What does 'inline' mean?

[Manu]

On Mon, Jun 8, 2020 at 6:50 PM Basile B. via Digitalmars-d <
digitalmars-d at puremagic.com> wrote:

> On Monday, 8 June 2020 at 06:14:44 UTC, Manu wrote:
> > Inline has been bugging me forever, it's usually not what I
> > want. The spec says this-or-that, but I think we should take a
> > step back, ignore what's written there, look at the problem
> > space, determine the set of things that we want, and then make
> > sure they're expressed appropriately.
> >
> > I think a first part of the conversation to understand, is that
> > since D doesn't really have first-class `inline` (just a
> > pragma, assumed to be low-level compiler control), I think most
> > people bring their conceptual definition over from C/C++, and
> > that definition is a little odd (although it is immensely
> > useful), but it's not like what D does.
> >
> > In C/C++, inline says that a function will be emit to the
> > binary only when
> > it is called, and the function is marked with internal linkage
> > (it is not
> > visible to the linker from the symbol table)
> > By this definition; what inline REALLY means is that the
> > function is not
> > placed in the binary where it is defined, it is placed in the
> > binary where
> > it is CALLED, and each CU that calls an inline function
> > receives their own
> > copy of the function. From here; optimisers will typically
> > inline the call
> > if they determine it's an advantage to do so.
> >
> > Another take on inline, and perhaps a more natural take (if
> > your mind is not poisoned by other native languages), is that
> > the function is not actually emit to an object anywhere, it is
> > rather wired directly inline into the AST instead of 'called'.
> > Essentially a form of AST macro.
>
> No. I rather see "inline" as a hint for the backend.
> DMD is peculiar with its way of inlining.
>
> > I reach for inline in C/C++ for various different reasons at
> > different times, and I'd like it if we were able to express
> > each of them:
> >
> > 1. I only want the function to be present in the CALLING
> > binary. I do not want an inline function present in the local
> > binary where it was defined (unless it was called internally).
> > I do not want a linker to see the inline function symbols and
> > be able to link to them externally. [This is about linkage and
> > controlling the binary or distribution environment]
>
> what if the function address is took in a delegate ?
> It still needs to be there, in the object matching to the CU
> where it is declared, otherwise there will be surprises, e.g
> &func in a CU and &func in another will have different addresses.


Right. This is fine and normal.
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