ILGenerator

ILGeneratorRequest requests an ILGenerator from ConstructorBuilder or MethodBuilder.

// Request to create method builder for "MyFunction"
IRequestFor<MethodBuilder> myFunc = new MethodBuilderRequest("MyFunction", MethodAttributes.Public | MethodAttributes.Virtual, null, typeof(int), typeof(int));
// Request to create il generator
IRequestFor<ILGenerator> il = ILGeneratorRequest.Default;

When all opcode requests have been appended to il request, then il request is added to method request.

// Add il to "MyFunction"
myFunc = myFunc.Append(il);

Emit

Emit is a request to emit an Opcode to ILGenerator. Opcodes are listed on MSDN.

// Load first argument
il = il.Append(new Emit(OpCodes.Ldarg_1));

Extension method IRequestFor<ILGenerator>.Add() and ILGenerator.Add() has shorter notation.

// Load constant 5
il = il.Append(OpCodes.Ldc_I4_5);

Label

LabelRequest is a request to create a label.

// Define labels
IRequestFor<Label> trueLabel = new LabelRequest(), falseLabel = new LabelRequest();

MarkLabelRequest adds Label to il stream.

il = il.Append(new MarkLabelRequest(trueLabel));

LocalBuilder

LocalBuilderRequest is a request to create a local variable.

// Create local variable
IRequestFor<LocalBuilder> local = new LocalBuilderRequest(typeof(int));
// Add to il request
il = il.Append(local);

The local request can be used with OpCodes.Stloc.

// Write '5' to local
il = il.Append(OpCodes.Ldc_I4_5)
       .Append(OpCodes.Stloc, local);

And with OpCodes.Ldloc.

// Read from local
il = il.Append(OpCodes.Ldloc, local);

EmitCast

EmitCast is a request to emit an opcode that casts one type to another. Reference types can be up and down-casted, value types can be boxed and unboxed.

// Load first argument (object)
il = il.Append(OpCodes.Ldarg_1);
// Add request to emit opcode to box int to object
il = il.Append(new EmitCast(typeof(int), typeof(object)));
// Return
il = il.Append(OpCodes.Ret);

Indirect load and store

In this example, we get a pointer to insides of a box object.

// Load first argument (object)
il = il.Append(OpCodes.Ldarg_1);
// Get Unbox -method
MethodInfo unbox = typeof(System.Runtime.CompilerServices.Unsafe).GetMethod("Unbox")!.MakeGenericMethod(typeof(int));
// Load pointer on stack
il = il.Append(OpCodes.Call, unbox);

EmitLdInd is a request to emit an opcode to read a value from pointer into stack.

// Load indirect (read from pointer)
il = il.Append(new EmitLdInd(typeof(int)));

EmitStInd is a request to emit an opcode to write the value on stack to memory pointer.

// Double value
il = il.Append(OpCodes.Dup).Append(OpCodes.Add);
// Store indirect (write to pointer)
il = il.Append(new EmitStInd(typeof(int)));

Full Example

Full example

using System;
using System.Reflection;
using System.Reflection.Emit;
using Avalanche.Emit;
using Avalanche.Service;

public class emit
{
    public static void Run()
    {
        // LabelRequest & MarkLabelRequest
        {
            // Service that handles assembly builder, module builder and type builder
            IService service = Services.Create(Avalanche.Emit.Module.Instance);
            // Request to create type builder
            IRequestFor<TypeBuilder> typeBuilder = new TypeBuilderRequest("MyClassOp1", TypeAttributes.Public | TypeAttributes.Class | TypeAttributes.AutoClass);
            // <00>
            // Request to create method builder for "MyFunction"
            IRequestFor<MethodBuilder> myFunc = new MethodBuilderRequest("MyFunction", MethodAttributes.Public | MethodAttributes.Virtual, null, typeof(int), typeof(int));
            // Request to create il generator
            IRequestFor<ILGenerator> il = ILGeneratorRequest.Default;
            // </00>

            // <03>
            // Define labels
            IRequestFor<Label> trueLabel = new LabelRequest(), falseLabel = new LabelRequest();
            // </03>

            // "return x < 5 ? 0 : 1"
            // <01>
            // Load first argument
            il = il.Append(new Emit(OpCodes.Ldarg_1));
            // </01>

            // <02>
            // Load constant 5
            il = il.Append(OpCodes.Ldc_I4_5);
            // </02>

            il = il.Append(OpCodes.Clt).Append(OpCodes.Brtrue_S, falseLabel);
            // <04>
            il = il.Append(new MarkLabelRequest(trueLabel));
            // </04>
            // true: return 1;
            il = il.Append(OpCodes.Ldc_I4_1).Append(OpCodes.Ret);
            // true: return 1;
            il = il.Append(new MarkLabelRequest(trueLabel)).Append(OpCodes.Ldc_I4_1).Append(OpCodes.Ret);
            // false: return 0;
            il = il.Append(new MarkLabelRequest(falseLabel)).Append(OpCodes.Ldc_I4_0).Append(OpCodes.Ret);

            // <0B>
            // Add il to "MyFunction"
            myFunc = myFunc.Append(il);
            // </0B>
            // Add "MyFunction"
            typeBuilder = typeBuilder.Append(myFunc);

            // Request to build type
            IRequestFor<Type> type = new TypeRequest(typeBuilder);
            // Request to create new instance
            IRequestFor<Object> newRequest = type.NewRequest();

            // Print request
            newRequest.PrintTreeTo(Console.Out);

            // Get instance
            object instance = service.GetRequired<IRequestFor<object>, object>(newRequest);
            // Evaluate: value = 4 < 5 ? 0 : 1;
            int value = (int)instance.GetType().GetMethod("MyFunction", new Type[] { typeof(int) })!.Invoke(instance, new object[] { 4 })!;
            // Print 
            Console.WriteLine(value);
        }

        // LocalBuilder
        {
            // Service that handles assembly builder, module builder and type builder
            IService service = Services.Create(Avalanche.Emit.Module.Instance);
            // Request to create type builder
            IRequestFor<TypeBuilder> typeBuilder = new TypeBuilderRequest("MyClassOp2", TypeAttributes.Public | TypeAttributes.Class | TypeAttributes.AutoClass);
            // Request to create method
            IRequestFor<MethodBuilder> myFunc = new MethodBuilderRequest("MyFunction", MethodAttributes.Public | MethodAttributes.Virtual, null, typeof(int));
            // Request to create il generator
            IRequestFor<ILGenerator> il = ILGeneratorRequest.Default;

            // <05>
            // Create local variable
            IRequestFor<LocalBuilder> local = new LocalBuilderRequest(typeof(int));
            // Add to il request
            il = il.Append(local);
            // </05>

            // <06>
            // Write '5' to local
            il = il.Append(OpCodes.Ldc_I4_5)
                   .Append(OpCodes.Stloc, local);
            // </06>

            // <07>
            // Read from local
            il = il.Append(OpCodes.Ldloc, local);
            // </07>
            // Read from local again
            il = il.Append(OpCodes.Ldloc, local);
            // Sum up
            il = il.Append(OpCodes.Add);
            // Return
            il = il.Append(OpCodes.Ret);

            // Add il to "MyFunction"
            myFunc = myFunc.Append(il);
            // Add "MyFunction"
            typeBuilder = typeBuilder.Append(myFunc);

            // Request to build type
            IRequestFor<Type> type = new TypeRequest(typeBuilder);
            // Request to create new instance
            IRequestFor<Object> newRequest = type.NewRequest();

            // Print request
            newRequest.PrintTreeTo(Console.Out);

            // Get instance
            object instance = service.GetRequired<IRequestFor<object>, object>(newRequest);
            // Call function
            int value = (int)instance.GetType().GetMethod("MyFunction", Type.EmptyTypes)!.Invoke(instance, null)!;
            // Print 
            Console.WriteLine(value);
        }

        // EmitCast
        {
            // Service that handles assembly builder, module builder and type builder
            IService service = Services.Create(Avalanche.Emit.Module.Instance);
            // Request to create type builder
            IRequestFor<TypeBuilder> typeBuilder = new TypeBuilderRequest("MyClassOp3", TypeAttributes.Public | TypeAttributes.Class | TypeAttributes.AutoClass);
            // Request to create method
            IRequestFor<MethodBuilder> myFunc = new MethodBuilderRequest(
                name: "MyFunction",
                methodAttributes: MethodAttributes.Public | MethodAttributes.Virtual,
                attributes: null,
                returnType: typeof(object),
                parameterTypes: typeof(int));
            // Request to create il generator
            IRequestFor<ILGenerator> il = ILGeneratorRequest.Default;

            // <10>
            // Load first argument (object)
            il = il.Append(OpCodes.Ldarg_1);
            // Add request to emit opcode to box int to object
            il = il.Append(new EmitCast(typeof(int), typeof(object)));
            // Return
            il = il.Append(OpCodes.Ret);
            // </10>

            // Add il to "MyFunction"
            myFunc = myFunc.Append(il);
            // Add "MyFunction"
            typeBuilder = typeBuilder.Append(myFunc);

            // Request to build type
            IRequestFor<Type> type = new TypeRequest(typeBuilder);
            // Request to create new instance
            IRequestFor<Object> newRequest = type.NewRequest();

            // Print request
            newRequest.PrintTreeTo(Console.Out);

            // Get instance
            object instance = service.GetRequired<IRequestFor<object>, object>(newRequest);
            // Box
            object box = 9;
            // Call function
            int value = (int)instance.GetType().GetMethod("MyFunction", new Type[] { typeof(int) })!.Invoke(instance, new object[] { box })!;
            // Print 
            Console.WriteLine(value);
        }

        // LdIndEmit & StIndEmit
        {
            // Service that handles assembly builder, module builder and type builder
            IService service = Services.Create(Avalanche.Emit.Module.Instance);
            // Request to create type builder
            IRequestFor<TypeBuilder> typeBuilder = new TypeBuilderRequest("DoublerClass", TypeAttributes.Public | TypeAttributes.Class | TypeAttributes.AutoClass);
            // Request to create method
            IRequestFor<MethodBuilder> myFunc = new MethodBuilderRequest(
                name: "Double",
                methodAttributes: MethodAttributes.Public | MethodAttributes.Virtual,
                attributes: null,
                returnType: null,
                parameterTypes: typeof(object));
            // Request to create il generator
            IRequestFor<ILGenerator> il = ILGeneratorRequest.Default;

            // <20>
            // Load first argument (object)
            il = il.Append(OpCodes.Ldarg_1);
            // Get Unbox -method
            MethodInfo unbox = typeof(System.Runtime.CompilerServices.Unsafe).GetMethod("Unbox")!.MakeGenericMethod(typeof(int));
            // Load pointer on stack
            il = il.Append(OpCodes.Call, unbox);
            // </20>
            // Copy the pointer to stack again, for load and store
            il = il.Append(OpCodes.Dup);

            // <21>
            // Load indirect (read from pointer)
            il = il.Append(new EmitLdInd(typeof(int)));
            // </21>

            // <22>
            // Double value
            il = il.Append(OpCodes.Dup).Append(OpCodes.Add);
            // Store indirect (write to pointer)
            il = il.Append(new EmitStInd(typeof(int)));
            // </22>

            // Return
            il = il.Append(OpCodes.Ret);

            // Add il to "Double"
            myFunc = myFunc.Append(il);
            // Add "Double"
            typeBuilder = typeBuilder.Append(myFunc);

            // Request to build type
            IRequestFor<Type> type = new TypeRequest(typeBuilder);
            // Request to create new instance
            IRequestFor<Object> newRequest = type.NewRequest();

            // Print request
            newRequest.PrintTreeTo(Console.Out);

            // Get instance
            object instance = service.GetRequired<IRequestFor<object>, object>(newRequest);
            // Box
            object box = 4;
            // Call "Double"
            instance.GetType().GetMethod("Double", new Type[] { typeof(object) })!.Invoke(instance, new object[] { box });
            // Print box -> "8"
            Console.WriteLine(box);
        }
    }
}