Hello,
My colleague came to find that, when defining a function that takes a const reference in C++ source code, “const T&” and “T const&” makes a difference when calling this function in PyROOT.
Here’s my example header file (forgive me to have a function implementation in the header… sorry)
#ifndef EMPTY_H
#define EMPTY_H
#include <iostream>
#include <TVector3.h>
class empty{
public:
empty(){}
virtual ~empty(){}
void f1(TVector3 v) { std::cout<<v.x()<<std::endl; }
void f2(const TVector3 v) { std::cout<<v.x()<<std::endl; }
void f3(const TVector3& v) { std::cout<<v.x()<<std::endl; }
void f4(TVector3 const& v) { std::cout<<v.x()<<std::endl; }
};
#endifHere’s my LinkDef.h
#ifdef __CINT__
#pragma link off all globals;
#pragma link off all classes;
#pragma link off all functions;
#pragma link C++ class empty+;
#endifHere’s a test python script:
from ROOT import TVector3,empty;
e=empty()
v=TVector3(0,0,0)
e.f1(v)
e.f2(v)
e.f3(v)
e.f4(v)Here’s an output:
0
0
0
Traceback (most recent call last):
File "try.py", line 9, in <module>
e.f4(v)
RuntimeError: could not resolve empty::f4(TVector3 const&)So it succeeds for empty::f3(const TVecotr3&) but it fails for empty::f4(TVector3 const&).
Is there a reason for this?
Now if I use std::vector in place of TVector3, both f4 succeeds.
Similarly, if I define my own custom class “foo”, this follows TVector3 observation: a function that takes “const foo&” succeeds, but a function that takes “foo const&” fails.
Thank you for your time in advance.
Best regards.
Kazu