[API Proposal]: new System.ComponentModel.TimeOnlyConverter class

[0xced]

Background and motivation

Converting between System.TimeOnly and string 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 etc.) so I think System.TimeOnly would be a welcome addition.

I was expecting this to work, but converting from string actually throws:

System.NotSupportedException: TypeConverter cannot convert from System.String.

TypeConverter timeOnlyConverter = TypeDescriptor.GetConverter(typeof(TimeOnly));
TimeOnly? time = timeOnlyConverter.ConvertFromString("7:00") as TimeOnly?;

Having built-in support for type conversion would probably help to drive adoption of the relatively new TimeOnly type.

Addressing this issue would fix #59253 which is mentioned in System.Runtime work planned for .NET 7 (but only under the Backlog list, not the Planned for .NET 7 list).

Note that a similar proposal for the System.DateOnly type has been filed as #68743.

API Proposal

public class TimeOnlyConverter : System.ComponentModel.TypeConverter
{
    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);
    public override bool IsValid(System.ComponentModel.ITypeDescriptorContext? context, object? value);
}

API Usage

Using the converter would most likely happen through TypeDescriptor.GetConverter(typeof(TimeOnly)):

var timeOnlyConverter = TypeDescriptor.GetConverter(typeof(TimeOnly));
var time = timeOnlyConverter.ConvertFromString("7:00") as TimeOnly?;

or even through a higher level abstractions such as Microsoft.Extensions.Configuration.Binder (which also uses TypeDescriptor.GetConverter internally) as described in #64739:

var configuration = new ConfigurationBuilder()
    .AddInMemoryCollection(new Dictionary<string, string> { ["BreakfastTime"] = "7:00:00" })
    .Build();
var breakfastTime = configuration.GetValue<TimeOnly>("BreakfastTime");

It could also be used by directly creating a TimeOnlyConverter instance but this is a less likely scenario:

var timeOnlyConverter = new System.ComponentModel.TimeOnlyConverter();
var time = timeOnlyConverter.ConvertFromString("7:00") as TimeOnly?;

Alternative Designs

To the best of my knowledge, there's no alternative design that would make sense for adding a new System.ComponentModel.TypeConverter.

Risks

System.ComponentModel.TimeOnlyConverter being a new class, no risks are introduced.

[ghost]

Tagging subscribers to this area: @dotnet/area-system-componentmodel
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Background and motivation

Converting between System.TimeOnly and string 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 etc.) so I think System.TimeOnly would be a welcome addition.

I was expecting this to work, but converting from string actually throws:

System.NotSupportedException: TypeConverter cannot convert from System.String.

TypeConverter timeOnlyConverter = TypeDescriptor.GetConverter(typeof(TimeOnly));
TimeOnly? time = timeOnlyConverter.ConvertFromString("7:00") as TimeOnly?;

Having built-in support for type conversion would probably help to drive adoption of the relatively new TimeOnly type.

Addressing this issue would fix #59253 which is mentioned in System.Runtime work planned for .NET 7 (but only under the Backlog list, not the Planned for .NET 7 list).

Note that a similar proposal for the System.DateOnly type has been filed as #68743.

API Proposal

public class TimeOnlyConverter : System.ComponentModel.TypeConverter
{
    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);
    public override bool IsValid(System.ComponentModel.ITypeDescriptorContext? context, object? value);
}

API Usage

Using the converter would most likely happen through TypeDescriptor.GetConverter(typeof(TimeOnly)):

var timeOnlyConverter = TypeDescriptor.GetConverter(typeof(TimeOnly));
var time = timeOnlyConverter.ConvertFromString("7:00") as TimeOnly?;

or even through a higher level abstractions such as Microsoft.Extensions.Configuration.Binder (which also uses TypeDescriptor.GetConverter internally) as described in #64739:

var configuration = new ConfigurationBuilder()
    .AddInMemoryCollection(new Dictionary<string, string> { ["BreakfastTime"] = "7:00:00" })
    .Build();
var breakfastTime = configuration.GetValue<TimeOnly>("BreakfastTime");

It could also be used by directly creating a TimeOnlyConverter instance but this is a less likely scenario:

var timeOnlyConverter = new System.ComponentModel.TimeOnlyConverter();
var time = timeOnlyConverter.ConvertFromString("7:00") as TimeOnly?;

Alternative Designs

To the best of my knowledge, there's no alternative design that would make sense for adding a new System.ComponentModel.TypeConverter.

Risks

System.ComponentModel.TimeOnlyConverter being a new class, no risks are introduced.

Author:	0xced
Assignees:	-
Labels:	api-suggestion, area-System.ComponentModel, untriaged
Milestone:	-

[tarekgh]

@0xced please move this proposal with the one in #68743. Feel free to close this one after merging the proposals. Thanks!

[0xced]

I have just amended #68743 to cover both DateOnly and TimeOnly, so I'm closing this one.