build failure with -std=c++17 and pari

[isuruf]

paridecl.h has long rank(GEN x);, but there's also std::rank in C++11.

When

#include <string>
using namespace std;

is done in libsrc/eclib/parifact.h, std::rank is pulled in to the namespace with gcc 7.3. (doesn't happen with gcc 4.9)

This leads to a build failure,

<PREFIX>/include/pari/paridecl.h:1442:19: error: return type specified for deduction guide
 long    rank(GEN x);
                   ^
<PREFIX>/include/pari/paridecl.h:1442:1: error: decl-specifier in declaration of deduction guide
 long    rank(GEN x);
 ^~~~
<PREFIX>/include/pari/paridecl.h:1442:19: error: 'long' or 'short' invalid for '__dguide_rank'
 long    rank(GEN x);
                   ^
<PREFIX>/include/pari/paridecl.h:1442:9: error: deduction guide for 'std::rank< <template-parameter-1-1> >' must have trailing return type
 long    rank(GEN x);

cc @saraedum

[saraedum]

Building the master branch here from source, I could not reproduce this:
make -j4 CXXFLAGS="-std=c++11" worked for me with GCC 8.2.1.

[saraedum]

Setting -std=c++17 gives me the original error.

[isuruf]

This error might go away if we stopped doing using namespace std, but that's a lot of code to change.

[saraedum]

I'm not a C++ expert but I think this is the way this type of problem is handled usually. Of course, we could also force an older C++ standard but I guess that's not such a great idea in the long run.

[isuruf]

It might not be enough. Ran into this in lcalc as well.

[isuruf]

It is enough.

Following produces an error

#include <string.h>
using namespace std;

#include <pari/pari.h>
int main() {

}

Following doesn't

#include <string.h>

#include <pari/pari.h>
int main() {

}

[JohnCremona]

I have never wanted to not have a global std namespace sine it seemed ridiculous to have to write std::cout instead of cout for every output line -- and many more. I also do not relish the prospect of changing almost every line of code for such a trivial reason.

Instead: since almost no symbols from libpari are used, would it be possible to wrap the header file which include pari.h into a different namespace called pari? Then I would not mind inserting pari:: in a few places.

[isuruf]

@JohnCremona, how about doing using std::cout; and whatever eclib need in a central place? Then you can use cout in other places. This prevents std::rank getting pulled in as rank.

[isuruf]

Instead: since almost no symbols from libpari are used, would it be possible to wrap the header file which include pari.h into a different namespace called pari?

This is not possible since pari is including standard headers and they'll be pulled in to the pari namespace and cause issues.

[JohnCremona]

I spent hours, perhaps days, on reorganising the header files earlier this year. I am not going to spend more time on that now, as I have more important things to do.

[isuruf]

Here's a patch that fixes this. Do you think it's reasonable? (If so, I can send it as a PR.)

diff --git a/libsrc/bitspace.cc b/libsrc/bitspace.cc
index 377f03c..8620145 100644
--- a/libsrc/bitspace.cc
+++ b/libsrc/bitspace.cc
@@ -25,7 +25,7 @@
 #include <eclib/interface.h>
 #include <eclib/bitspace.h>
 
-using namespace std;
+
 
 bitspace::bitspace(long d)
 {
diff --git a/libsrc/eclib/curvesort.h b/libsrc/eclib/curvesort.h
index d32a408..ee710e2 100644
--- a/libsrc/eclib/curvesort.h
+++ b/libsrc/eclib/curvesort.h
@@ -26,7 +26,8 @@
                            //flags that this file has been included
 
 #include <string>
-using namespace std;
+#include <eclib/templates.h>
+
 
 #define USE_NEW_CODE_LETTERS
 
diff --git a/libsrc/eclib/interface.h b/libsrc/eclib/interface.h
index 7b3cac6..0facfc3 100644
--- a/libsrc/eclib/interface.h
+++ b/libsrc/eclib/interface.h
@@ -47,7 +47,7 @@
 #include <ext/numeric>
 #endif
 #include <iterator>
-using namespace std;
+
 #include <eclib/templates.h>
 #include <stdint.h>
 
diff --git a/libsrc/eclib/options.h b/libsrc/eclib/options.h
index b35998e..52457de 100644
--- a/libsrc/eclib/options.h
+++ b/libsrc/eclib/options.h
@@ -27,7 +27,7 @@
 
 #include <eclib/GetOpt.h>
 #include <iostream>
-using namespace std;
+
 
 #define DEFAULT_QUIET 0
 #define DEFAULT_VERBOSE 1
diff --git a/libsrc/eclib/parifact.h b/libsrc/eclib/parifact.h
index d577546..e026125 100644
--- a/libsrc/eclib/parifact.h
+++ b/libsrc/eclib/parifact.h
@@ -26,7 +26,7 @@
                            //flags that this file has been included
 
 #include <string>
-using namespace std;
+#include <eclib/templates.h>
 
 string factor(const string n);
 int is_prime(const string p);
diff --git a/libsrc/eclib/templates.h b/libsrc/eclib/templates.h
index 81fba60..89d2da5 100644
--- a/libsrc/eclib/templates.h
+++ b/libsrc/eclib/templates.h
@@ -29,7 +29,45 @@
 #include <set>
 #include <vector>
 #include <iterator>
-using namespace std;
+#include <complex>
+#include <limits>
+#include <map>
+#include <unordered_map>
+#include <algorithm>
+#include <iomanip>
+
+using std::string;
+using std::vector;
+using std::cout;
+using std::cerr;
+using std::cin;
+using std::endl;
+using std::flush;
+using std::ios;
+using std::ostream;
+using std::istream;
+using std::ifstream;
+using std::stringstream;
+using std::istringstream;
+using std::ostringstream;
+using std::ofstream;
+using std::ios_base;
+using std::numeric_limits;
+using std::ostream_iterator;
+using std::complex;
+using std::ws;
+using std::skipws;
+using std::map;
+using std::unordered_map;
+using std::min;
+using std::max;
+using std::ptr_fun;
+using std::pair;
+using std::sort;
+using std::abs;
+using std::binary_function;
+using std::setw;
+
 
 template <class T >
 inline ostream& operator<<(ostream& os, const vector<T>& v)
diff --git a/libsrc/kbessel.cc b/libsrc/kbessel.cc
index add08c6..01cebf0 100644
--- a/libsrc/kbessel.cc
+++ b/libsrc/kbessel.cc
@@ -24,7 +24,8 @@
 
 #include <iostream>  // for debugging only
 #include <cmath>
-using namespace std;
+
+#include <eclib/templates.h>
 #include <eclib/kbessel.h>
 #ifndef M_LN2
 #define M_LN2   0.69314718055994530942
diff --git a/libsrc/parifact.cc b/libsrc/parifact.cc
index 85b6905..4cfffc4 100644
--- a/libsrc/parifact.cc
+++ b/libsrc/parifact.cc
@@ -29,7 +29,7 @@
 //#define DEBUG_GPFACT
 
 #include <iostream>
-using namespace std;
+
 
 string
 factor(const string n)
diff --git a/libsrc/version.cc b/libsrc/version.cc
index 71d369d..20035b6 100644
--- a/libsrc/version.cc
+++ b/libsrc/version.cc
@@ -22,8 +22,8 @@
 //////////////////////////////////////////////////////////////////////////
  
 #include <iostream>
+#include <eclib/templates.h>
 
-using namespace std;
 
 void show_version()
 {

[JohnCremona]

Thank you -- that looks very much simpler than I thought it would be. I had also thought that the line "using namespace std;" only appeared in one place in a file (interface.h) which was included by just about every other file, but that turns out to be far from the truth.

Please make a PR and I will test.