[Swift-devel] Standard library

[Mihael Hategan]

On Sat, 2015-01-10 at 22:57 -0600, Tim Armstrong wrote:
> > Am I missing something?
> >
> I think the problem I was thinking of is the combination of function
> overloading and keyword arguments - then you have a number of possible
> function signatures that grows exponentially with the number of optional
> arguments.  It's not so bad if it's purely positional arguments since then
> you can just treat a function with n optional arguments as n + 1 overloads
> of the function.

I'm not sure. You should be able to statically determine which keyword
arguments are passed in a given call, fill the missing ones with nulls
or default values, sort, and generate a call to a single purely
positional underlying implementation.

> 
> It might take a bit of implementation work to get to work with the other
> function type checking logic in Swift/T, but it seems tractable.  It's
> already a bit complicated trying to work out the input types of the
> function arguments when there's the possibility of type variables, option
> types, etc.

Shouldn't polymorphism come before fancy type stuff? :)

> 
> There are some weird corner cases.  For example, which implementation of
> avg would this call?
> avg([]);

Unless there is some mechanism that can ensure that it doesn't matter,
or a mechanism allowing you to overload based on specific values (like
pattern matching), then you probably have to have a way to say exactly
which function should be called. Java requires you to do an explicit
cast of arguments that would otherwise result in ambiguity.

Mihael