Let's say I have a std::any
object which may or may not contain a pointer to some derived class of a given base class B
. Is there any way I can do something that:
B *
, if the std::any
object holds something convertible to B *
, orIt seems like dynamic_cast
and std::any_cast
each provide one half of this functionality, but I don't see any way of putting the two together.
I'm aware that I can make this work in various ways that involve explicitly enumerating every type convertible to B *
, but that's the mother of all DRY violations.
Sample use case:
std::vector<std::any> setupTools(const std::string & confFile)
{
std::vector<std::any> myTools;
auto conf = parse(confFile);
for(std::string & wrenchInfo : conf["Wrenches"])
{
Wrench::setup(myTools, wrenchInfo);
}
for(std::string & hammerInfo : conf["Hammers"])
{
Hammer::setup(myTools, hammerInfo);
}
// 25 more kinds of tools
}
Factory1::init(const std::vector<std::any> & tools)
{
m_wrench = any_get<Wrench *>(tools);
m_hammer = any_get<Hammer *>(tools);
m_saw = any_get<Saw *>(tools);
}
Factory2::init(const std::vector<std::any> & tools)
{
m_wrench = any_get<TorqueWrench *>(tools);
}
Factory3::init(const std::vector<std::any> & tools)
{
m_saw = any_get<CordlessReciprocatingSaw *>(tools);
}
I don't want to include a bunch of boilerplate code listing every single kind of saw in existence just so I can grab a saw -- any Saw
-- to use in Factory1
.
This is unachievable. It is only possible to get an object out from std::any
using exactly the type that was put inside. Thus, you must know the type to get anything out of it.
It seems that std::any
does not fit your use case.