Hello!
Some people claim that extending GiNaC is "unnecessary complex" (see e.g.
http://www.ginac.de/pipermail/ginac-list/2006-July/000882.html). So I
think it is good idea to provide self-contained, minimalistic example
of a GiNaC class. The actual code is copy/pasted from the tutorial.
---
doc/examples/Makefile.am | 3 +-
doc/examples/mystring.cpp | 104 +++++++++++++++++++++++++++++++++++++++++++++
doc/tutorial/ginac.texi | 3 +-
3 files changed, 108 insertions(+), 2 deletions(-)
diff --git a/doc/examples/Makefile.am b/doc/examples/Makefile.am
index 5ee2c5d..e63da35 100644
--- a/doc/examples/Makefile.am
+++ b/doc/examples/Makefile.am
@@ -1,6 +1,7 @@
## Process this file with automake to produce Makefile.in
-EXFILES = archive1.cpp compile1.cpp compile2.cpp compile3.cpp lanczos.cpp
+EXFILES = archive1.cpp compile1.cpp compile2.cpp compile3.cpp lanczos.cpp \
+ mystring.cpp
TEXI = ginac-examples.texi
diff --git a/doc/examples/mystring.cpp b/doc/examples/mystring.cpp
new file mode 100644
index 0000000..cf0d8a2
--- /dev/null
+++ b/doc/examples/mystring.cpp
@@ -0,0 +1,104 @@
+/**
+ * @file mystring.cpp Example of extending GiNaC: writing new classes
+ */
+#include <iostream>
+#include <string>
+#include <stdexcept>
+using namespace std;
+
+#include <ginac/ginac.h>
+using namespace GiNaC;
+
+class mystring : public basic
+{
+ GINAC_DECLARE_REGISTERED_CLASS(mystring, basic)
+
+public:
+ mystring(const string &s);
+ mystring(const char *s);
+ ex eval(int level) const;
+
+private:
+ string str;
+
+protected:
+ void do_print(const print_context &c, unsigned level = 0) const;
+
+};
+
+GINAC_IMPLEMENT_REGISTERED_CLASS_OPT(mystring, basic,
+ print_func<print_context>(&mystring::do_print))
+
+// ctors
+mystring::mystring() : inherited(&mystring::tinfo_static) { }
+mystring::mystring(const string &s) : inherited(&mystring::tinfo_static), str(s) { }
+mystring::mystring(const char *s) : inherited(&mystring::tinfo_static), str(s) { }
+
+// comparison
+int mystring::compare_same_type(const basic &other) const
+{
+ const mystring &o = static_cast<const mystring &>(other);
+ int cmpval = str.compare(o.str);
+ if (cmpval == 0)
+ return 0;
+ else if (cmpval < 0)
+ return -1;
+ else
+ return 1;
+}
+
+// archiving/unarchiving
+mystring::mystring(const archive_node &n, lst &sym_lst) : inherited(n, sym_lst)
+{
+ n.find_string("string", str);
+}
+
+void mystring::archive(archive_node &n) const
+{
+ inherited::archive(n);
+ n.add_string("string", str);
+}
+
+ex mystring::unarchive(const archive_node &n, lst &sym_lst)
+{
+ return (new mystring(n, sym_lst))->setflag(status_flags::dynallocated);
+}
+
+// printing
+void mystring::do_print(const print_context &c, unsigned level) const
+{
+ // print_context::s is a reference to an ostream
+ c.s << '\"' << str << '\"';
+}
+
+/**
+ * evaluation: all strings automatically converted to lowercase with
+ * non-alphabetic characters stripped, and empty strings removed
+ */
+ex mystring::eval(int level) const
+{
+ string new_str;
+ for (size_t i=0; i<str.length(); i++) {
+ char c = str[i];
+ if (c >= 'A' && c <= 'Z')
+ new_str += tolower(c);
+ else if (c >= 'a' && c <= 'z')
+ new_str += c;
+ }
+
+ if (new_str.length() == 0)
+ return 0;
+ else
+ return mystring(new_str).hold();
+}
+
+int main(int argc, char** argv)
+{
+ ex e = mystring("Hello, world!");
+ cout << is_a<mystring>(e) << endl;
+ cout << ex_to<basic>(e).class_name() << endl;
+ cout << e << endl;
+ ex another = pow(mystring("One string"), 2*sin(Pi-mystring("Another string")));
+ cout << another << endl;
+ return 0;
+}
diff --git a/doc/tutorial/ginac.texi b/doc/tutorial/ginac.texi
index a6befad..b2038db 100644
--- a/doc/tutorial/ginac.texi
+++ b/doc/tutorial/ginac.texi
@@ -7823,7 +7823,8 @@ Now we will start implementing a new class @code{mystring} that allows
placing character strings in algebraic expressions (this is not very useful,
but it's just an example). This class will be a direct subclass of
@code{basic}. You can use this sample implementation as a starting point
-for your own classes.
+for your own classes @footnote{The self-contained source for this example is
+included in GiNaC, see the @file{doc/examples/mystring.cpp} file.}.
The code snippets given here assume that you have included some header files
as follows:
--
1.4.4.4
Best regards,
Alexei
--
All science is either physics or stamp collecting.
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