[swift-evolution] [Completing Generics]

[Douglas Gregor]

> On Mar 9, 2016, at 4:28 AM, Erik Verbruggen <erik.verbruggen at me.com> wrote:
> 
> 
>> Generic constants
>> 
>> let constants could be allowed to have generic parameters, such that they produce differently-typed values depending on how they are used. For example, this is particularly useful for named literal values, e.g.,
>> 
>> let π<T : FloatLiteralConvertible>: T = 3.141592653589793238462643383279502884197169399
>> 
>> The Clang importer could make particularly good use of this when importing macros.
> 
> I assume the following will fall under "constant expression":
> 
> 	let 2π = 2 * π

That would involve inferring that 2π is a generic constant… could certainly be something to explore, but it’s somewhat new territory. 

> 
> Also, how does the clang-importer handle:
> 
> 	#define M_DOUBLE_PI (2 * M_PI)
> 
> Or rephrasing, this is specifically for the case where the initialiser only consists of a single literal token?

I was thinking of it in terms of a single literal token, but I’m pointing out the feature as a possibility, not doing the detailed design work that would be involved in making it real. It’s possible we could make the importer smarter in this regard.

	- Doug


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