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Allow passing a derived object to a port requiring a base class #943
Description
Is your feature request related to a problem? Please describe.
There is a lot of boilerplate code needed for converting libraries, relying on inheritance, into BT nodes. Consider this example:
// Base class
class Greeter {
public:
virtual std::string show_msg() const = 0;
virtual ~Greeter() {}
};
// Derived class
class HelloGreeter : public Greeter {
public:
std::string show_msg() const override { return "hello"; }
void setDerivedParameter(int n);
};I have 2 options if I want to use a unique method from the derived class as well as store it's base class somewhere, e.g. inside a vector.
<!-- OPTION 1- return base and derived class -->
<CreateHelloGreeter out_derived="{hello_greeter}" out_base="{greeter}" />
<!-- OPTION 2- convert to base -->
<CreateHelloGreeter out_derived="{hello_greeter}" />
<UpcastHelloGreeter in={hello_greater} out_base="{greeter}" />
<setDerivedParameter in_derived="{hello_greater}" n="2" />
<VectorInsertGreeter in_base="{greeter}" />Describe the solution you'd like
I would like the ability to allow passing a derived object directly to a port requiring a base class.
<CreateHelloGreeter out_derived="{hello_greeter}" />
<setDerivedParameter in_derived="{hello_greater}" n="2" />
<InsertToGreeterVector in_base="{hello_greeter}" />As you see, this would reduce boilerplate code in the C++ and in the XML representation. Is there any way to reduce the strictness of the custom std::any used in this project to enable this feature ? I think that this project https://github.com/samee/any_of implements this behavior.
There is also the problem that BT evaluates ports type for consistency. I don't think one can deduce the base class of a derived class
typeid...
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facontidavide commentedon Mar 1, 2025
this is a good point.
Yes, I think it is safe to reduce the strictness of the any_cast.
Can you please help creating a PR with a unit test of the desired behavior, i.e. somehting like this should work out of the box
I am not sure if there is an easy fix for that, I need to investigate
Add polymorphic shared_ptr port support (Issue #943)
Add polymorphic shared_ptr port support (Issue #943)
Add polymorphic shared_ptr port support (Issue #943)
Add polymorphic shared_ptr port support (Issue #943)
Add polymorphic shared_ptr port support (Issue #943)
Add polymorphic shared_ptr port support (Issue #943) (#1107)
facontidavide commentedon Oct 24, 2026
Fixed by #1107 (1e166f5). Register the inheritance once with
factory.registerPolymorphicCast<Derived, Base>(), and astd::shared_ptr<Derived>output can then be read by astd::shared_ptr<Base>input port (seetests/gtest_polymorphic_ports.cpp). Making the cast automatic, without registration, would need a separate feature request.