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Use a Myers Singleton for null

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Avoid some static initialization problems.

From @marklakata
See #488
This commit is contained in:
Christopher Dunn 2016-06-26 18:47:43 -05:00
parent e0f9aab0bf
commit 0f288aecdd
2 changed files with 30 additions and 16 deletions
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2
include/json/value.h
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@ -190,6 +190,8 @@ public:
static const Value& null; ///< We regret this reference to a global instance; prefer the simpler Value().
static const Value& nullRef; ///< just a kludge for binary-compatibility; same as null
static Value const& nullSingleton(); ///< Prefer this to null or nullRef.
/// Minimum signed integer value that can be stored in a Json::Value.
static const LargestInt minLargestInt;
/// Maximum signed integer value that can be stored in a Json::Value.

44
src/lib_json/json_value.cpp
View File

@ -31,10 +31,22 @@ namespace Json {
#else
#define ALIGNAS(byte_alignment)
#endif
static const unsigned char ALIGNAS(8) kNull[sizeof(Value)] = { 0 };
const unsigned char& kNullRef = kNull[0];
const Value& Value::null = reinterpret_cast<const Value&>(kNullRef);
const Value& Value::nullRef = null;
//static const unsigned char ALIGNAS(8) kNull[sizeof(Value)] = { 0 };
//const unsigned char& kNullRef = kNull[0];
//const Value& Value::null = reinterpret_cast<const Value&>(kNullRef);
//const Value& Value::nullRef = null;
// static
Value const& Value::nullSingleton()
{
static Value const* nullStatic = new Value;
return *nullStatic;
}
// for backwards compatibility, we'll leave these global references around, but DO NOT
// use them in JSONCPP library code any more!
Value const& Value::null = Value::nullSingleton();
Value const& Value::nullRef = Value::nullSingleton();
const Int Value::minInt = Int(~(UInt(-1) / 2));
const Int Value::maxInt = Int(UInt(-1) / 2);
@ -972,7 +984,7 @@ Value& Value::operator[](ArrayIndex index) {
if (it != value_.map_->end() && (*it).first == key)
return (*it).second;
ObjectValues::value_type defaultValue(key, nullRef);
ObjectValues::value_type defaultValue(key, nullSingleton());
it = value_.map_->insert(it, defaultValue);
return (*it).second;
}
@ -989,11 +1001,11 @@ const Value& Value::operator[](ArrayIndex index) const {
type_ == nullValue || type_ == arrayValue,
"in Json::Value::operator[](ArrayIndex)const: requires arrayValue");
if (type_ == nullValue)
return nullRef;
return nullSingleton();
CZString key(index);
ObjectValues::const_iterator it = value_.map_->find(key);
if (it == value_.map_->end())
return nullRef;
return nullSingleton();
return (*it).second;
}
@ -1027,7 +1039,7 @@ Value& Value::resolveReference(const char* key) {
if (it != value_.map_->end() && (*it).first == actualKey)
return (*it).second;
ObjectValues::value_type defaultValue(actualKey, nullRef);
ObjectValues::value_type defaultValue(actualKey, nullSingleton());
it = value_.map_->insert(it, defaultValue);
Value& value = (*it).second;
return value;
@ -1047,7 +1059,7 @@ Value& Value::resolveReference(char const* key, char const* cend)
if (it != value_.map_->end() && (*it).first == actualKey)
return (*it).second;
ObjectValues::value_type defaultValue(actualKey, nullRef);
ObjectValues::value_type defaultValue(actualKey, nullSingleton());
it = value_.map_->insert(it, defaultValue);
Value& value = (*it).second;
return value;
@ -1055,7 +1067,7 @@ Value& Value::resolveReference(char const* key, char const* cend)
Value Value::get(ArrayIndex index, const Value& defaultValue) const {
const Value* value = &((*this)[index]);
return value == &nullRef ? defaultValue : *value;
return value == &nullSingleton() ? defaultValue : *value;
}
bool Value::isValidIndex(ArrayIndex index) const { return index < size(); }
@ -1074,13 +1086,13 @@ Value const* Value::find(char const* key, char const* cend) const
const Value& Value::operator[](const char* key) const
{
Value const* found = find(key, key + strlen(key));
if (!found) return nullRef;
if (!found) return nullSingleton();
return *found;
}
Value const& Value::operator[](JSONCPP_STRING const& key) const
{
Value const* found = find(key.data(), key.data() + key.length());
if (!found) return nullRef;
if (!found) return nullSingleton();
return *found;
}
@ -1103,7 +1115,7 @@ Value& Value::operator[](const CppTL::ConstString& key) {
Value const& Value::operator[](CppTL::ConstString const& key) const
{
Value const* found = find(key.c_str(), key.end_c_str());
if (!found) return nullRef;
if (!found) return nullSingleton();
return *found;
}
#endif
@ -1151,7 +1163,7 @@ Value Value::removeMember(const char* key)
JSON_ASSERT_MESSAGE(type_ == nullValue || type_ == objectValue,
"in Json::Value::removeMember(): requires objectValue");
if (type_ == nullValue)
return nullRef;
return nullSingleton();
Value removed; // null
removeMember(key, key + strlen(key), &removed);
@ -1538,7 +1550,7 @@ const Value& Path::resolve(const Value& root) const {
// Error: unable to resolve path (object value expected at position...)
}
node = &((*node)[arg.key_]);
if (node == &Value::nullRef) {
if (node == &Value::nullSingleton()) {
// Error: unable to resolve path (object has no member named '' at
// position...)
}
@ -1559,7 +1571,7 @@ Value Path::resolve(const Value& root, const Value& defaultValue) const {
if (!node->isObject())
return defaultValue;
node = &((*node)[arg.key_]);
if (node == &Value::nullRef)
if (node == &Value::nullSingleton())
return defaultValue;
}
}