DIP 1020--Named Parameters--Community Review Round 2

rikki cattermole rikki at cattermole.co.nz
Thu Sep 12 12:06:47 UTC 2019

On 12/09/2019 11:50 PM, Yuxuan Shui wrote:
> On Thursday, 12 September 2019 at 11:46:46 UTC, rikki cattermole wrote:
>> On 12/09/2019 11:29 PM, Yuxuan Shui wrote:
>>> Dumb question: @named parameters are ignored in overload resolution, 
>>> so in this example:
>>> void draw(@named Circle shape);
>>> void draw(@named Rectangle shape);
>>> Is a call to draw:
>>> draw(someShape);
>>> always going to be a compilation error?
>> Yes.
>> Because you didn't use a named argument.
>> These would have been valid declarations that would match that 
>> function call:
>> void draw(Circle shape);
>> void draw(Rectangle shape);
>> In this example you didn't need named parameters.
>> Since the variable name of the calling body should be descriptive 
>> enough to tell you that it is a circle/rectangle.
> Ah, sorry. I meant to write draw(shape: someShape).

In that case, two methods:

1. void draw(Shape)(@named Shape shape) { draw(shape); }

2. void draw(Shape:Circle)(@named Shape shape) { draw(shape); }

The second is better because of validating the parameter type, but does 
require one per type. Assuming I remember this particular bit of 
templates correctly.

I had to assume that drawing has to be specific to the type passed in 
and that the draw function will be concrete (can be virtual). But that 
shouldn't be a problem.

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