Std::shared_ptr::reset in PyROOT

[oxon]

---

ROOT Version: 6.16.00
Platform: macOS 10.14
Compiler: Clang 10.0.1

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How do I access std::shared_ptr::reset in PyROOT?

In [1]: import ROOT                                                             

In [2]: ROOT.gROOT.ProcessLine('std::shared_ptr<TCanvas> can;')                 
Out[2]: 4550143272

In [3]: ROOT.can.reset                                                          
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-4-7cd261822618> in <module>
----> 1 ROOT.can.reset

AttributeError: 'TCanvas' object has no attribute 'reset'

[etejedor]

Hi @oxon ,

You can do:

ROOT.can.__smartptr__().reset()

Cheers,
Enric

[oxon]

Thank you. As I could not find __smartptr__, I tried using _get_smart_ptr instead. But I could not reset the pointer because of a template issue. Could you please tell me how to fix it again?

In [2]: import ROOT                                                                                         

In [3]: ROOT.gROOT.ProcessLine('std::shared_ptr<TCanvas> can(new TCanvas());')                              
Out[3]: 4431397272

In [5]: ROOT.can.__smartptr__()                                                                                    
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-5-e56709dfe148> in <module>
----> 1 c.__smartptr__()

AttributeError: 'TCanvas' object has no attribute '__smartptr__'

In [7]: ROOT.can._get_smart_ptr()                                                                           
Out[7]: <ROOT.shared_ptr<TCanvas> object at 0x10821c198>

In [8]: ROOT.can._get_smart_ptr().reset                                                                     
Out[8]: <ROOT.TemplateProxy at 0x11cc70ef8>

In [9]: ROOT.can._get_smart_ptr().reset(ROOT.TCanvas())                                                     
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-9-92b0cbd81331> in <module>
----> 1 ROOT.can._get_smart_ptr().reset(ROOT.TCanvas())

TypeError: can not resolve method template call for 'reset'

[etejedor]

Hi,

That looks like a bug in the template proxy. I created an issue for it:

https://sft.its.cern.ch/jira/browse/ROOT-10245

In the meantime, just like you create the smart pointer in C++ with ProcessLine, you could also reset its value via the same mechanism.

Cheers,
Enric

[oxon]

Thanks a lot. ProcessLine works, and it is good enough for the moment.

[wlav]

Just for fun, the current state of smart ptr’s in cppyy can now create them from python classes derived from (abstract) C++ ones and take care of all the memory handling, see below. Soon enough things like reset() will not be needed anymore.

import cppyy

cppyy.cppdef("""
class AbstractCommand {
public:
    virtual ~AbstractCommand() { std::cerr << "command destroyed " << std::endl; }
    virtual int run() = 0;
};

int run_command(std::shared_ptr<AbstractCommand> ptr) {
    return ptr->run();
}
""")

from cppyy.interactive import *

class PyCommand(AbstractCommand):
    def __init__(self, val):
        super(PyCommand, self).__init__()
        self.val = val

    def run(self):
         print("Running PyCommand ...")
         return self.val

v = std.make_shared[PyCommand](42)

print(run_command(v))
del v
print('done')

which outputs:

Running PyCommand ...
42
command destroyed 
done