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cmkr/include/enum_helper.hpp

69 lines
2.1 KiB

// https://codereview.stackexchange.com/a/14315
#include <algorithm>
#include <iostream>
#include <sstream>
#include <string>
// This is the type that will hold all the strings.
// Each enumeration type will declare its own specialization.
// Any enum that does not have a specialization will generate a compiler error
// indicating that there is no definition of this variable (as there should be
// be no definition of a generic version).
template <typename T>
struct enumStrings {
static char const *data[];
};
// This is a utility type.
// Created automatically. Should not be used directly.
template <typename T>
struct enumRefHolder {
T &enumVal;
enumRefHolder(T &enumVal) : enumVal(enumVal) {}
};
template <typename T>
struct enumConstRefHolder {
T const &enumVal;
enumConstRefHolder(T const &enumVal) : enumVal(enumVal) {}
};
// The next two functions do the actual work of reading/writing an
// enum as a string.
template <typename T>
std::ostream &operator<<(std::ostream &str, enumConstRefHolder<T> const &data) {
return str << enumStrings<T>::data[data.enumVal];
}
template <typename T>
std::istream &operator>>(std::istream &str, enumRefHolder<T> const &data) {
std::string value;
str >> value;
// These two can be made easier to read in C++11
// using std::begin() and std::end()
//
static auto begin = std::begin(enumStrings<T>::data);
static auto end = std::end(enumStrings<T>::data);
auto find = std::find(begin, end, value);
if (find != end) {
data.enumVal = static_cast<T>(std::distance(begin, find));
} else {
throw std::invalid_argument("");
}
return str;
}
// This is the public interface:
// use the ability of function to deduce their template type without
// being explicitly told to create the correct type of enumRefHolder<T>
template <typename T>
enumConstRefHolder<T> enumToString(T const &e) {
return enumConstRefHolder<T>(e);
}
template <typename T>
enumRefHolder<T> enumFromString(T &e) {
return enumRefHolder<T>(e);
}