/// <summary>
/// Implements a <see cref="ISpecializationCacheArgs"/> interface in order to
/// make the given <paramref name="typeBuilder"/> compatible with a
/// <see cref="SpecializationCache{TLoader, TArgs, TDelegate}"/> instance.
/// </summary>
/// <param name="typeBuilder">The target type builder to use.</param>
/// <param name="fields">The source fields used for implementation.</param>
private static void ImplementSpecializationCacheArgs(
TypeBuilder typeBuilder,
FieldInfo[] fields)
{
var specializedType = typeof(SpecializedValue <>);
var getArgMethod = typeBuilder.DefineMethod(
nameof(ISpecializationCacheArgs.GetSpecializedArg),
MethodAttributes.Public | MethodAttributes.Virtual,
typeof(object),
new Type[] { typeof(int) });
var emitter = new ILEmitter(getArgMethod.GetILGenerator());
// Declare labels and emit jump table
var labels = new ILLabel[fields.Length];
for (int i = 0, e = fields.Length; i < e; ++i)
{
labels[i] = emitter.DeclareLabel();
}
emitter.Emit(OpCodes.Ldarg_1);
emitter.EmitSwitch(labels);
for (int i = 0, e = fields.Length; i < e; ++i)
{
var field = fields[i];
emitter.MarkLabel(labels[i]);
emitter.Emit(OpCodes.Ldarg_0);
emitter.Emit(OpCodes.Ldfld, field);
// Wrap in a specialized instance
var fieldReturnType = specializedType.MakeGenericType(field.FieldType);
var instanceConstructor = fieldReturnType.GetConstructor(
new Type[]
{
field.FieldType
});
emitter.EmitNewObject(instanceConstructor);
emitter.Emit(OpCodes.Box, fieldReturnType);
emitter.Emit(OpCodes.Ret);
}
// Return dummy argument
emitter.Emit(OpCodes.Ldnull);
emitter.Emit(OpCodes.Ret);
emitter.Finish();
typeBuilder.AddInterfaceImplementation(typeof(ISpecializationCacheArgs));
}