Wednesday, March 23, 2016

Digest for comp.lang.c++@googlegroups.com - 25 updates in 6 topics

Jerry Stuckle <jstucklex@attglobal.net>: Mar 22 07:38PM -0400

On 3/22/2016 7:12 PM, Öö Tiib wrote:
> lot more often than composition. We can not solve a OOP question if
> square is kind of rectangle or not by uttering such religious slogans
> and suggesting that rectangle is component of square. ;)
 
Yes, a square is a more specific instance of a rectangle, just like a
rectangle is a more specific instance of a parallelogram. And that is a
more specific instance of a quadrilateral.
 
--
==================
Remove the "x" from my email address
Jerry Stuckle
jstucklex@attglobal.net
==================
woodbrian77@gmail.com: Mar 22 06:51PM -0700

On Tuesday, March 22, 2016 at 6:13:07 PM UTC-5, Öö Tiib wrote:
 
> That "composition over inheritance" is IMHO a mantra. It has a kernel
> of good truth in it but that is turned into religious slogan. Religious
> slogans are considered harmful.
 
The national motto of the United States is "In G-d we trust."
 
 
Brian
Ebenezer Enterprises
http://webEbenezer.net
"Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>: Mar 23 05:24AM +0100


> The national motto of the United States is "In G-d we trust."
 
The adoption of it as a national motto happened at the same time as
segregation was abolished. Which would place it around 1956, if memory
serves me right. Anyway you can google it.
 
I think it was a fair exchange at the time: adopt a lunatic national
motto, a motto which after all had appeared on flags and coins earlier,
but get rid of segregation − or at least a good start on that.
 
However, now with a black US President the time may have come to finally
get rid also of the since 1956 state-endorsed lunacy. The Founding
Fathers did not want that: they would have been shocked to know it was
adopted. Unfortunately it's been reaffirmed by voting many times in
recent years, and most Americans are in favor of it. :(
 
 
Cheers & hth.,
 
- Alf
scott@slp53.sl.home (Scott Lurndal): Mar 23 01:35PM


>The national motto of the United states is
 
"Out of many, one" (act of congress, 1782).
"Öö Tiib" <ootiib@hot.ee>: Mar 23 01:08PM -0700

> > of good truth in it but that is turned into religious slogan. Religious
> > slogans are considered harmful.
 
> The national motto of the United States is "In G-d we trust."
 
I meant "religious" in sense of "dogmatic" or "superstitious". Sort of
like "build a wall".
woodbrian77@gmail.com: Mar 23 02:36PM -0700

On Wednesday, March 23, 2016 at 3:09:14 PM UTC-5, Öö Tiib wrote:
 
> > The national motto of the United States is "In G-d we trust."
 
> I meant "religious" in sense of "dogmatic" or "superstitious". Sort of
> like "build a wall".
 
Walls are important for privacy and private property. I'm
a posterboy for walls in terms of closed source. Without
that wall, I'd be left to the whims of "leaders" like Obama.
 
 
Brian
Ebenezer Enterprises
http://webEbenezer.net
Christof Warlich <christof.warlich1@gmail.com>: Mar 23 06:49AM -0700

Hi,
 
I'm trying to understand how to use functors with std::bind().
 
The following code defines a simple example class named "Offset" to instantiate three different functors being used to calculate its "result" member variable in three increasingly complex scenarios:
 
#include <functional>
#include <iostream>
 
struct Offset {
Offset(int offset): offset(offset) {}
void operator()(int value) {
result = offset + value;
}
int result;
private:
int offset;
};
 
int main() {
 
// scenario 1
Offset offset10(10);
offset10(100);
std::cout << "offset10(100) yields result "
<< offset10.result
<< std::endl;
 
// scenario 2
std::function<void(int)> offset20(Offset(20));
offset20(100);
std::cout << "offset20(100) yields result "
<< offset20.target<Offset>()->result
<< std::endl;
 
// scenario 3
std::function<void()> offset100by30 = std::bind(Offset(30), 100);
offset100by30();
std::cout << "offset100by30() yields result "
//<< offset100by30.???->result
<< std::endl;
 
return 0;
}
 
My issue is with scenario 3, i.e. when using std::bind(): How could I access the result member variable in this case?
 
Please note that this is a contrived example to simplify things: I _do_ need a solution where Offset is passed as a temporary as shown, i.e. passing it as a reference would not be an option.
 
Thanks for any help,
 
Chris
"Öö Tiib" <ootiib@hot.ee>: Mar 23 01:44PM -0700

On Wednesday, 23 March 2016 15:49:56 UTC+2, Christof Warlich wrote:
 
> return 0;
> }
 
> My issue is with scenario 3, i.e. when using std::bind(): How could I access > the result member variable in this case?
 
The type returned by 'std::bind' is of unspecified Callable type that is
not required to have any methods of extracting what was bound into it.
 
 
> Please note that this is a contrived example to simplify things: I _do_
> need a solution where Offset is passed as a temporary as shown, i.e.
> passing it as a reference would not be an option.
 
You assume a solution but do not describe a problem that it solves.
What is the benefit of using 'std::bind'? I felt it as sort of obsolete
with lambdas available.
Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk>: Mar 22 11:54PM

Someone should make a post-apocalyptic comic about a world where Donald
Trump was voted President and Jeremy Corbyn Prime Minister.
 
I think they should call the comic "Radioactive Sausages".
 
/Flibble
"Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>: Mar 23 01:24AM +0100

On 23.03.2016 00:54, Mr Flibble wrote:
> Someone should make a post-apocalyptic comic about a world where Donald
> Trump was voted President and Jeremy Corbyn Prime Minister.
 
> I think they should call the comic "Radioactive Sausages".
 
You should read Robert Heinlein's "Friday", Leigh.
 
It's not Friday yet.
 
In the novel Friday is a female Artifical Person whose vocation is the
time honored one of assassin. Her "family", that she's bought into,
disavows her when they find out she's an AP. Assassin is OK, but AP? Oh
noes. There's something about her employer, I don't recall, but anyway
she's on the run because WWIII has broken out, and it's a corporate war
of terrorist attacks, assassinations, stock market manipulation,
politics, and not the least, deception and large scale propaganda.
 
Physical money is being outlawed, in order to be able to track
undesirables and possible problematic persons like her.
 
Oh dang, that sounds familiar. Well. :)
 
 
Cheers!,
 
- Alf
 
PS: I think Ben Bova also covered much the same angle on things.
woodbrian77@gmail.com: Mar 22 07:44PM -0700

On Tuesday, March 22, 2016 at 6:55:03 PM UTC-5, Mr Flibble wrote:
> Trump was voted President and Jeremy Corbyn Prime Minister.
 
> I think they should call the comic "Radioactive Sausages".
 
> /Flibble
 
 
I like Ted Cruz. He would be an old school President --
hard working and humble. We need another decent President.
Actually, the West needs another decent President. Please
pray for Brussels and Paris.
 
 
Brian
Ebenezer Enterprises
http://webEbenezer.net
"Chris M. Thomasson" <nospam@nospam.nospam>: Mar 22 09:38PM -0700


> Someone should make a post-apocalyptic comic about a world where Donald
> Trump was voted President and Jeremy Corbyn Prime Minister.
 
> I think they should call the comic "Radioactive Sausages".
 
Humm...
 
http://southpark.cc.com/full-episodes/s19e02-where-my-country-gone
 
;^)
scott@slp53.sl.home (Scott Lurndal): Mar 23 01:37PM

>time honored one of assassin. Her "family", that she's bought into,
>disavows her when they find out she's an AP. Assassin is OK, but AP? Oh
>noes. There's something about her employer, I don't recall, but anyway
 
Kettle Belly Baldwin. From an earlier Heinlein short "Gulf", originally.
 
 
>Physical money is being outlawed, in order to be able to track
>undesirables and possible problematic persons like her.
 
>Oh dang, that sounds familiar. Well. :)
 
_If this goes on..._ may be a more illustrative heinlein example of what might
happen if Cruz or Trump win (only 4 years late compared to the 2012 election in
the story).
Gareth Owen <gwowen@gmail.com>: Mar 23 07:08PM


>> /Flibble
 
> I like Ted Cruz. He would be an old school President --
> hard working and humble. We need another decent President.
 
Really?
 
Because almost everyone who's ever met him - especially former
classmates and Republicans who had to work him - thinks he's a total
asshole. And "humble" is absolutely not one of the words they use.
 
"If you killed Ted Cruz on the floor of the Senate, and the trial was in
the Senate, nobody would convict you." -- Lindsey Graham
Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk>: Mar 23 07:12PM

> Please
> pray for Brussels and Paris.
 
Praying achieves absolutely nothing; if you really cared then you would
do more than something that achieves absolutely nothing.
 
/Flibble
Gareth Owen <gwowen@gmail.com>: Mar 23 08:08PM

>> Please
>> pray for Brussels and Paris.
 
> Praying achieves absolutely nothing
 
Not true. It makes the pray-er feel better about themselves.
woodbrian77@gmail.com: Mar 23 01:28PM -0700

On Wednesday, March 23, 2016 at 2:09:10 PM UTC-5, gwowen wrote:
> asshole. And "humble" is absolutely not one of the words they use.
 
> "If you killed Ted Cruz on the floor of the Senate, and the trial was in
> the Senate, nobody would convict you." -- Lindsey Graham
 
To his credit, Lindsey Graham has changed his mind and started
fund raising for Ted Cruz. There's an article about that on
www.dailywire.com .
 
Brian
Ebenezer Enterprises
http://webEbenezer.net
"Chris M. Thomasson" <nospam@nospam.nospam>: Mar 23 01:29PM -0700


> > I think they should call the comic "Radioactive Sausages".
 
> Humm...
 
> http://southpark.cc.com/full-episodes/s19e02-where-my-country-gone
 
This episode is kind of amusing because a "Trump" like
character is elected president of Canada, and builds a
wall along the border with America. This character then
pisses off basically everybody, and Canada is quickly
thrown into disarray, with tumbleweeds blowing through
the damn streets! Not nuclear war, but its still a bit
interesting to me.
 
;^)
Bob Langelaan <bobl0456@gmail.com>: Mar 23 11:36AM -0700

My students are normally able to figure out on their own any issues that arise while doing their assignments. But I had 3 different students run into this issue this semester and end up having to reach out to me for help. I believe that this is mostly caused by their inability to map the error message to their solution.
 
Here is a very simplified version of the issue:
 
class myClass
{
const int i;
};
 
int main()
{
myClass a, b;
a = b;
}
 
The code above generates 3 errors in MS VS 2015, all of which refer to "attempting to reference a deleted function".
 
I must admit it took me a while to find the issue the first time. Realize that the code the student sent me was much more involved than the example above.
 
Of course it can be argued that it is very rare (never?) that you would actually want to define and initialize a non-const data member in a class interface file. But these are students just learning the language and relatively new to object oriented programming as well and as such are more likely to make to make such a logic error (not defining a const member as static).
 
My point is that students would be more likely to able to figure the issue on their own if the MS VS 2015 error messages were more illuminating.
Bob Langelaan <bobl0456@gmail.com>: Mar 23 11:42AM -0700

On Wednesday, March 23, 2016 at 11:37:03 AM UTC-7, Bob Langelaan wrote:
 
> I must admit it took me a while to find the issue the first time. Realize that the code the student sent me was much more involved than the example above.
 
> Of course it can be argued that it is very rare (never?) that you would actually want to define and initialize a non-const data member in a class interface file. But these are students just learning the language and relatively new to object oriented programming as well and as such are more likely to make to make such a logic error (not defining a const member as static).
 
> My point is that students would be more likely to able to figure the issue on their own if the MS VS 2015 error messages were more illuminating.
 
 
There was an error in my original post. I meant to say (corrected part in CAPS):
 
Of course it can be argued that it is very rare (never?) that you would actually want to define and initialize a CONST DATA MEMBER WHICH IS NOT STATIC in a class interface file. But these are students just learning the language and relatively new to object oriented programming as well and as such are more likely to make to make such a logic error (not defining a const member as static).
Ian Collins <ian-news@hotmail.com>: Mar 24 08:28AM +1300

On 03/24/16 07:36, Bob Langelaan wrote:
> }
 
> The code above generates 3 errors in MS VS 2015, all of which refer
> to
"attempting to reference a deleted function".
 
Firstly, please wrap your lines!
 
Second try using an alternative compiler. The two I use make the cause
much clearer:
 
CC -std=c++14 ~/temp/c.cc
"/home/ian/temp/c.cc", line 8: Error: a must be initialized.
"/home/ian/temp/c.cc", line 8: Error: Constant members of 'myClass' must
be initialized.
"/home/ian/temp/c.cc", line 8: Error: b must be initialized.
"/home/ian/temp/c.cc", line 8: Error: Constant members of 'myClass' must
be initialized.
"/home/ian/temp/c.cc", line 9: Error: Using deleted function
'myClass::operator=(const myClass&)'.
 
and:
 
g++ -std=c++14 ~/temp/c.cc
/home/ian/temp/c.cc: In function 'int main()':
/home/ian/temp/c.cc:8:10: error: use of deleted function
'myClass::myClass()'
myClass a, b;
^
/home/ian/temp/c.cc:1:7: note: 'myClass::myClass()' is implicitly
deleted because the default definition would be ill-formed:
class myClass
^
/home/ian/temp/c.cc:1:7: error: uninitialized const member in 'class
myClass'
/home/ian/temp/c.cc:3:12: note: 'const int myClass::i' should be initialized
const int i;
^
/home/ian/temp/c.cc:8:13: error: use of deleted function
'myClass::myClass()'
myClass a, b;
^
/home/ian/temp/c.cc:9:4: error: use of deleted function 'myClass&
myClass::operator=(const myClass&)'
a = b;
^
/home/ian/temp/c.cc:1:7: note: 'myClass& myClass::operator=(const
myClass&)' is implicitly deleted because the default definition would be
ill-formed:
class myClass
^
/home/ian/temp/c.cc:1:7: error: non-static const member 'const int
myClass::i', can't use default assignment operator
 
--
Ian Collins
ram@zedat.fu-berlin.de (Stefan Ram): Mar 23 04:13AM

>Inheritance is fundamental to object oriented paradigm
 
What is fundamental is, er, polymorphism.
 
Implementation inheritance can be used to implement polymorphism,
but polymorphism can also be implemented by interface inheritance
or by duck typing (pure run-time typing).
 
Actually, the last way is the historic way of Smalltalk. Static
types were then added to add additional compile-time type safety.
 
>composition is fundamental to any software design paradigm
 
By the way, there is not only inheritance and composition,
but also delegation. Delegation is not just another name for
composition, but a special pattern that »simulates« more
properties of inheritance, delegation is based on composition,
but it goes beyond mere composition (see Gamma et al.).
 
>We can not solve a OOP question if
>square is kind of rectangle or not
 
When we have a /source/ for squares, this can also be seen as
a source for rectangles.
 
That is, if one defines
 
auto isSquare = []( auto x ){ return x.getWidth() == x.getHeight(); }
auto isRectangle = []( auto x ){ return true; }
 
then isSquare( x ) implies isRectangle( x ).
 
(Simplified: »Every square is a rectangle.«)
 
When we have a /sink/ for rectangles, this can also be seen as
a sink for squares. That is, we can use an object with the
interface
 
struct rectangle_sink
{ virtual void setWidth( int width ) = 0;
virtual void setHeight( int height ) = 0; };
 
as a sink for a square as follows:
 
sink.setWidth( square.getExtension() );
sink.setHeight( square.getExtension() );
 
(Simplified: »Every rectangle is a square.«)
 
. However, when something is /both/ a source and a sink, then
neither is a subset of the other.
ram@zedat.fu-berlin.de (Stefan Ram): Mar 23 02:02PM

>std::function<void()> offset100by30 = std::bind(Offset(30), 100);
>I _do_ need a solution where Offset is passed as a temporary
 
If want to access a member of it after it has been
evaluated, it can't be a temporary.
ram@zedat.fu-berlin.de (Stefan Ram): Mar 23 07:13PM

> myClass a, b;
> a = b;
>}
 
The compiler would usually create an assignment
function:
 
my_class & operator=( const my_class & x)
{ i = x.i; return *this; }
 
. In this function, an assignment to a read-only member
is attempted. This would be ill-formed. So this assignment
operator becomes implicitly deleted.
wij@totalbb.net.tw: Mar 22 11:34PM -0700

Xn project (version 0.03) is released.
https://sourceforge.net/projects/systemnode/
 
Xn project tries to develop a nodal language protocol capable for
almost all kinds of data storage and communication.
Written languages can be in any natural language, can be various
kind of file format, executable scripts (even alive).
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