[core] Make enum ↔ string conversion more generic-friendly

Rewrite enum.hpp in such a way that parseConstant can be defined generically for all enumerated types.

While there, properly validated enumerated property values.

1 files changed, 22 insertions, 38 deletions

diff --git a/include/mbgl/util/enum.hpp b/include/mbgl/util/enum.hpp
index 3fbf313aed..48ffda463e 100644
--- a/include/mbgl/util/enum.hpp
+++ b/include/mbgl/util/enum.hpp
@@ -1,52 +1,36 @@
 #pragma once
 
-#include <iosfwd>
+#include <mbgl/util/optional.hpp>
+
+#include <algorithm>
+#include <cassert>
 #include <string>
 
 namespace mbgl {
 
-template <typename Type>
-struct EnumValue {
-    const Type value;
-    const char *name;
-};
-
-template <typename EnumName, const EnumValue<EnumName> *names, const size_t length>
-struct Enum {
-    using Type = EnumName;
-    Type value;
-    static const constexpr size_t l = length;
-private:
-    static constexpr inline bool compare(const char *a, const char *b) {
-        return *a == *b && (*a == '\0' || compare(a + 1, b + 1));
-    }
-    static constexpr inline const char *lookup_type(Type e, EnumValue<Type> const * const list, size_t r) {
-        return r == 0 ? "" : list->value == e ? list->name : lookup_type(e, list + 1, r - 1);
-    }
-    static constexpr inline Type lookup_name(const char *n, EnumValue<Type> const * const list, size_t r) {
-        return r == 0 ? Type(-1) : compare(list->name, n) ? list->value : lookup_name(n, list + 1, r - 1);
-    }
+template <typename T>
+class Enum {
 public:
-    inline constexpr Enum(const char *n) : value(lookup_name(n, names, length)) {}
-    inline constexpr Enum(const std::string &n) : value(lookup_name(n.c_str(), names, length)) {}
-    inline constexpr Enum(Type t) : value(t) {}
-
-    inline void operator=(const char *n) { value = lookup_name(n, names, length); }
-    inline void operator=(const std::string &n) { *this = n.c_str(); }
-    inline void operator=(Type t) { value = t; }
+    using Value = std::pair<const T, const char *>;
 
-    inline constexpr bool valid() const { return value != Type(-1); }
+    static const char * toString(T t) {
+        auto it = std::find_if(begin, end, [&] (const auto& v) { return t == v.first; });
+        assert(it != end); return it->second;
+    }
 
-    inline constexpr const char *c_str() const { return lookup_type(value, names, length); }
-    inline std::string str() const { return c_str(); }
+    static optional<T> toEnum(const std::string& s) {
+        auto it = std::find_if(begin, end, [&] (const auto& v) { return s == v.second; });
+        return it == end ? optional<T>() : it->first;
+    }
 
-    inline constexpr operator Type() const { return value; }
+private:
+    static const Value* begin;
+    static const Value* end;
 };
 
-#define MBGL_DEFINE_ENUM_CLASS(name, type, strings...) \
-    const constexpr ::mbgl::EnumValue<type> type##_names[] = strings; \
-    using name = ::mbgl::Enum<type, type##_names, sizeof(type##_names) / sizeof(::mbgl::EnumValue<type>)>; \
-    inline std::ostream& operator<<(std::ostream& os, type t) { return os << name(t).str(); }
+#define MBGL_DEFINE_ENUM(type, strings...) \
+const constexpr Enum<type>::Value type##_names[] = strings; \
+template <> const Enum<type>::Value* Enum<type>::begin = std::begin(type##_names); \
+template <> const Enum<type>::Value* Enum<type>::end = std::end(type##_names)
 
 } // namespace mbgl
-