Discord.Net 3.0 Interface Design
This is mostly just a collection of notes for interface design for 3.0. As
such, don't expect them to be comprehensive or up to date.
Why no ITextChannel, IGuildChannel, etc?
Usually, it's better to design types in terms of the fields they have, rather
than using a discriminated union like the current IChannel interface.
However, the design chosen in 1.0 led to traits, which in C# was
notoriously hard to work with, debug and expand. Most notably, in
1.0.0-beta2, the internal implementation details were exposed in form of
SocketUserMessage, SocketTextChannel etc. simply to make consumption
easier. The effect of this has been that writing portable, re-usable code is
very hard, and has also caused us to be much slower when implementing updates
from Discord.
To simplify this, the current design has gone back to a centralised IChannel
type, a la D#+'s DiscordChannel implementation. However,
we are going to be using Nullable Reference Types to help reduce some
of the inevitable errors which will come around with a discriminated union
approach. Furthermore, this design allows in the future a traits-like system to
be implemented on top of it, once the design flaws have been worked out.
Future Plans
Ideally, shapes will become a thing, making the previous design much easier
to implement and maintain, on top of the current design. To give a small
example:
shape SChannel<T>
{
public ulong Id { get; }
}
shape SGuildChannel<T> : SChannel<T>
{
public ulong GuildId { get; }
public int? Position { get; }
public IEnumerable<PermissionOverwrite> PermissionOverwrites { get; }
public string Name { get; }
}
shape STextChannel<T> : SChannel<T>
{
public ulong? LastMessageId { get; }
public DateTimeOffset LastPinTimestamp { get; }
}
shape SGuildTextChannel<T> : SGuildChannel<T>, STextChannel<T>
{
public string? Topic { get; }
public bool IsNsfw { get; }
public int? RateLimit { get; }
}
public ValueTask<bool> DeleteLastMessageAsync<T>(T channel)
where T : STextChannel<T>
{
return channel.LastMessageId switch {
null => new ValueTask<bool>(false),
0 => new ValueTask<bool>(false),
_ => new ValueTask<bool>(DeleteMessageAsync(channel.LastMessageId))
};
static async Task<bool> DeleteMessage(ulong messageId)
{
var message = await GetMessageAsync(messageId);
if (message == null)
return false;
await message?.DeleteAsync();
return true;
}
}
Internally, DeleteLastMessageAsync will work on any channel, but as long
as that channel exposes the correct APIs, the above method will function as the
user expects.
Additionally, this provides a huge advantage in that the above code is
extremely easy to unit test; any type which fulfils the contract of
STextChannel<T> can be used, even if it doesn't implement the IChannel
interface.
