doc/v622/vo001__AdoptOrOwnMemory_8py.html

import ROOT


# We use this class for didactic purposes: upon copy, a line is printed to the terminal.


ROOT.gInterpreter.Declare('''

class UponCopyPrinter {

public:

   UponCopyPrinter() = default;

   UponCopyPrinter(UponCopyPrinter &&) = default;

   UponCopyPrinter(const UponCopyPrinter &) { std::cout << "Invoking copy c'tor!" << std::endl; }

};

''')


RVec_UponCopyPrinter = ROOT.ROOT.VecOps.RVec(ROOT.UponCopyPrinter)


# One of the essential features of RVec is its ability of adopting and owning memory.

# Internally this is handled by the ROOT::Detail::VecOps::RAdoptAllocator class.


# Let's create an RVec of UponCopyPrinter instances. We expect no printout:

v = RVec_UponCopyPrinter(3)


# Let's adopt the memory from v into v2. We expect no printout:

v2 = RVec_UponCopyPrinter(v.data(), v.size())


# OK, let's check the addresses of the memory associated to the two RVecs It is the same!

print("%s and %s" %(v.data(), v2.data()))


# Now, upon reallocation, the RVec stops adopting the memory and starts owning it. And yes,

# a copy is triggered. Indeed internally the storage of the RVec is an std::vector. Moreover,

# the interface of the RVec is very, very similar to the one of std::vector: you have already

# noticed it when the `data()` method was invoked, right?

v2.resize(4)


# Of course, now the addresses are different.

print("%s and %s" %(v.data(), v2.data()))