# C++ keyword: reflexpr (reflection TS)

From cppreference.com
< cpp‎ | keyword

### Usage

1) Gets the member list of a class type, or the enumerator list of an enum type.
2) Gets the name of type and member.
3) Detects whether a data member is static or constexpr.
4) Detects whether member function is virtual, public, protected or private.
5) Get the row and column of the source code when the type defines.

### Example

`reflexpr` provides us the meta info of the object via meta-object types. Note that `std::reflect::get_data_members_t` make programmers able to visit any class just like std::tuple.

Run this code

    #include <string>
    #include <vector>

    struct S
    {
        int b;
        std::string s;
        std::vector<std::string> v;
    };

    // Reflection TS
    #include <experimental/reflect>
    using meta_S = reflexpr(S);
    using mem = std::reflect::get_data_members_t<meta_S>;
    using meta = std::reflect::get_data_members_t<mem>;
    static_assert(std::reflect::is_public_v<meta>); // successful

    int main() {}

We can also know the name info from `reflexpr`:

Run this code

    #include <iostream>
    #include <string>
    #include <string_view>
    // Reflection TS
    #include <experimental/reflect>

    template<typename Tp>
    constexpr std::string_view nameof()
    {
        using TpInfo = reflexpr(Tp);
        using aliased_Info = std::experimental::reflect::get_aliased_t<TpInfo>;
        return std::experimental::reflect::get_name_v<aliased_Info>;
    }

    int main()
    {
        std::cout << nameof<std::string>() << '\n';
        static_assert(nameof<std::string>() == "basic_string"); // successful
    }

This is an example of getting the scope of a type in the Reflection TS.

Run this code

    namespace Foo
    {
        struct FooFoo
        {
            int FooFooFoo;
        };
    }
    namespace Bar
    {
        using BarBar = ::Foo::FooFoo;
    }
    using BarBarInfo = reflexpr(::Bar::BarBar);
    using BarBarScope = ::std::experimental::reflect::get_scope_t<BarBarInfo>; // Bar, not Foo

    struct Spam
    {
        int SpamSpam;
    };
    struct Grok
    {
        using GrokGrok = Spam::SpamSpam;
    };
    using GrokGrokInfo = reflexpr(::Grok::GrokGrok);
    using GrokGrokScope = std::experimental::reflect::get_scope_t<GrokGrokInfo>; // Grok, not Spam

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/keyword/reflexpr&oldid=151633"