Mark get_type_index() as deprecated.

See #73.

Author: joto

test/t/variant.cpp

@@ -279,7 +279,6 @@ TEST_CASE( "variant default constructor", "[variant][default constructor]" ) {
     using variant_type = mapbox::util::variant<int, double, std::string>;
     REQUIRE(variant_type{}.which() == 0);
     REQUIRE(variant_type{}.valid());
-    REQUIRE(variant_type{mapbox::util::no_init()}.get_type_index() == mapbox::util::detail::invalid_value);
     REQUIRE_FALSE(variant_type{mapbox::util::no_init()}.valid());
 }
 

variant.hpp

@@ -782,7 +782,9 @@ class variant
         }
     }
 
-    VARIANT_INLINE std::size_t get_type_index() const
+    // This function is deprecated because it returns an internal index field.
+    // Use which() instead.
+    VARIANT_INLINE MAPBOX_VARIANT_DEPRECATED std::size_t get_type_index() const
     {
         return type_index;
     }