CODEWITHSUNDEEP
c++c++11templates
InContext
InContext

Reputation: 2501

C++ 11 template sub type

With more detail added

I'm looking to inject in a type and use this as the template type, in addition to this I would like to implicitly pass in a subtype to be used.

Implementation:

MyClass<MyTestClass> myClass;

const auto& testDataReturn = myClass.m_typeObject.m_field1;

// looking to be able to call myClass.m_subTypeObject here which is implicitly typed from the parent type (see template def below)

Template:

template<class T>
class MyClass
{
public:

    T m_typeObject;
    typename T::SubType m_subTypeObject; // **does not like this**
};

typedef MyType SubType;

Class definitions:

class SubTypeImpl
{
public:
    std::string m_field1 = "test1Sub";
    std::string m_field2 = "test2Sub";
};

class MyTestClass
{

public:
    std::string m_field1 = "test1";
    SubTypeImpl SubType;
};

Upvotes: 1

Views: 423

Answers (2)

diametralpitch
diametralpitch

Reputation: 685

I may not fully understand the question, but it seems if you change

SubTypeImpl SubType;

to

typedef SubTypeImpl SubType;

you can achieve what you want.

Upvotes: 1

Yakk - Adam Nevraumont
Yakk - Adam Nevraumont

Reputation: 275340

T::SubType is not a type, it is a member field.

template<class T>
using SubType = decltype(std::declval<T&>().SubType);

that gets the type of the SubType member of T, assuming it is public.

template<class T>
class MyClass {
public:

  T m_typeObject;
  SubType<T> m_subTypeObject;
};

you could do the decltype inline in the MyClass definition, but that is messy.

Upvotes: 2

Related Questions