[C++-sig] Boost tuple example? (original) (raw)

David Abrahams dave at boost-consulting.com
Fri Dec 9 16:19:28 CET 2005

"Ralf W. Grosse-Kunstleve" <rwgk at yahoo.com> writes:

tuple Values("value 1", 2, 3.0); Does this work? I was thinking you need tuple Values = maketuple("value 1", 2, 3.0); but I am not sure.

Ralf is right.

try { I don't think it is advisable to use try + catch() here. Just let the exception propagate through to Python.

Ralf is right.

const char * szVal = extract<const char *>(oValues[0]); int nVal = extract(oValues[1]); double nDblVal = extract(oValues[2]); I believe this works on most compilers, but not all. I always do it like this: const char * szVal = extract<const char *>(oValues[0])(); I.e. with an additional "()" at the end. Similar for the two other extract<> statements.

Ralf, I'm really surprised. AFAIK the only compilers that need that syntax are vc6/7, which IIUC your code doesn't support.

} catch(...) { PyErrPrint(); } }

Does that seem reasonable? Also, is there an easy way to determine the length of a tuple in C++? David insisted on not giving us .size(), much to my dismay. Therefore you have to say: #include <boost/python/detail/apiplaceholder.hpp> and then: boost::python::len(obj) David: I still believe we should add .size() to tuple, list, str. The current solution is a real productivity killer; you won't believe how much time I spent/wasted over the years digging out that silly include above again and again. Purity is not always a virtue.

You could go ahead and add it, but it's not going to work on boost::python::object (unless you add it there, which is really impure!)

Wouldn't it be better just to make a single len function available in the same namespace as boost::python::object, and in the same header, so you can

len(obj)

without qualification? Seems more natural and broadly applicable to me.

-- Dave Abrahams Boost Consulting www.boost-consulting.com

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