• 3 Posts
  • 221 Comments
Joined 1 year ago
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Cake day: July 3rd, 2023

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  • Here’s a real world side project example of how I handle this situation:

     public IResult<T> GetResourceValue<T>(string path)
        {
            string err = $"{typeof(T).FullName} is not available from this Resource ({nameof(FileSystemResource)})";
    
            switch (typeof(T))
            {
                case Type t when t == typeof(DriveInfo):
                    return (IResult<T>)new Ok<DriveInfo>(BackingValue);
                case Type t when t == typeof(DirectoryInfo):
                    err = $"Directory path invalid: {path}";
                    var dir = new DirectoryInfo(path);
    
                    if (dir.Exists)
                        return (IResult<T>)new Ok<DirectoryInfo>(dir);
                    break;
                case Type t when t == typeof(FileInfo):
                    err = $"File path invalid: {path}";
                    var file = new FileInfo(path);
    
                    if (file.Exists)
                        return (IResult<T>)new Ok<FileInfo>(file);
                    break;
            }
            return new Error<T>(err);
        }
    

    You said elsewhere that it feels like you’re doing something wrong if you have to check for every type just to use a Generic. I think you’re right in thinking along those lines. There should be a minimal number of types to check, and Ideally limited via a type constraint.

    Here’s example that includes a constraint:

        public IResult<T> GetValue<T>() where T : struct =>
            typeof(T) switch
            {
                Type t when t == typeof(int) && value <= int.MaxValue =>
                 (IResult<T>)new Ok<int>((int)value),
                Type t when t == typeof(uint) && value <= uint.MaxValue && value >= uint.MinValue =>
                 (IResult<T>)new Ok<uint>((uint)value),
                Type t when t == typeof(byte) && value <= byte.MaxValue && value >= byte.MinValue =>
                 (IResult<T>)new Ok<byte>((byte)value),
                Type t when t == typeof(sbyte) && value <= (int)sbyte.MaxValue =>
                 (IResult<T>)new Ok<sbyte>((sbyte)value),
                Type t when t == typeof(short) && value <= (int)short.MaxValue =>
                 (IResult<T>)new Ok<short>((short)value),
                Type t when t == typeof(ushort) && value <= ushort.MaxValue =>
                 (IResult<T>)new Ok<ushort>((ushort)value),
                Type t when t == typeof(long) && value <= long.MaxValue =>
                 (IResult<T>)new Ok<long>((long)value),
                Type t when t == typeof(ulong) => (IResult<T>)new Ok<int>((int)value),
                _ => new IntegerError<T>()
            };