Re: Make GET_LISTENER take a pointer arg and deduce its type (issue 549890043 by address@hidden)

[dak]

On 2020/04/18 10:30:27, hanwenn wrote:
>
https://codereview.appspot.com/549890043/diff/579610043/lily/include/listener.hh
> File lily/include/listener.hh (left):
> 
>
https://codereview.appspot.com/549890043/diff/579610043/lily/include/listener.hh#oldcode140
> lily/include/listener.hh:140: #define GET_LISTENER(cl, proc)
get_listener
> (Callback_wrapper::make_smob<Listener::trampoline<cl, &cl::proc> > ())
> IMO, the problem is that the macro scopes 'proc' to come from 'cl',
which is
> magical. Couldn't we change the calling convention to be 
> 
>   ctx->GET_LISTENER(&SomeContext::func)

Nope.  For one thing, you should be happy Smob_core no longer needs to
provide a member function just for the sake of Listener, making Listener
less generic and introducing a compile-time dependency.  For another, it
requires the call site to spell out the type of the expression ctx.  And
the third is that the implementation still needs to derive SomeContext
from &SomeContext::func in order to meet the requirements of the
Callback_wrapper cell created.

> if we call this from within a SomeContext method itself, it could be 
> 
>    GET_LISTENER(&func)

No, it couldn't.  C++ member function pointer syntax cannot be done in
that manner.
 
> If so, would we need a macro at all?

The main purpose of the macro is not providing a wrapper for the
Listener creator, but rather for creating the template arguments for the
Callback_wrapper magic.  That one's the hardcore bit.  The Listener type
just curries two SCM values.

https://codereview.appspot.com/549890043/