Include <optional> from dedicated file optional.hpp

include/valijson/adapters/basic_adapter.hpp

@@ -5,16 +5,8 @@
 #include <stdint.h>
 #include <sstream>
 
-// This should be removed once C++17 is widely available
-#if __has_include(<optional>)
-#  include <optional>
-namespace opt = std;
-#else
-#  include <compat/optional.hpp>
-namespace opt = std::experimental;
-#endif
-
 #include <valijson/adapters/adapter.hpp>
+#include <valijson/internal/optional.hpp>
 
 namespace valijson {
 namespace adapters {

include/valijson/internal/json_pointer.hpp

@@ -9,15 +9,8 @@
 #include <stdexcept>
 #include <string>
 
-#if __has_include(<optional>)
-#  include <optional>
-namespace opt = std;
-#else
-#  include <compat/optional.hpp>
-namespace opt = std::experimental;
-#endif
-
 #include <valijson/adapters/adapter.hpp>
+#include <valijson/internal/optional.hpp>
 
 namespace valijson {
 namespace internal {

include/valijson/internal/json_reference.hpp

@@ -5,13 +5,7 @@
 #include <stdexcept>
 #include <string>
 
-#if __has_include(<optional>)
-#  include <optional>
-namespace opt = std;
-#else
-#  include <compat/optional.hpp>
-namespace opt = std::experimental;
-#endif
+#include <valijson/internal/optional.hpp>
 
 namespace valijson {
 namespace internal {

include/valijson/internal/optional.hpp

@@ -0,0 +1,14 @@
+#pragma once
+#ifndef __VALIJSON_OPTIONAL_HPP
+#define __VALIJSON_OPTIONAL_HPP
+
+// This should be removed once C++17 is widely available
+#if __has_include(<optional>)
+#  include <optional>
+namespace opt = std;
+#else
+#  include <compat/optional.hpp>
+namespace opt = std::experimental;
+#endif
+
+#endif

include/valijson/subschema.hpp

@@ -6,16 +6,8 @@
 
 #include <memory>
 
-// This should be removed once C++17 is widely available
-#if __has_include(<optional>)
-#  include <optional>
-namespace opt = std;
-#else
-#  include <compat/optional.hpp>
-namespace opt = std::experimental;
-#endif
-
 #include <valijson/constraints/constraint.hpp>
+#include <valijson/internal/optional.hpp>
 
 namespace valijson {