[swift-evolution] Proposal: Allow operators to have parameters with default values

Tony Allevato tony.allevato at gmail.com
Thu Nov 2 19:34:48 CDT 2017

I like this idea as it's presented here, for the debugging/logging reasons
that you stated.

Should we tighten the shackles a little be to validate that *only* the
special #file/#line/#function directives can be permitted for these extra
parameters? I'm struggling to think of a case where we would want to allow
something else, since there's no way to provide the values for them in a
standard call.

On Thu, Nov 2, 2017 at 5:26 PM Dave DeLong via swift-evolution <
swift-evolution at swift.org> wrote:

> Hi SE,
> As I’ve been using my own custom operators like “?!”, “!!”, or operators
> provided by libraries (<|, ~>, etc), I’ve often wanted to capture the #file
> and #line where the operators are used to make debugging their use a lot
> easier.
> For example, given something the unwrap-or-die operator (
> https://github.com/erica/swift-evolution/blob/2c1be72e34c970894e4ba7ed9df5cee3298d4282/proposals/XXXX-unwrap-or-die.md),
> you’d want to capture the #file and #line so you could pass it on to the
> underlying call to fatalError().
> Or, if you’re using a custom bind operator and something goes wrong, it’d
> be great to be able to capture the file and line where the operator is used
> so you can quickly triage the bug in your code.
> Unfortunately, Swift has the hard limit the the implementations of unary
> operators may have one-and-only-one parameter, and that binary operators
> may only have two parameters.
> I’d like to propose a very minor change to Swift, whereby operator
> implementations may have more than their one or two parameters, provided
> that all subsequent parameters come with a default value. This would make
> it trivial to add in #file, #line, #function, etc to your operator
> implementations, which you can then capture for your own purposes.
> An implementation of this change, with passing tests, can be found here:
> https://github.com/davedelong/swift/commit/c65c634a59b63add0dc9df1ac8803e9d70bfa697
> Dave
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> swift-evolution at swift.org
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