Proposal: new System.ComponentModel.EncodingConverter class

[0xced]

Rationale and Usage

Converting between System.Text.Encoding and string or int is currently not supported using a System.ComponentModel.TypeConverter. Many system types are supported out of the box (System.DateTimeOffset, System.Guid, System.TimeSpan, System.Uri, System.Version etc.) so I think System.Text.Encoding would be a welcome addition.

I was expecting this to work, but converting from string or int actually throws a NotSupportedException.

using System.ComponentModel;
using System.Diagnostics;
using System.Text;
TypeConverter encodingConverter = TypeDescriptor.GetConverter(typeof(Encoding));
Encoding utf8EncodingFromString = encodingConverter.ConvertFromString("utf-8") as Encoding;
Encoding utf8EncodingFromInt = encodingConverter.ConvertFrom(65001) as Encoding;

Proposed API

public partial class EncodingConverter : System.ComponentModel.TypeConverter
{
    public EncodingConverter();
    public override bool CanConvertFrom(System.ComponentModel.ITypeDescriptorContext context, System.Type sourceType);
    public override bool CanConvertTo(System.ComponentModel.ITypeDescriptorContext context, System.Type destinationType);
    public override object ConvertFrom(System.ComponentModel.ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value);
    public override object ConvertTo(System.ComponentModel.ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value, System.Type destinationType);
}

Details

Converting from string or int to System.Text.Encoding is straightforward using Encoding.GetEncoding, implementation would be very similar to the VersionConverter pull request (dotnet/corefx#28516) merged about one month ago.

Open Questions

• Should converting from int (interpreted as a code page) be supported ? I started writing unit tests and noticed a lot of edge cases:
  • If supporting conversion from int, should we also support conversion from all types implicitly convertible to int, i.e. sbyte, byte, short, ushort and char ? (Yes in my opinion)
  • If supporting conversion from int, should we support conversion from larger types, such as long when the value fits an int, e.g. long codePage = 1200. (Yes in my opinion)
  • If supporting conversion from int, should we support conversion int as string, e.g. string codePage = "1200" ? (This is where I started to wonder if supporting conversion from int was a good idea at all)

Pull Request

A pull request with the proposed changes is available: dotnet/corefx#32527

[ericstj]

There's nothing blocking you from creating this yourself today outside the framework. We'd need to see some significant use cases our community demand to add this to the framework.