Still in development, but if you are interested into looking around,
start with


     swigtypemaps.swg

which is the head file. Also read the docs for %fragments in 

     fragments.swg 

and follow the definitions in one of the supported languages:

     python, perl, ruby, tcl


/* -----------------------------------------------------------------------------
 *  Internal typemap specializations
 * ----------------------------------------------------------------------------- */


carrays.swg		Implement the carrays.i library
cdata.swg		Implement the cdata.i library
cmalloc.swg		Implement the cmalloc.i library
cpointer.swg		Implement the cpointer.i library
cstring.swg		Implement the cstring.i library typemaps for char *
cwstring.swg		Implement the cstring.i library typemaps for wchar_t *
exception.swg		Implement the exception.i library
implicit.swg		Allow the use of implicit C++ constructors

string.swg		Typemaps for char * string
wstring.swg		Typemaps for wchar_t * string
std_string.swg		Typemaps for std::string
std_wstring.swg		Typemaps for std::wstring
swigtype.swg		Typemaps for the SWIGTYPE type
void.swg		Typemaps for the 'void' type
enumint.swg		Typemaps for enums treated as 'int' 
swigobject.swg		Typemaps for the SWIG_Object as in PyObject, Tcl_Obj, etc.
misctypes.swg		Typemaps for miscellaneos types (size_t, ptrdiff_t, etc)
ptrtypes.swg		Typemaps for types with a 'ptr' behavior
valtypes.swg		Typemaps for 'by value' types
inoutlist.swg		IN/OUTPUT/INOUT typemaps, where the OUTPUT values are returned in a list
primtypes.swg		Common macros to manage primitive types (short,int,double,etc)

cstrings.swg		Common macros to implemented the cstring/cwstring libraries
std_strings.swg		Common macros to implemented the std::string/std::wstring typemaps
strings.swg		Common macros and typemaps for string and wstring (char *, wchar_t *)

swigmacros.swg		Basic macros 
fragments.swg		Macros for fragment manipulations


typemaps.swg		The old typemaps.i library, not needed anymore