Re: how to get an object instance from its class name?
dotNeter wrote:
On Mar 14, 4:51 pm, Michael DOUBEZ <michael.dou...@free.fr> wrote:
dotNeter a ?crit :
Is there any way for this?
If I get a string representing a class name, how do I new an instance
upon this name?
There is no native way. You have to use a factory i.e. an object that
knows how to build an object from a parameter. That also means that all
such object have a common ancestor.
There are many way to implement such a factory (builder, prototype ...).
But you have to know the types in advance or have a way to register
them into the factory.
An alternative non-portable way is to put those classes in a dynamic
library and define for each a factory function (make_<Class>() by
example) and then use the dlopen(), dlsym() calls to open the library
and call the factory function.
Michael
This is very fascinating. I've spent some time on factory pattern, but
I don't like to write so many switch-case in my system.
One further question is that if it truly fit my future requirement
since the classes may get enriched someday.
Don't use a switch-case. Use a std::map.
E.g.:
class base { };
class derived1 : public base { };
class derived2 : public base { };
....
class derivedn : public base { };
typedef base (*createfunc )(/*params if needed*/);
std::map<std::string, createfunc> factory_map;
then look up in the map instead of using a case statement.
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