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✨ make emplace_back return a reference #1609

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Niels Lohmann 2019-06-30 12:19:41 +02:00
parent 9a775bcb14
commit 1be63431f3
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GPG key ID: 7F3CEA63AE251B69
3 changed files with 26 additions and 8 deletions
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11
include/nlohmann/json.hpp
View file

@ -4952,6 +4952,8 @@ class basic_json
@param[in] args arguments to forward to a constructor of @ref basic_json
@tparam Args compatible types to create a @ref basic_json object
@return reference to the inserted element
@throw type_error.311 when called on a type other than JSON array or
null; example: `"cannot use emplace_back() with number"`
@ -4961,10 +4963,10 @@ class basic_json
elements to a JSON array. Note how the `null` value was silently converted
to a JSON array.,emplace_back}
@since version 2.0.8
@since version 2.0.8, returns reference since 3.7.0
*/
template<class... Args>
void emplace_back(Args&& ... args)
reference emplace_back(Args&& ... args)
{
// emplace_back only works for null objects or arrays
if (JSON_UNLIKELY(not(is_null() or is_array())))
@ -4981,7 +4983,12 @@ class basic_json
}
// add element to array (perfect forwarding)
#ifdef JSON_HAS_CPP_17
return m_value.array->emplace_back(std::forward<Args>(args)...);
#else
m_value.array->emplace_back(std::forward<Args>(args)...);
return m_value.array->back();
#endif
}
/*!

11
single_include/nlohmann/json.hpp
View file

@ -17763,6 +17763,8 @@ class basic_json
@param[in] args arguments to forward to a constructor of @ref basic_json
@tparam Args compatible types to create a @ref basic_json object
@return reference to the inserted element
@throw type_error.311 when called on a type other than JSON array or
null; example: `"cannot use emplace_back() with number"`
@ -17772,10 +17774,10 @@ class basic_json
elements to a JSON array. Note how the `null` value was silently converted
to a JSON array.,emplace_back}
@since version 2.0.8
@since version 2.0.8, returns reference since 3.7.0
*/
template<class... Args>
void emplace_back(Args&& ... args)
reference emplace_back(Args&& ... args)
{
// emplace_back only works for null objects or arrays
if (JSON_UNLIKELY(not(is_null() or is_array())))
@ -17792,7 +17794,12 @@ class basic_json
}
// add element to array (perfect forwarding)
#ifdef JSON_HAS_CPP_17
return m_value.array->emplace_back(std::forward<Args>(args)...);
#else
m_value.array->emplace_back(std::forward<Args>(args)...);
return m_value.array->back();
#endif
}
/*!

12
test/src/unit-modifiers.cpp
View file

@ -290,8 +290,10 @@ TEST_CASE("modifiers")
SECTION("null")
{
json j;
j.emplace_back(1);
j.emplace_back(2);
auto& x1 = j.emplace_back(1);
CHECK(x1 == 1);
auto& x2 = j.emplace_back(2);
CHECK(x2 == 2);
CHECK(j.type() == json::value_t::array);
CHECK(j == json({1, 2}));
}
@ -299,7 +301,8 @@ TEST_CASE("modifiers")
SECTION("array")
{
json j = {1, 2, 3};
j.emplace_back("Hello");
auto& x = j.emplace_back("Hello");
CHECK(x == "Hello");
CHECK(j.type() == json::value_t::array);
CHECK(j == json({1, 2, 3, "Hello"}));
}
@ -307,7 +310,8 @@ TEST_CASE("modifiers")
SECTION("multiple values")
{
json j;
j.emplace_back(3, "foo");
auto& x = j.emplace_back(3, "foo");
CHECK(x == json({"foo", "foo", "foo"}));
CHECK(j.type() == json::value_t::array);
CHECK(j == json({{"foo", "foo", "foo"}}));
}