How do I remove code duplication between similar const and non-const member functions?

Question

Let\'s say I have the following class X where I want to return access to an internal member:

class Z
{
    // details
};

class X
{
    std::vec         


        

Answer 1

For those (like me) who

• use c++17
• want to add the least amount of boilerplate/repetition and
• don't mind using macros (while waiting for meta-classes...),

here is another take:

#include 
#include 

template  struct NonConst;
template  struct NonConst {using type = T&;};
template  struct NonConst {using type = T*;};

#define NON_CONST(func)                                                     \
    template  auto func(T&&... a)                            \
        -> typename NonConst(a)...))>::type   \
    {                                                                       \
        return const_cast(a)...))>(           \
            std::as_const(*this).func(std::forward(a)...));              \
    }

It is basically a mix of the answers from @Pait, @DavidStone and @sh1 (EDIT: and an improvement from @cdhowie). What it adds to the table is that you get away with only one extra line of code which simply names the function (but no argument or return type duplication):

class X
{
    const Z& get(size_t index) const { ... }
    NON_CONST(get)
};

Note: gcc fails to compile this prior to 8.1, clang-5 and upwards as well as MSVC-19 are happy (according to the compiler explorer).