[boost] [gsoc16] Can I quickly check if the below really is the best approach?

Subject: [boost] [gsoc16] Can I quickly check if the below really is the best approach?
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2016-01-12 15:09:02

Dear Boost,

In the prototype https://svn.boost.org/trac/boost/wiki/SoC2016 at 
https://goo.gl/1CQAuQ I claim "Even with all of Boost's facilities 
[1] and using C++ 14, this program represents the currently best 
available method of implementing a static constant associative map of 
keys to values" and you can find either the code at the link or 
pasted below.

Can I quickly check here if that claim is true? Is there a better way 
than my example program?

BTW by static constant associative map of keys to values I mean the 
thing me and Tony van Eerd were speaking about here last year and the 
year before, and indeed frequently at BlackBerry!

Niall

[1]: I believe Boost.Hana could implement a static constan 
associative map quite easily, but I'd be fairly sure Hana will likely 
be beyond most students.

--- cut ---
#include <initializer_list>
#include <experimental/string_view>
#include <map>
#include <unordered_map>
#include <iostream>

using std::experimental::string_view;

enum class weekday { sunday, monday, tuesday, wednesday, thursday, 
friday, saturday };

// initializer_list, pair and string_view are constexpr, so this list 
can be constexpr
// (i.e. lives in the mind of the compiler only and has zero 
representation in generated code)
#define STRING_VIEW(str) { str, sizeof(str)-1 }
constexpr std::initializer_list<std::pair<const string_view, 
weekday>> string_to_weekday {
    { STRING_VIEW("sunday"),    weekday::sunday },
    { STRING_VIEW("monday"),    weekday::monday },
    { STRING_VIEW("tuesday"),   weekday::tuesday },
    { STRING_VIEW("wednesday"), weekday::wednesday },
    { STRING_VIEW("thursday"),  weekday::thursday },
    { STRING_VIEW("friday"),    weekday::friday },
    { STRING_VIEW("saturday"),  weekday::saturday }
};

int main(void)
{
  {
    // Calls malloc() at least 7 times
    static const std::map<string_view, weekday> to_weekday1 = 
string_to_weekday;
    std::cout << "'monday' maps to " << 
static_cast<int>(to_weekday1.at("monday")) << std::endl;
    std::cout << "'friday' maps to " << 
static_cast<int>(to_weekday1.at("friday")) << std::endl;
    // Calls free() at least 7 times
  }
  {
    // Calls malloc() at least 8 times
    static const std::unordered_map<string_view, weekday> to_weekday2 
= string_to_weekday;
    std::cout << "'monday' maps to " << 
static_cast<int>(to_weekday2.at("monday")) << std::endl;
    std::cout << "'friday' maps to " << 
static_cast<int>(to_weekday2.at("friday")) << std::endl;
    // Calls free() at least 8 times
  }
  return 0;
}
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