Monday, July 29, 2019

Digest for comp.lang.c++@googlegroups.com - 10 updates in 4 topics

ram@zedat.fu-berlin.de (Stefan Ram): Jul 29 04:10PM

>I think she is inspired by (possibly someone else who is inspired by) an
>article by the Go language creator.
 
One context where one would like to return a variant with
either a pointer to the active function or a sentinel value
is a trampoline (which can be used to user-implement TCO in
languages without it).
ram@zedat.fu-berlin.de (Stefan Ram): Jul 29 08:13PM

Supersedes: <trampoline-20190729170836@ram.dialup.fu-berlin.de>
[PS]
 
>I think she is inspired by (possibly someone else who is inspired by) an
>article by the Go language creator.
 
One context where one would like to return a variant with
either a pointer to the active function or a sentinel value
is a trampoline (which can be used to user-implement TCO in
languages without it).
 
PS: The above is not entirely correct. Actually, one wants
to return a newly created function for trampolining. Sorry!
Juha Nieminen <nospam@thanks.invalid>: Jul 29 02:25PM

> Surely it would have been better to not introduce a new keyword, and
> rather add another meaning for static. ;-)
 
Well, they used 'class' for strong enums, so "typedef class"?
"Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>: Jul 29 06:00PM +0200

On 29.07.2019 16:25, Juha Nieminen wrote:
>> Surely it would have been better to not introduce a new keyword, and
>> rather add another meaning for static. ;-)
 
> Well, they used 'class' for strong enums, so "typedef class"?
 
Sounds nice but that syntax already has a meaning.
 
On the third hand, `auto` also already had a meaning.
 
 
Cheers!,
 
- Alf
Bonita Montero <Bonita.Montero@gmail.com>: Jul 29 01:49PM +0200

I need a class-function / method that returns a function-pointer
to the same type of class-function. How do I implement this? I
need this to have a kind of state-machine where each state-func-
tion returns a pointer to the next state function. I.e I would
write: "while( (fn = state->*fn()) != nullptr );". I see no way
to define the type of fn since it is recursive.
"Öö Tiib" <ootiib@hot.ee>: Jul 29 06:30AM -0700

On Monday, 29 July 2019 14:49:58 UTC+3, Bonita Montero wrote:
> tion returns a pointer to the next state function. I.e I would
> write: "while( (fn = state->*fn()) != nullptr );". I see no way
> to define the type of fn since it is recursive.
 
Perhaps there are no way to make a function that return function
pointer of its own type. However I do not understand the need
of it. There is state and there is its handler and if you
really need conversions between state and handler then you may
make conversion constructors/operators ... but in my humble
opinion it feels a bit messy and confusing. Here is example:
 
#include <iostream>
 
// state
class State
{
public:
using Handler = State (*)(int);

State(Handler h)
:handler_(h)
{ }

operator Handler() {return handler_;}

private:
Handler handler_;
};

// example handlers
State DoSomethingA(int param);

State DoSomethingB(int param);

// example of usage
int main()
{
State::Handler s(DoSomethingA(0));
s = s(1);
s = s(2);
s = s(3);
s = s(4);
}

// implementations of handlers
State DoSomethingA(int param)
{
std::cout << "A: " << param << '\n';
return DoSomethingB;
}

State DoSomethingB(int param)
{
std::cout << "B: " << param << '\n';
return DoSomethingA;
}
 
If it does miss what you asked for then post actual
example code what are your handlers and what usage
are you trying to achieve.
"Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>: Jul 29 05:59PM +0200

On 29.07.2019 15:30, Öö Tiib wrote:
 
> Perhaps there are no way to make a function that return function
> pointer of its own type. However I do not understand the need
> of it.
 
I think she is inspired by (possibly someone else who is inspired by) an
article by the Go language creator.
 
As I recall his examples work nicely in Go, or assembly language, or a
more dynamic language like Python, but have to be rewritten with some
indirection for a language with strong static type checking like C++.
 
The reason for doing it that way, in languages where it's simple, is the
textual simplicity of the source code. Since it doesn't give that
textual simplicity in C++, it's not a good way in C++. It's doable, just
not in any practical way.
 
 
Cheers!,
 
- Alf
guinness.tony@gmail.com: Jul 29 01:16AM -0700


> But i need to understand if loads with older stores to the same location have total order in relaxed memory model of ARM CPU ?
 
> And i need to know if stores to the same location have total order in relaxed memory model of ARM CPU ?
 
> And i need to understand if stores with older loads to the same location have total order in relaxed memory model of ARM CPU ?
 
RTFM.
 
And stop spamming comp.programming.threads
Juha Nieminen <nospam@thanks.invalid>: Jul 29 02:26PM


>> And i need to understand if stores with older loads to the same location have total order in relaxed memory model of ARM CPU ?
 
> RTFM.
 
> And stop spamming comp.programming.threads
 
I would not classify asking on-topic questions as "spamming".
Bonita Montero <Bonita.Montero@gmail.com>: Jul 29 04:32PM +0200

>> And stop spamming comp.programming.threads
 
> I would not classify asking on-topic questions as "spamming".
 
Posting a lot of redundant stuff which no one would read because
there s nothing new in it is spamming. And there is a substantial
part of his postings which is not related to threading.
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