Why I cannot store abstract class in map by const reference?

Asked Oct 07 '16 at 15:09

Active Oct 07 '16 at 15:15

Viewed 71 times

I have some base abstract class A like that:

class A
{
  public:
     virtual void foo() = 0;
};

I want to use following map:

 std::map<std::string, const A&> some_map;

But compiler tells that Code declares an instance of an abstract class or structure. It seems for me weird

EDIT: following type works fine:

std::map<std::string, const A*> some_map;

edited Oct 07 '16 at 15:15

asked Oct 07 '16 at 15:09

Alex Aparin

2

Have a look at this: http://en.cppreference.com/w/cpp/utility/functional/reference_wrapper – Bathsheba Oct 07 '16 at 15:11
Neither clang nor gcc forbid me from creating `map` and using it (except for the obviously impossible code like default-initialized references or reassigning them) – krzaq Oct 07 '16 at 15:18
The code compiles fine using g++6. What compiler did you use? – Donghui Zhang Oct 07 '16 at 15:18
@Donghui Zhang, i am using msvc2015 studio with its compiler – Alex Aparin Oct 07 '16 at 15:19
1

@krzaq You can't do it anyways, it's not legal. – Baum mit Augen Oct 07 '16 at 15:24
Well, it seems to be Visual Studio specific then. I guess if you continue to use Visual Studio, you'll have to use a workaround such as storing a pointer instead of a reference. – Donghui Zhang Oct 07 '16 at 15:24
@DonghuiZhang Just because gcc does not give you a diagnostic does not mean the code is correct. It is not, independent of the compiler in use. – Baum mit Augen Oct 07 '16 at 15:27
@BaummitAugen I didn't see anything to this effect in container requirements. Would you mind pointing me in the right direction? – krzaq Oct 07 '16 at 15:27
1

@krzaq See the dupe. – Baum mit Augen Oct 07 '16 at 15:28
@BaummitAugen thanks, it's clear now :) – krzaq Oct 07 '16 at 15:29

0 Answers0