer the question as it written. Thank you.

EDIT. Here is what I could write with your help. Please tell what do you think

    static Func<int, int> IL_EmbedConst(int b)
    {
        var method = new DynamicMethod("EmbedConst", typeof(int), new[] { typeof(int) } );

        var il = method.GetILGenerator();

        il.Emit(OpCodes.Ldarg_0);
        il.Emit(OpCodes.Ldc_I4, b);
        il.Emit(OpCodes.Mul);
        il.Emit(OpCodes.Ret);

        return (Func<int, int>)method.CreateDelegate(typeof(Func<int, int>));
    }

Answer 1

You want the ldc.i4 opcode.

That will load an int onto the stack, which can then be followed by a mul.

You could use it like this:

ilGen.Emit(OpCodes.Ldc_I4, b);

By the way, you don’t really need to build methods from IL here. This method would work as well:

Func<int, int> CreateDynMethod(int b)
{
    return a => a * b;
}