From 9f64feed0cf9e364b7282fbd1d11325305d70754 Mon Sep 17 00:00:00 2001
From: greg <greg7mdp@gmail.com>
Date: Sat, 28 Mar 2020 17:46:47 -0400
Subject: [PATCH] fix compilation issue with string_view

---
 parallel_hashmap/phmap_config.h | 7 +++++--
 parallel_hashmap/phmap_utils.h  | 2 +-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/parallel_hashmap/phmap_config.h b/parallel_hashmap/phmap_config.h
index 49a14ce..dd5a0bf 100644
--- a/parallel_hashmap/phmap_config.h
+++ b/parallel_hashmap/phmap_config.h
@@ -296,7 +296,8 @@
 #endif
 
 #ifdef __has_include
-    #if __has_include(<string_view>) && __cplusplus >= 201703L
+    #if __has_include(<string_view>) && __cplusplus >= 201703L && \
+        (!defined(_MSC_VER) || _MSC_VER >= 1920) // vs2019
         #define PHMAP_HAVE_STD_STRING_VIEW 1
     #endif
 #endif
@@ -308,7 +309,9 @@
     // #define PHMAP_HAVE_STD_ANY 1
     #define PHMAP_HAVE_STD_OPTIONAL 1
     #define PHMAP_HAVE_STD_VARIANT 1
-    #define PHMAP_HAVE_STD_STRING_VIEW 1
+    #if !defined(PHMAP_HAVE_STD_STRING_VIEW) && _MSC_VER >= 1920
+        #define PHMAP_HAVE_STD_STRING_VIEW 1
+    #endif
 #endif
 
 #if (defined(_MSVC_LANG) && _MSVC_LANG >= 201703) || __cplusplus >= 201703
diff --git a/parallel_hashmap/phmap_utils.h b/parallel_hashmap/phmap_utils.h
index 76818f2..0f38efa 100644
--- a/parallel_hashmap/phmap_utils.h
+++ b/parallel_hashmap/phmap_utils.h
@@ -123,7 +123,7 @@ private:
     typedef std::true_type yes;
     typedef std::false_type no;
 
-    template<typename U> static auto test(int) -> decltype(hash_value(std::declval<U&>()) == 1, yes());
+    template<typename U> static auto test(int) -> decltype(hash_value(std::declval<const U&>()) == 1, yes());
 
     template<typename> static no test(...);