Units of Measurement Library: units-d

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On Friday, 1 April 2016 at 22:54:53 UTC, Simen Kjaeraas wrote:
> On Friday, 1 April 2016 at 21:46:35 UTC, ag0aep6g wrote:
>> On 01.04.2016 22:59, Simen Kjaeraas wrote:
>>> The usual way to fix it would be to include __FILE__ and 
>>> __LINE__ in the
>>> template arguments:
>>
>> Right, no mixin this way. I wouldn't call this "truly nice", 
>> though.
>>
>> It depends on code formatting to work. Put everything on one 
>> line and it breaks. Significant whitespace is a pain when 
>> generating code. Though this is not nearly as bad as 
>> significant indentation, of course.
>>
>> __FILE__ also kind of breaks separate compilation. All object 
>> files have to be compiled from the same directory. Otherwise 
>> __FILE__ will be different.
>>
>> __LINE__ has a similar (maybe even more obscure) issue. Add or 
>> remove a newline before compiling dependent modules and things 
>> break. Usually, one recompiles all dependents when a 
>> dependency changes, but a significant newline, really?
>
> I kinda agree. And looking at 
> https://dlang.org/spec/traits.html, I see there's __MODULE__, 
> which would probably be a better choice than __FILE__.
>
> As for __LINE__, what we'd want is basically something like 
> __CONTEXT__, which doesn't exist, but might be the .mangleof of 
> the surrounding scope:
>
> struct S(string ctx = __CONTEXT__) {
>     pragma(msg, ctx);
> }
>
> S!() a; // "3foo"
>
> void bar() {
>     S!() b; // "_D3foo3barFZv"
> }
>
> struct S2 {
>     S!() c; // "S3foo2S2"
>     void baz() {
>         S!() d; // "_D3foo2S23bazMFZv"
>     }
> }
>
> That'd remove the problem of significant whitespace. In fact, 
> it'd also eliminate the need for __MODULE__ in this case.
>
> Still though, that's not enough if we want this to work:
>
> void foo() {
>     alias a = Foo!(); alias b = Foo!();
>     assert(!isSame!(a, b));
> }
>
> We could also add __COLUMN__, which would be the horizontal 
> index of the instantiation's beginning:
>
>     foo(3, Bar!3.baz);
> //         ^Here. Position 11.
>
> Next problem:
>
> void main() {
>     pragma(msg, __LINE__);
>     mixin("pragma(msg, __LINE__);\npragma(msg, __LINE__);");
>     pragma(msg, __LINE__);
> }
>
> That prints '4' twice - once for the actual line 4, the other 
> for the second line of the mixin. However, __FILE__ is 
> different, so I guess __CONTEXT__ could also be.
>
> --
>   Simen

What is needed is Lisp's gensym construct.