We need something like source_location in D

[guy hebert]

On Wednesday, 31 July 2019 at 06:31:40 UTC, Manu wrote:
> On Tue, Jul 30, 2019 at 11:31 PM Manu <turkeyman at gmail.com> 
> wrote:
>>
>> On Tue, Jul 30, 2019 at 11:29 PM Manu <turkeyman at gmail.com> 
>> wrote:
>> >
>> > On Tue, Jul 30, 2019 at 8:55 PM Nicholas Wilson via 
>> > Digitalmars-d <digitalmars-d at puremagic.com> wrote:
>> > >
>> > > On Wednesday, 31 July 2019 at 01:39:05 UTC, Andrej 
>> > > Mitrovic wrote:
>> > > > From C++20: 
>> > > > http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1208r5.pdf
>> > > >
>> > > > Instead of having to constantly declare "file = 
>> > > > __FILE__, line = __LINE__" everywhere, it would be so 
>> > > > much more useful to just have a single built-in type 
>> > > > which we can default initialize . For example:
>> > > >
>> > > > -----
>> > > > import std.algorithm;
>> > > >
>> > > > void checkAndThrow (lazy bool expression, Loc loc =
>> > > > __LOCATION__)
>> > > > {
>> > > >     if (!expression)
>> > > >         throw new Exception("Failed", loc.file, 
>> > > > loc.line);
>> > > > }
>> > > >
>> > > > void main ()
>> > > > {
>> > > >     auto arr = [1, 1, 1, 1];
>> > > >     checkAndThrow(arr.sum == 4);
>> > > >
>> > > >     // should throw with file+line of this statement
>> > > >     checkAndThrow(arr.sum == 5);
>> > > > }
>> > > > -----
>> > > >
>> > > > This also makes it very easy to extend in the future, 
>> > > > because we don't have to pollute the namespace with a 
>> > > > lot of "__"-style symbols.
>> > > >
>> > > > The actual naming of the location symbol is something we 
>> > > > can bikeshed over, that's fine.
>> > > >
>> > > > If you grep for `string file = __FILE__, size_t line = 
>> > > > __LINE__` or `string file = __FILE__, int line = 
>> > > > __LINE__`, it is everywhere in Druntime and Phobos. I 
>> > > > think it's time we got rid of this repetition.
>> > > >
>> > > > I know __traits(getLocation) got implemented recently, 
>> > > > but it's not very useful in this context because it 
>> > > > returns a tuple 
>> > > > (https://github.com/dlang/dmd/pull/10013). I don't see 
>> > > > an easy way to use it in function parameters.
>> > >
>> > > It returning a tuple is not the problem because they auto 
>> > > expand :
>> > >
>> > > void foo(string a, int b, int c)
>> > > {
>> > >      import std.stdio;
>> > >      writeln(a, " ", b);
>> > > }
>> > > void main()
>> > > {
>> > >      foo(__traits(getLocation,foo));
>> > > }
>> > >
>> > > That you can't pass the caller loc is.
>> > >
>> > > A DIP will take a long time, I don't think the addition of 
>> > > __SYMBOLS__ require one. The addition of a type will 
>> > > possibly be problematic, but if  `Loc` were a tuple that 
>> > > would be fine if we could do
>> > >
>> > > void foo(auto a = 1);
>> > >
>> > > since it would be just as silly to have to type
>> > >
>> > > void foo(typeof(__LOCATION__) loc =  __LOCATION__);
>> >
>> > Make a `Loc` type in the library:
>> >
>> > struct Loc
>> > {
>> >   string file;
>> >   int line;
>> >   int column;
>> > }
>> >
>> > Make a helper to construct one:
>> >
>> > template getLoc(alias symbol)
>> > {
>> >   enum getLoc = return Loc(__traits(getLocation, symbol));
>> > }
>>
>> I refactored my original idea and left it broken... it should 
>> be this:
>>
>> enum getLoc = Loc(__traits(getLocation, symbol));
>
> 3rd time's the charm!
>
> enum getLoc(alias symbol) = Loc(__traits(getLocation, symbol));

Yes,that's very interesting stuff to know about. Thank you so 
much for the valuable information.