Thoughts on throw helpers

Question

To reduce redundant code, I have some throw helper methods:

protected static X ThrowInvalidOperation(string operation, X a, X b) {
    throw new InvalidOperationException("Invalid operation: " + a.type.ToString() + " " + operation + " " + b.type.ToString());
}

Usage:

    public static X operator +(X a, X b) {
        if (...) {
            return new X(...);
        }
        return ThrowInvalidOperation("+", a, b);
    }

Problem: Because the operator + must always return a value, I fixed this by making ThrowInvalidOperation return a value and call it with returnThrowInvalidOperation("+", a, b);

There a many disadvatages - one is because I can't call it from a method returning a different type.
I wish there is there a way to mark the helper function "always throws a exception", so the compiler stops tracking return values.

Q: What possibilities do I have to make this work?

Answer 1

Make the exception:

protected static Exception MakeInvalidOperation(string operation, X a, X b)
{
    return new InvalidOperationException(
        "Invalid operation: " + a.type + " " + operation + " " + b.type);
}

Then throw it:

throw MakeInvalidOperation("+", a, b);

You're in good company:

// Type: Microsoft.Internal.Web.Utils.ExceptionHelper
// Assembly: WebMatrix.Data, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
// MVID: 3F332B40-45DB-42E2-A4ED-0826DE223A79
// Assembly location: C:\Windows\Microsoft.NET\assembly\GAC_MSIL\WebMatrix.Data\v4.0_1.0.0.0__31bf3856ad364e35\WebMatrix.Data.dll

using System;

namespace Microsoft.Internal.Web.Utils
{
    internal static class ExceptionHelper
    {
        internal static ArgumentException CreateArgumentNullOrEmptyException(string paramName)
        {
            return new ArgumentException(CommonResources.Argument_Cannot_Be_Null_Or_Empty, paramName);
        }
    }
}

Although it's not that much code to write your own custom Exception-based type (or InvalidOperationException-based) and define some constructor that formats a message for you.

To reduce redundant code

When I hear this, I think AOP which is implemented quite well by PostSharp. If you have lots of redundant code you should consider AOP, but bear in mind that it might be overkill.