[Proposal] Enum.IsDefined()

[benaadams]

Code for https://github.com/dotnet/corefx/issues/10692

So rather than doing this:

string DoTheThing(MyEnum argument)
{
    if (!Enum.IsDefined(typeof(MyEnum), argument))
    {
         Log.Warn(...);
         return String.Empty;
    }
    return argument.ToString();
}

You can do this:

string DoTheThing(MyEnum argument)
{
    if (!argument.IsDefined())
    {
         Log.Warn(...);
         return String.Empty;
    }
    return argument.ToString();
}

Enum.IsDefined(typeof(MyEnum), argument) is also quite slow as it needs to do lots of conversion checks etc; whereas if you already have the enum these don't need to be done.

e.g.
https://github.com/dotnet/corefx/blob/master/src/System.Private.Uri/src/System/UriExt.cs#L19-L24

[omariom]

When it is about 20-30 items in an array it is faster to just iterate over it.

[benaadams]

Closing as proposal, not active PR