Re: C++11 - Parameter pack question

Re: C++11 - Parameter pack question

[Marc Glisse]

On Fri, 15 Aug 2014, Sidney Marshall wrote:

> The following code compiles and runs correctly but gives a warning:
>
> ----------------------------------------
> #include<iostream>
>
> using namespace std;
>
> template<class T>
> T sum(T value) {
>  return value;
> }
>
> template<class T, class ... U>
> auto sum(T value, U ... values) {
>    return value + sum(values ...);
> }
>
> int main() {
>  cout << sum(1, 2, 4.6) << endl;
>  cout << sum(1, "abcde", 2) << endl;
> }
> --------------------------------------
>
> $ g++ -std=c++11 pack.cpp
> pack.cpp:11:31: warning: â??sumâ?? function uses â??autoâ?? type specifier 
> without trailing return type [enabled by default]
> auto sum(T value, U ... values) {

The warning should probably specify that this is a C++14 feature. You 
should be compiling with -std=c++1y.

-- 
Marc Glisse

Re: C++11 - Parameter pack question

[Sidney Marshall]

At 09:12 AM 8/16/2014 +0200, Marc Glisse wrote:
>On Fri, 15 Aug 2014, Sidney Marshall wrote:
>
>>The following code compiles and runs correctly but gives a warning:
>>
>>----------------------------------------
>>#include<iostream>
>>
>>using namespace std;
>>
>>template<class T>
>>T sum(T value) {
>>  return value;
>>}
>>
>>template<class T, class ... U>
>>auto sum(T value, U ... values) {
>>    return value + sum(values ...);
>>}
>>
>>int main() {
>>  cout << sum(1, 2, 4.6) << endl;
>>  cout << sum(1, "abcde", 2) << endl;
>>}
>>--------------------------------------
>>
>>$ g++ -std=c++11 pack.cpp
>>pack.cpp:11:31: warning: â??sumâ?? function 
>>uses â??autoâ?? type specifier without trailing 
>>return type [enabled by default]
>>auto sum(T value, U ... values) {
>
>The warning should probably specify that this is 
>a C++14 feature. You should be compiling with -std=c++1y.

You are correct - I didn't read section 7.1.6.4 
paragraphs 2 and 5 of the standard correctly. Thank you.

I guess I can't write this function in C++11 this way.


>--
>Marc Glisse

--Sidney Marshall

Re: C++11 - Parameter pack question

[Sidney Marshall]

At 09:12 AM 8/16/2014 +0200, Marc Glisse wrote:
>On Fri, 15 Aug 2014, Sidney Marshall wrote:
>
>>The following code compiles and runs correctly but gives a warning:
>>
>>----------------------------------------
>>#include<iostream>
>>
>>using namespace std;
>>
>>template<class T>
>>T sum(T value) {
>>  return value;
>>}
>>
>>template<class T, class ... U>
>>auto sum(T value, U ... values) {
>>    return value + sum(values ...);
>>}
>>
>>int main() {
>>  cout << sum(1, 2, 4.6) << endl;
>>  cout << sum(1, "abcde", 2) << endl;
>>}
>>--------------------------------------
>>
>>$ g++ -std=c++11 pack.cpp
>>pack.cpp:11:31: warning: â??sumâ?? function 
>>uses â??autoâ?? type specifier without trailing 
>>return type [enabled by default]
>>auto sum(T value, U ... values) {
>
>The warning should probably specify that this is 
>a C++14 feature. You should be compiling with -std=c++1y.

You are correct - I didn't read section 7.1.6.4 
paragraphs 2 and 5 of the standard correctly. Thank you.

I guess I can't write this function in C++11 this way.


>--
>Marc Glisse

--Sidney Marshall

C++11 - Parameter pack question

[Sidney Marshall]

Hello,

The following code compiles and runs correctly but gives a warning:

----------------------------------------
#include<iostream>

using namespace std;

template<class T>
T sum(T value) {
   return value;
}

template<class T, class ... U>
auto sum(T value, U ... values) {
     return value + sum(values ...);
}

int main() {
   cout << sum(1, 2, 4.6) << endl;
   cout << sum(1, "abcde", 2) << endl;
}
--------------------------------------

$ g++ -std=c++11 pack.cpp
pack.cpp:11:31: warning: ‘sum’ function uses 
‘auto’ type specifier without trailing return type [enabled by default]
  auto sum(T value, U ... values) {

$ ./a.exe
7.6
de
-------------------------------------------

All of my attempts to use a trailing return type 
failed (and I believe should have failed according to the standard).

My two questions:

1. What possible user mistake is the warning worried about?

2. How can I write my code with better style so that there is no warning?

Thank you.

--Sidney Marshall

C++11 - Parameter pack question

[Sidney Marshall]

Hello,

The following code compiles and runs correctly but gives a warning:

----------------------------------------
#include<iostream>

using namespace std;

template<class T>
T sum(T value) {
   return value;
}

template<class T, class ... U>
auto sum(T value, U ... values) {
     return value + sum(values ...);
}

int main() {
   cout << sum(1, 2, 4.6) << endl;
   cout << sum(1, "abcde", 2) << endl;
}
--------------------------------------

$ g++ -std=c++11 pack.cpp
pack.cpp:11:31: warning: ‘sum’ function uses 
‘auto’ type specifier without trailing return type [enabled by default]
  auto sum(T value, U ... values) {

$ ./a.exe
7.6
de
-------------------------------------------

All of my attempts to use a trailing return type 
failed (and I believe should have failed according to the standard).

My two questions:

1. What possible user mistake is the warning worried about?

2. How can I write my code with better style so that there is no warning?

Thank you.

--Sidney Marshall