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https://github.com/nlohmann/json
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✨ make emplace_back return a reference #1609
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@ -4952,6 +4952,8 @@ class basic_json
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@param[in] args arguments to forward to a constructor of @ref basic_json
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@tparam Args compatible types to create a @ref basic_json object
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@return reference to the inserted element
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@throw type_error.311 when called on a type other than JSON array or
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null; example: `"cannot use emplace_back() with number"`
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@ -4961,10 +4963,10 @@ class basic_json
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elements to a JSON array. Note how the `null` value was silently converted
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to a JSON array.,emplace_back}
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@since version 2.0.8
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@since version 2.0.8, returns reference since 3.7.0
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*/
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template<class... Args>
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void emplace_back(Args&& ... args)
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reference emplace_back(Args&& ... args)
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{
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// emplace_back only works for null objects or arrays
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if (JSON_UNLIKELY(not(is_null() or is_array())))
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@ -4981,7 +4983,12 @@ class basic_json
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}
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// add element to array (perfect forwarding)
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#ifdef JSON_HAS_CPP_17
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return m_value.array->emplace_back(std::forward<Args>(args)...);
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#else
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m_value.array->emplace_back(std::forward<Args>(args)...);
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return m_value.array->back();
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#endif
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}
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/*!
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@ -17763,6 +17763,8 @@ class basic_json
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@param[in] args arguments to forward to a constructor of @ref basic_json
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@tparam Args compatible types to create a @ref basic_json object
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@return reference to the inserted element
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@throw type_error.311 when called on a type other than JSON array or
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null; example: `"cannot use emplace_back() with number"`
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@ -17772,10 +17774,10 @@ class basic_json
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elements to a JSON array. Note how the `null` value was silently converted
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to a JSON array.,emplace_back}
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@since version 2.0.8
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@since version 2.0.8, returns reference since 3.7.0
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*/
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template<class... Args>
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void emplace_back(Args&& ... args)
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reference emplace_back(Args&& ... args)
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{
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// emplace_back only works for null objects or arrays
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if (JSON_UNLIKELY(not(is_null() or is_array())))
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@ -17792,7 +17794,12 @@ class basic_json
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}
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// add element to array (perfect forwarding)
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#ifdef JSON_HAS_CPP_17
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return m_value.array->emplace_back(std::forward<Args>(args)...);
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#else
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m_value.array->emplace_back(std::forward<Args>(args)...);
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return m_value.array->back();
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#endif
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}
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/*!
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@ -290,8 +290,10 @@ TEST_CASE("modifiers")
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SECTION("null")
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{
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json j;
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j.emplace_back(1);
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j.emplace_back(2);
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auto& x1 = j.emplace_back(1);
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CHECK(x1 == 1);
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auto& x2 = j.emplace_back(2);
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CHECK(x2 == 2);
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CHECK(j.type() == json::value_t::array);
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CHECK(j == json({1, 2}));
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}
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@ -299,7 +301,8 @@ TEST_CASE("modifiers")
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SECTION("array")
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{
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json j = {1, 2, 3};
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j.emplace_back("Hello");
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auto& x = j.emplace_back("Hello");
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CHECK(x == "Hello");
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CHECK(j.type() == json::value_t::array);
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CHECK(j == json({1, 2, 3, "Hello"}));
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}
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@ -307,7 +310,8 @@ TEST_CASE("modifiers")
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SECTION("multiple values")
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{
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json j;
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j.emplace_back(3, "foo");
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auto& x = j.emplace_back(3, "foo");
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CHECK(x == json({"foo", "foo", "foo"}));
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CHECK(j.type() == json::value_t::array);
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CHECK(j == json({{"foo", "foo", "foo"}}));
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}
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