From 457bfc2401028a9eb42b738401935d3ad1e1d984 Mon Sep 17 00:00:00 2001
From: Niels <niels.lohmann@gmail.com>
Date: Sun, 20 Dec 2015 15:30:07 +0100
Subject: [PATCH] work on #144

---
 README.md         |  2 +-
 src/json.hpp      |  6 +++++-
 src/json.hpp.re2c |  6 +++++-
 test/unit.cpp     | 13 +++++++++++++
 4 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/README.md b/README.md
index cd9be0d32..b671f3571 100644
--- a/README.md
+++ b/README.md
@@ -398,7 +398,7 @@ $ make
 $ ./json_unit "*"
 
 ===============================================================================
-All tests passed (3341846 assertions in 28 test cases)
+All tests passed (3341848 assertions in 28 test cases)
 ```
 
 For more information, have a look at the file [.travis.yml](https://github.com/nlohmann/json/blob/master/.travis.yml).
diff --git a/src/json.hpp b/src/json.hpp
index 9de73ddf1..6bfb44bff 100644
--- a/src/json.hpp
+++ b/src/json.hpp
@@ -2550,7 +2550,9 @@ class basic_json
 
     @tparam ValueType non-pointer type compatible to the JSON value, for
     instance `int` for JSON integer numbers, `bool` for JSON booleans, or
-    `std::vector` types for JSON arrays
+    `std::vector` types for JSON arrays. The character type of @ref string_t
+    as well as an initializer list of this type is excluded to avoid
+    ambiguities as these types implicitly convert to `std::string`.
 
     @return copy of the JSON value, converted to type @a ValueType
 
@@ -2571,6 +2573,8 @@ class basic_json
     template<typename ValueType, typename
              std::enable_if<
                  not std::is_pointer<ValueType>::value
+                 and not std::is_same<ValueType, typename string_t::value_type>::value
+                 and not std::is_same<ValueType, std::initializer_list<typename string_t::value_type>>::value
                  , int>::type = 0>
     operator ValueType() const
     {
diff --git a/src/json.hpp.re2c b/src/json.hpp.re2c
index 5cee92f4b..3ab1dfce1 100644
--- a/src/json.hpp.re2c
+++ b/src/json.hpp.re2c
@@ -2550,7 +2550,9 @@ class basic_json
 
     @tparam ValueType non-pointer type compatible to the JSON value, for
     instance `int` for JSON integer numbers, `bool` for JSON booleans, or
-    `std::vector` types for JSON arrays
+    `std::vector` types for JSON arrays. The character type of @ref string_t
+    as well as an initializer list of this type is excluded to avoid
+    ambiguities as these types implicitly convert to `std::string`.
 
     @return copy of the JSON value, converted to type @a ValueType
 
@@ -2571,6 +2573,8 @@ class basic_json
     template<typename ValueType, typename
              std::enable_if<
                  not std::is_pointer<ValueType>::value
+                 and not std::is_same<ValueType, typename string_t::value_type>::value
+                 and not std::is_same<ValueType, std::initializer_list<typename string_t::value_type>>::value
                  , int>::type = 0>
     operator ValueType() const
     {
diff --git a/test/unit.cpp b/test/unit.cpp
index 8826d835e..b143f31b5 100644
--- a/test/unit.cpp
+++ b/test/unit.cpp
@@ -10323,6 +10323,19 @@ TEST_CASE("regression tests")
         CHECK(j["string"] == "\u0007\u0007");
     }
 
+    SECTION("issue #144 - implicit assignment to std::string fails")
+    {
+        json o = {{"name", "value"}};
+
+        std::string s1 = o["name"];
+        CHECK(s1 == "value");
+
+        std::string s2;
+        s2 = o["name"];
+
+        CHECK(s2 == "value");
+    }
+
     SECTION("character following a surrogate pair is skipped")
     {
         CHECK(json::parse("\"\\ud80c\\udc60abc\"").get<json::string_t>() == u8"\U00013060abc");
-- 
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