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TIL (meaning, Tonight I Learned) that you can declare non-optional parameters after optional ones in C#.
Just create an indexer with optional parameters:
int this[int a, string b = "b"] { get; set; }
The IL for the set method is this:
instance void set_Item (
int32 a,
[opt] string b,
int32 'value'
) cil managed
{
.param [2] = "b"
}
Note that the "value" is after b.
@jasonbock Or you can use the attributes instead of the C# syntax
@meziantou well....actually, interestingly enough, what you just posted may save my butt :)
@meziantou It seems to address most of my cases, unless someone does this:
int this[string a, CancellationToken b = default] { get; set; }
Which, yes, is bizarre, but legal C#. I can't figure out a way to use those attributes to state that I want the default of CancellationToken. That'll probably end up being an edge cases that in all likelihood will never happen (famous last words :) ).
@jasonbock The C# compiler doesn't allow it as it validates the type of the value in the parameter, but the VB.NET and F# compilers are ok... I think you can open an issue on Roslyn if this scenario is important for your use case
@meziantou I think I'll just have to work around it. The edge case this shows up is....really edgey :). An indexer setter where a parameter is optional with default. With what I'm doing, I think I can come up with something to move things around.