Passing child class objects to std::function parameter
I have the following message class psuedo-code (third-party, cannot be changed).
messages.h:
class AbstractMessage {
// pure virtual
};
class MessageA : public AbstractMessage {
// implements everything
const static std::string messageName = "MessageA";
};
class MessageB : public AbstractMessage {
// implements everything
const static std::string messageName = "MessageB";
};
In my application code, I am attempting to write a function to register an external function to handle any message:
application.cpp:
bool register_handler(std::string messageType, std::function<void(AbstractMessage&)>messageHandler) {
// add the string and function to a map to be called
}
However, I need to be able to pass in MessageA or MessageB functions. For example:
main.cpp:
void processMessageA(MessageA &msg) {
// do something
}
Application myApp;
This becomes problematic when I attempt to do the following:
std::function<void(MessageA&)> f(processMessageA);
myApp.register_handler("MessageA", f);
MessageA should be a valid AbstractMessage via inheritance, but I get the following error:
'Error C2664: 'bool Application::register_handler(std::string,const std::function<void (AbstractMessage &)> &)': cannot convert argument 2 from 'std::function<void(MessageA &)>' to 'const std::function<void (AbstractMessage &)> &
Is this possible in C++? In Java I would use a functional interface, and pass any valid method via this::. Inheritance would validate the method parameters.
c++ function inheritance stl
asked Nov 26 '18 at 22:39
AlanAlan
269520
add a comment |
I have the following message class psuedo-code (third-party, cannot be changed).
messages.h:
class AbstractMessage {
// pure virtual
};
class MessageA : public AbstractMessage {
// implements everything
const static std::string messageName = "MessageA";
};
class MessageB : public AbstractMessage {
// implements everything
const static std::string messageName = "MessageB";
};
In my application code, I am attempting to write a function to register an external function to handle any message:
application.cpp:
bool register_handler(std::string messageType, std::function<void(AbstractMessage&)>messageHandler) {
// add the string and function to a map to be called
}
However, I need to be able to pass in MessageA or MessageB functions. For example:
main.cpp:
void processMessageA(MessageA &msg) {
// do something
}
Application myApp;
This becomes problematic when I attempt to do the following:
std::function<void(MessageA&)> f(processMessageA);
myApp.register_handler("MessageA", f);
MessageA should be a valid AbstractMessage via inheritance, but I get the following error:
'Error C2664: 'bool Application::register_handler(std::string,const std::function<void (AbstractMessage &)> &)': cannot convert argument 2 from 'std::function<void(MessageA &)>' to 'const std::function<void (AbstractMessage &)> &
Is this possible in C++? In Java I would use a functional interface, and pass any valid method via this::. Inheritance would validate the method parameters.
c++ function inheritance stl
asked Nov 26 '18 at 22:39
AlanAlan
269520
Let's say you manage to cast yourvoid(MessageA&)to avoid(AbstractMessage&). What happens when you pass in aMessageBto that function?
– super
Nov 26 '18 at 23:23
@super I‘m following. What would be the alternative or best practice for generic message handler mapping? I tried using a template, but had issues using it as a map key to determine which handler to call.
– Alan
Nov 26 '18 at 23:37
A better design would not need to know the exact type, the interface (AbstractMessage&) should be enough. But if you third party code is preventing that, casting is your only option AFAIK.
– super
Nov 26 '18 at 23:46
@super Now I’m not following, my current scenario is I have the interface AbstractMessage&.
– Alan
Nov 27 '18 at 0:10
add a comment |
I have the following message class psuedo-code (third-party, cannot be changed).
messages.h:
class AbstractMessage {
// pure virtual
};
class MessageA : public AbstractMessage {
// implements everything
const static std::string messageName = "MessageA";
};
class MessageB : public AbstractMessage {
// implements everything
const static std::string messageName = "MessageB";
};
In my application code, I am attempting to write a function to register an external function to handle any message:
application.cpp:
bool register_handler(std::string messageType, std::function<void(AbstractMessage&)>messageHandler) {
// add the string and function to a map to be called
}
However, I need to be able to pass in MessageA or MessageB functions. For example:
main.cpp:
void processMessageA(MessageA &msg) {
// do something
}
Application myApp;
This becomes problematic when I attempt to do the following:
std::function<void(MessageA&)> f(processMessageA);
myApp.register_handler("MessageA", f);
MessageA should be a valid AbstractMessage via inheritance, but I get the following error:
'Error C2664: 'bool Application::register_handler(std::string,const std::function<void (AbstractMessage &)> &)': cannot convert argument 2 from 'std::function<void(MessageA &)>' to 'const std::function<void (AbstractMessage &)> &
Is this possible in C++? In Java I would use a functional interface, and pass any valid method via this::. Inheritance would validate the method parameters.
c++ function inheritance stl
asked Nov 26 '18 at 22:39
AlanAlan
269520
I have the following message class psuedo-code (third-party, cannot be changed).
messages.h:
class AbstractMessage {
// pure virtual
};
class MessageA : public AbstractMessage {
// implements everything
const static std::string messageName = "MessageA";
};
class MessageB : public AbstractMessage {
// implements everything
const static std::string messageName = "MessageB";
};
In my application code, I am attempting to write a function to register an external function to handle any message:
application.cpp:
bool register_handler(std::string messageType, std::function<void(AbstractMessage&)>messageHandler) {
// add the string and function to a map to be called
}
However, I need to be able to pass in MessageA or MessageB functions. For example:
main.cpp:
void processMessageA(MessageA &msg) {
// do something
}
Application myApp;
This becomes problematic when I attempt to do the following:
std::function<void(MessageA&)> f(processMessageA);
myApp.register_handler("MessageA", f);
MessageA should be a valid AbstractMessage via inheritance, but I get the following error:
'Error C2664: 'bool Application::register_handler(std::string,const std::function<void (AbstractMessage &)> &)': cannot convert argument 2 from 'std::function<void(MessageA &)>' to 'const std::function<void (AbstractMessage &)> &
Is this possible in C++? In Java I would use a functional interface, and pass any valid method via this::. Inheritance would validate the method parameters.
c++ function inheritance stl
c++ function inheritance stl
asked Nov 26 '18 at 22:39
AlanAlan
269520
asked Nov 26 '18 at 22:39
AlanAlan
269520
asked Nov 26 '18 at 22:39
AlanAlan
269520
asked Nov 26 '18 at 22:39
AlanAlan
269520
asked Nov 26 '18 at 22:39
AlanAlan
269520
269520
Let's say you manage to cast yourvoid(MessageA&)to avoid(AbstractMessage&). What happens when you pass in aMessageBto that function?
– super
Nov 26 '18 at 23:23
@super I‘m following. What would be the alternative or best practice for generic message handler mapping? I tried using a template, but had issues using it as a map key to determine which handler to call.
– Alan
Nov 26 '18 at 23:37
A better design would not need to know the exact type, the interface (AbstractMessage&) should be enough. But if you third party code is preventing that, casting is your only option AFAIK.
– super
Nov 26 '18 at 23:46
@super Now I’m not following, my current scenario is I have the interface AbstractMessage&.
– Alan
Nov 27 '18 at 0:10
add a comment |
Let's say you manage to cast yourvoid(MessageA&)to avoid(AbstractMessage&). What happens when you pass in aMessageBto that function?
– super
Nov 26 '18 at 23:23
@super I‘m following. What would be the alternative or best practice for generic message handler mapping? I tried using a template, but had issues using it as a map key to determine which handler to call.
– Alan
Nov 26 '18 at 23:37
A better design would not need to know the exact type, the interface (AbstractMessage&) should be enough. But if you third party code is preventing that, casting is your only option AFAIK.
– super
Nov 26 '18 at 23:46
@super Now I’m not following, my current scenario is I have the interface AbstractMessage&.
– Alan
Nov 27 '18 at 0:10
Let's say you manage to cast your
void(MessageA&) to a void(AbstractMessage&). What happens when you pass in a MessageB to that function?– super
Nov 26 '18 at 23:23
Let's say you manage to cast your
void(MessageA&) to a void(AbstractMessage&). What happens when you pass in a MessageB to that function?– super
Nov 26 '18 at 23:23
@super I‘m following. What would be the alternative or best practice for generic message handler mapping? I tried using a template, but had issues using it as a map key to determine which handler to call.
– Alan
Nov 26 '18 at 23:37
@super I‘m following. What would be the alternative or best practice for generic message handler mapping? I tried using a template, but had issues using it as a map key to determine which handler to call.
– Alan
Nov 26 '18 at 23:37
A better design would not need to know the exact type, the interface (
AbstractMessage&) should be enough. But if you third party code is preventing that, casting is your only option AFAIK.– super
Nov 26 '18 at 23:46
A better design would not need to know the exact type, the interface (
AbstractMessage&) should be enough. But if you third party code is preventing that, casting is your only option AFAIK.– super
Nov 26 '18 at 23:46
@super Now I’m not following, my current scenario is I have the interface AbstractMessage&.
– Alan
Nov 27 '18 at 0:10
@super Now I’m not following, my current scenario is I have the interface AbstractMessage&.
– Alan
Nov 27 '18 at 0:10
add a comment |
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Let's say you manage to cast your
void(MessageA&)to avoid(AbstractMessage&). What happens when you pass in aMessageBto that function?– super
Nov 26 '18 at 23:23
@super I‘m following. What would be the alternative or best practice for generic message handler mapping? I tried using a template, but had issues using it as a map key to determine which handler to call.
– Alan
Nov 26 '18 at 23:37
A better design would not need to know the exact type, the interface (
AbstractMessage&) should be enough. But if you third party code is preventing that, casting is your only option AFAIK.– super
Nov 26 '18 at 23:46
@super Now I’m not following, my current scenario is I have the interface AbstractMessage&.
– Alan
Nov 27 '18 at 0:10