What does 'inline' mean?

[Andrei Alexandrescu]

On 6/13/20 12:08 AM, Manu wrote:
> On Sat, Jun 13, 2020 at 2:05 PM Walter Bright via Digitalmars-d 
> <digitalmars-d at puremagic.com <mailto:digitalmars-d at puremagic.com>> wrote:
> 
>     On 6/12/2020 8:25 PM, Andrei Alexandrescu wrote:
>      > On 6/12/20 8:54 PM, Walter Bright wrote:
>      >> On 6/12/2020 5:17 PM, Andrei Alexandrescu wrote:
>      >>> Not sure about that part - if linkage was static by means of
>     using the
>      >>> "static" keyword, multiple definitions may not be merged. (I
>     may be wrong,
>      >>> please correct me.) Consider:
>      >>>
>      >>> static inline int fun() {
>      >>>      static int x;
>      >>>      return ++x;
>      >>> }
>      >>>
>      >>> In C++, each translation unit containing a definition of fun()
>     will have a
>      >>> distinct address for x. I don't see how the bodies of those
>     functions can be
>      >>> merged.
>      >>
>      >> They are not merged in D, for the simple reason that
>     ModuleA.fun() and
>      >> ModuleB.fun() will have different (mangled) names presented to
>     the linker.
>      >
>      > For D the question is if they are merged if the function is
>     defined in a .di
>      > file and imported in two other modules.
> 
>     If the di file is mentioned on the command line to the compiler
> 
> 
> It's not, that's literally the point of a .di file.
> 
>     , yes (1)
>     instance of it appears in the executable. Otherwise, (0) instances
>     of it appear
>     in the executable. There are never 2 or more instances in the
>     executable.
> 
> 
> Exactly. And this is not a useful design.

All I can say is if that and/or other wrinkles prevent header-only 
libraries definition and use, yes, not a useful design.

So Manu, is the top-level goal "I want header-only libraries in D"?