Discussion Thread: DIP 1030--Named Arguments--Final Review

[Steven Schveighoffer]

On 5/14/20 9:20 AM, jmh530 wrote:
> On Thursday, 14 May 2020 at 12:03:13 UTC, Petar Kirov [ZombineDev] wrote:
>> [snip]
>>
>> [1]:
>> /sandbox/main.d(5): Error: `library.copy` called with argument types 
>> `(string, string)` matches both:
>> /sandbox/library.d(1):     `library.copy(string source, string 
>> destination)`
>> and:
>> /sandbox/library.d(7):     `library.copy(string source, string 
>> distinasion)`
> 
> Interesting that it only mentions two of them and not all of them. If 
> you comment one of them out, then it mentions the other.
> 
> To your suggestion above, it's unclear if you are suggesting that the 
> compiler read the deprecation message and change behavior somehow based 
> on it. There is nothing stopping you from providing detailed deprecation 
> messages today. Expanding on Seb's example, you could have something 
> like below.
> 
> void foo(int x, int y) { ... }
> 
> deprecated("Parameters renamed: `xVal` -> `x` | `yVal` -> `y`")
> extern(D, argNames)
> void foo(int xVal, int yVal) { ... }
> 
> The extern(D, argNames) is from Seb and is what would tell the compiler 
> to only allow calling foo with keyword arguments.
> 
> Thinking on it, you could make this even more general and have
> extern(D, positionOnly)
> extern(D, keywordOnly)
> which would force either positionOnly or keywordOnly syntax. That would 
> resolve any concerns that I have.

I don't think the extern(D, argNames) idea works. Both foos are mangled 
exactly the same, so you would have identical symbols in the object file.

However, one COULD provide a prototype simply for renaming parameters 
(without implementation). I don't think you even need a specialized 
extern(D, argNames) marking, if the compiler will just prefer 
non-deprecated matches over deprecated ones.

-Steve