public static T Add<T>(T left, T right) { return left + right; }People have come up with a large number of solutions, but they all have their own problems, ranging from messy looking syntax to less-than-optimal performance (particularly due to virtual function calls). The solution I propose is a somewhat hacky one (yes that's a word) which maintains both good performance and clean looking code: write the function in IL.
The code for the add method boils down to something like this:
ldarg.0 ldarg.1 add retFor those not familiar with IL, the above code adds the first to arguments of the method, then returns the result.
I found that this actually works with generic types. No funny errors, no nothing. Of course, I didn't actually compile any IL source code - I wrote a separate program to generate the assembly. The source code for it is this:
namespace Generator { using System; using System.Linq; using System.Reflection; using System.Reflection.Emit; public static class Program { public static void Main() { var assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(new AssemblyName("Operations"), AssemblyBuilderAccess.Save); var module = assemblyBuilder.DefineDynamicModule("Operations", "Operations.dll"); var type = module.DefineType("Operator", TypeAttributes.Public | TypeAttributes.Sealed); type.DefineBinaryOperatorMethod("Add", OpCodes.Add); type.DefineBinaryOperatorMethod("Subtract", OpCodes.Sub); type.DefineBinaryOperatorMethod("Multiply", OpCodes.Mul); type.DefineBinaryOperatorMethod("Divide", OpCodes.Div); type.DefineBinaryOperatorMethod("Remainder", OpCodes.Rem); type.CreateType(); assemblyBuilder.Save("Operations.dll"); } private static MethodBuilder DefineBinaryOperatorMethod(this TypeBuilder type, string name, OpCode operation) { var method = type.DefineMethod(name, MethodAttributes.Public | MethodAttributes.Static); var genericParameter = method.DefineGenericParameters("T").First(); genericParameter.SetBaseTypeConstraint(typeof(ValueType)); method.SetReturnType(genericParameter); method.SetParameters(genericParameter, genericParameter); method.DefineParameter(1, ParameterAttributes.None, "left"); method.DefineParameter(2, ParameterAttributes.None, "right"); var ilGenerator = method.GetILGenerator(); var continueLabel = ilGenerator.DefineLabel(); ilGenerator.Emit(OpCodes.Ldtoken, genericParameter); ilGenerator.EmitCall(OpCodes.Call, typeof(Type).GetMethod("GetTypeFromHandle"), null); ilGenerator.EmitCall(OpCodes.Callvirt, typeof(Type).GetProperty("IsPrimitive").GetGetMethod(), null); ilGenerator.Emit(OpCodes.Brtrue_S, continueLabel); ilGenerator.Emit(OpCodes.Ldstr, "The specified type is not supported by this operation."); ilGenerator.Emit(OpCodes.Newobj, typeof(ArgumentException).GetConstructor(new[] { typeof(string) })); ilGenerator.Emit(OpCodes.Throw); ilGenerator.MarkLabel(continueLabel); ilGenerator.Emit(OpCodes.Ldarg_0); ilGenerator.Emit(OpCodes.Ldarg_1); ilGenerator.Emit(operation); ilGenerator.Emit(OpCodes.Ret); return method; } } }In case your wondering what the ldtoken/call/callvirt/brtrue.s/ldstr/newobj/throw stuff is doing there, that just checks to make sure the type argument is a primitive type (yes this only works on primitive types), and throws an ArgumentException otherwise. Before adding that, .NET threw some pretty nasty exceptions when I tried it on some non-primitive types.
As a final note, the methods generated with indeed work on all primitive types. Even booleans. I was surprised to get a DivideByZeroException upon attempting this:
Operator.Divide(true, false);Again, this only works on primitive types. Remember, string and decimal are not primitive types. Perhaps this could be extended to calling the op_* functions...
After a couple small performance tests, I found that this method was nearly as fast as doing simple addition (x + y). Then again, I know nothing about microbenchmarks. Try it for yourself :D
Enjoy
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