C# Generic Method – Exception Handling for Unacceptable Type Parameters

cnet

When the value of a normal parameter is unacceptable (and the requirements can't be checked completely at compile time), we check at runtime and throw an ArgumentException if the check fails.

When the "value" of a type parameter is similarly unacceptable, what kind of exception do we throw? Are there any guidelines on this?

(Note: If I try ArgumentException, ReSharper wants to complain – which makes me think there may be another kind of exception that's recommended for this.)

Best Answer

There isn't a native exception in the .NET Framework for "Invalid Type Parameter Argument." Jon Skeet asked about this on Stack Overflow, and ultimately decided to write his own:

#region License and Terms
// Unconstrained Melody
// Copyright (c) 2009-2011 Jonathan Skeet. All rights reserved.
// 
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// 
//     http://www.apache.org/licenses/LICENSE-2.0
// 
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#endregion

using System;
using System.Runtime.Serialization;

namespace UnconstrainedMelody
{
    /// <summary>
    /// Exception thrown to indicate that an inappropriate type argument was used for
    /// a type parameter to a generic type or method.
    /// </summary>
    public class TypeArgumentException : Exception
    {
        /// <summary>
        /// Constructs a new instance of TypeArgumentException with no message.
        /// </summary>
        public TypeArgumentException()
        {
        }

        /// <summary>
        /// Constructs a new instance of TypeArgumentException with the given message.
        /// </summary>
        /// <param name="message">Message for the exception.</param>
        public TypeArgumentException(string message)
            : base(message)
        {
        }

        /// <summary>
        /// Constructs a new instance of TypeArgumentException with the given message and inner exception.
        /// </summary>
        /// <param name="message">Message for the exception.</param>
        /// <param name="inner">Inner exception.</param>
        public TypeArgumentException(string message, Exception inner)
            : base(message, inner)
        {
        }

        /// <summary>
        /// Constructor provided for serialization purposes.
        /// </summary>
        /// <param name="info">Serialization information</param>
        /// <param name="context">Context</param>
        protected TypeArgumentException(SerializationInfo info, StreamingContext context) : base(info, context)
        {
        }
    }
}
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