EmitToolbox

Using System.Reflection.Emit to dynamically create types and methods at runtime is prone to errors and can be quite complex. To effectively emit dynamic IL code, one must have a deep understanding of the Common Intermediate Language (CIL) and the .NET runtime. The EmitToolbox library aims to simplify this process by providing a set of high-level abstractions and utilities.

Framework

Contexts:

• AssemblyBuildingContext - Context for building dynamic assemblies.
• TypeBuildingContext - Context for building dynamic types.
• MethodBuildingContext - Context for building dynamic methods.
• ㇄ ActionMethodBuildingContext - Context for building dynamic methods that does not have a return value.
• ㇄ FuncMethodBuildingContext - Context for building dynamic methods that has a return value.
• FieldBuildingContext - Context for building fields of the dynamic types.
• PropertyBuildingContext - Context for building properties of the dynamic types.

Usage

Basic Usage

using EmitToolbox;

// Define an context for an executable (and cannot be saved) assembly.
var assemblyContext = AssemblyBuildingContext
            .CreateExecutableContextBuilder("SampleDynamicAssembly")
            .Build();
            
// Define a context for a class type within the assembly.
var typeContext = assemblyContext.DefineClass("SampleClass"); 

// Define a field.
var fieldContext = typeContext.Fields.Instance<int>("_value", FieldAttributes.Private);

// Define a method.
var methodContext = typeContext.Functors.Instance("AddAndSet", 
            [ParameterDefinition.Value<int>()], ResultDefinition.Value<int>());
var argumentSymbol = methodContext.Argument<int>(1)
var fieldSymbol = fieldContext.Symbol(methodContext.This);
var resultSymbol = fieldSymbol.Add(argumentSymbol);
fieldSymbol.Assign(resultSymbol);
methodContext.Return(resultSymbol);

// Generate the type.
typeContext.Build();

// Create an instance of the generated type.
var instance = Activator.CreateInstance(typeContext.BuildingType);

var result1 = methodContext.BuildingMethod.Invoke(null, [1])
Console.WriteLine(result1); // Output: 1
var result2 = methodContext.BuildingMethod.Invoke(null, [2])
Console.WriteLine(result2); // Output: 3

Create a symbol for an argument: methodContext.Argument<int>(0).

Create a local variable: methodContext.Variable<int>().

Create a symbol for a literal value: methodContext.Value(123).

Supported literal types:

• Integers: byte, sbyte, short, ushort, int, uint, long, ulong;
• Floating points: float, double, decimal;
• bool, char, string;
• null for reference types.
• Enumeration values.
• Metadata: Type, FieldInfo, PropertyInfo, ConstructorInfo, MethodInfo;

Array Facade

// Use .AsArray() to convert a symbol of an array type to an array facade.
var array = methodContext.Argument<int[]>(0).AsArray();

var elementFromLiteralIndex = array[0]; // Get an element using a literal index.
var elementFromSymbolIndex = array[methodContext.Argument<int>(1)]; // Get an element using a index symbol.

If-Else

Following code can generate a method which is equal to (bool condition) => condition ? 1 : 0:

var methodContext = typeContext.Functors.Static("Test",
    [ParameterDefinition.Value<bool>()], ResultDefinition.Value<int>());
var argument = methodContext.Argument<bool>(0);
methodContext.If(argument,
    () =>
    {
        methodContext.Return(methodContext.Value(1));
    },
    () =>
    {
        methodContext.Return(methodContext.Value(0)); 
    });
methodContext.Return(methodContext.Value(-1));

Loop

For C# code like below:

int method(int arg)
{
    while (arg != 0)
    {
        arg -= 1;
    }
    return arg;
}

Corresponding code to generate such method is:

var methodContext = typeContext.Functors.Static("Test",
    [ParameterDefinition.Value<int>()], ResultDefinition.Value<int>());
var argument = methodContext.Argument<int>(0);
methodContext.While(
    methodContext.Expression(() =>
        argument.IsEqualTo(methodContext.Value(0)).Negate()),
    () => argument.SelfSubtract(1));
methodContext.Return(argument);