Bug#672035: [Swig-user] Using own string class

[David Piepgrass]

> At ZNC we have an own string class CString, which is inherited from 
> std::string.
> The goal is to use it as a just string in target languages.
>
> How to do that properly?

When you use a string class derived from std::string, the main problem tends to 
be that SWIG's built-in typemaps refer to std::string explicitly, but that's 
unnecessary. For some target languages (at least C# and Java) if you simply 
make a copy of the typemap with std::string changed to $*1_ltype, then you can 
%apply those typemaps to your derived class. For example, here are the 
corrected typemaps for Java:

namespace std {
// Changed lines are marked "//fixed"
%typemap(in) const string &
%{ if(!$input) {
     SWIG_JavaThrowException(jenv, SWIG_JavaNullPointerException, "String param 
cannot be null");
     return $null;
   }
   const char *$1_pstr = (const char *)jenv->GetStringUTFChars($input, 0); 
   if (!$1_pstr) return $null;
   $*1_ltype $1_str($1_pstr); //fixed
   $1 = &$1_str;
   jenv->ReleaseStringUTFChars($input, $1_pstr); %}

%typemap(directorout,warning=SWIGWARN_TYPEMAP_THREAD_UNSAFE_MSG) const string &
%{ if(!$input) {
     SWIG_JavaThrowException(jenv, SWIG_JavaNullPointerException, "String param 
cannot be null");
     return $null;
   }
   const char *$1_pstr = (const char *)jenv->GetStringUTFChars($input, 0); 
   if (!$1_pstr) return $null;
   /* possible thread/reentrant code problem */
   static $1_ltype $1_str; //fixed
   $1_str = $1_pstr;
   $result = &$1_str;
   jenv->ReleaseStringUTFChars($input, $1_pstr); %}
} // namespace std

Then you use %apply to support your custom string too:

%apply std::string { CString }
%apply std::string& { CString& } // [not supported in Java]
%apply const std::string& { const CString& }