feat: support std::string_view in Value API (#1584)

This adds direct support for `std::string_view` when available (C++17
and above). The current API can be used with `std::string_view` via the
low-level two-pointer methods, but is not ergonomic. E.g., compare:

```
Json::Value node;
std::string foo, bar, baz;
std::string_view foo_sv, bar_sv, baz_sv;

// Efficient & readable:
node[foo][bar][baz];
// Less efficient, less readable:
node[std::string(foo_sv)][std::string(bar_sv)][std::string(baz_sv)];
// Efficient, but a lot less readable:
*node.demand(foo_sv.data(), foo_sv.data() + foo_sv.size())
    ->demand(bar_sv.data(), bar_sv.data() + bar_sv.size())
    ->demand(baz_sv.data(), baz_sv.data() + baz_sv.size())
// After this change, efficient & readable:
node[foo_sv][bar_sv][baz_sv];
```

*   The constructor can take a `std::string_view` parameter. The existing
    overloads taking `const std::string&` and `const char*` are still necessary
    to support assignment from those types.
*   `operator[]`, `get()`, `isMember()` and `removeMember()` take a
    `std::string_view` parameter. This supersedes the overloads taking
    `const std::string&` and `const char*`. The overloads taking a pair of
    pointers (begin, end) are preserved for source compatibility.
*   `getString()` has an overload with a `std::string_view` output parameter.
    The one with a pair of pointers is preserved for source compatibility.

Signed-off-by: Lev Kandel <lmakhlis@google.com>
Co-authored-by: Jordan Bayles <bayles.jordan@gmail.com>
This commit is contained in:
evalon32 2025-01-10 18:25:25 -05:00 committed by GitHub
parent 07a8fe6a23
commit 60ccc1f5de
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GPG Key ID: B5690EEEBB952194
2 changed files with 125 additions and 7 deletions

View File

@ -39,6 +39,10 @@
#endif #endif
#endif #endif
#if __cplusplus >= 201703L
#define JSONCPP_HAS_STRING_VIEW 1
#endif
#include <array> #include <array>
#include <exception> #include <exception>
#include <map> #include <map>
@ -46,6 +50,10 @@
#include <string> #include <string>
#include <vector> #include <vector>
#ifdef JSONCPP_HAS_STRING_VIEW
#include <string_view>
#endif
// Disable warning C4251: <data member>: <type> needs to have dll-interface to // Disable warning C4251: <data member>: <type> needs to have dll-interface to
// be used by... // be used by...
#if defined(JSONCPP_DISABLE_DLL_INTERFACE_WARNING) #if defined(JSONCPP_DISABLE_DLL_INTERFACE_WARNING)
@ -342,6 +350,9 @@ public:
*/ */
Value(const StaticString& value); Value(const StaticString& value);
Value(const String& value); Value(const String& value);
#ifdef JSONCPP_HAS_STRING_VIEW
Value(std::string_view value);
#endif
Value(bool value); Value(bool value);
Value(std::nullptr_t ptr) = delete; Value(std::nullptr_t ptr) = delete;
Value(const Value& other); Value(const Value& other);
@ -384,6 +395,12 @@ public:
* \return false if !string. (Seg-fault if str or end are NULL.) * \return false if !string. (Seg-fault if str or end are NULL.)
*/ */
bool getString(char const** begin, char const** end) const; bool getString(char const** begin, char const** end) const;
#ifdef JSONCPP_HAS_STRING_VIEW
/** Get string_view of string-value.
* \return false if !string. (Seg-fault if str is NULL.)
*/
bool getString(std::string_view* str) const;
#endif
Int asInt() const; Int asInt() const;
UInt asUInt() const; UInt asUInt() const;
#if defined(JSON_HAS_INT64) #if defined(JSON_HAS_INT64)
@ -470,6 +487,15 @@ public:
bool insert(ArrayIndex index, const Value& newValue); bool insert(ArrayIndex index, const Value& newValue);
bool insert(ArrayIndex index, Value&& newValue); bool insert(ArrayIndex index, Value&& newValue);
#ifdef JSONCPP_HAS_STRING_VIEW
/// Access an object value by name, create a null member if it does not exist.
/// \param key may contain embedded nulls.
Value& operator[](std::string_view key);
/// Access an object value by name, returns null if there is no member with
/// that name.
/// \param key may contain embedded nulls.
const Value& operator[](std::string_view key) const;
#else
/// Access an object value by name, create a null member if it does not exist. /// Access an object value by name, create a null member if it does not exist.
/// \note Because of our implementation, keys are limited to 2^30 -1 chars. /// \note Because of our implementation, keys are limited to 2^30 -1 chars.
/// Exceeding that will cause an exception. /// Exceeding that will cause an exception.
@ -484,6 +510,7 @@ public:
/// that name. /// that name.
/// \param key may contain embedded nulls. /// \param key may contain embedded nulls.
const Value& operator[](const String& key) const; const Value& operator[](const String& key) const;
#endif
/** \brief Access an object value by name, create a null member if it does not /** \brief Access an object value by name, create a null member if it does not
* exist. * exist.
* *
@ -497,18 +524,24 @@ public:
* \endcode * \endcode
*/ */
Value& operator[](const StaticString& key); Value& operator[](const StaticString& key);
#ifdef JSONCPP_HAS_STRING_VIEW
/// Return the member named key if it exist, defaultValue otherwise.
/// \note deep copy
Value get(std::string_view key, const Value& defaultValue) const;
#else
/// Return the member named key if it exist, defaultValue otherwise. /// Return the member named key if it exist, defaultValue otherwise.
/// \note deep copy /// \note deep copy
Value get(const char* key, const Value& defaultValue) const; Value get(const char* key, const Value& defaultValue) const;
/// Return the member named key if it exist, defaultValue otherwise.
/// \note deep copy
/// \param key may contain embedded nulls.
Value get(const String& key, const Value& defaultValue) const;
#endif
/// Return the member named key if it exist, defaultValue otherwise. /// Return the member named key if it exist, defaultValue otherwise.
/// \note deep copy /// \note deep copy
/// \note key may contain embedded nulls. /// \note key may contain embedded nulls.
Value get(const char* begin, const char* end, Value get(const char* begin, const char* end,
const Value& defaultValue) const; const Value& defaultValue) const;
/// Return the member named key if it exist, defaultValue otherwise.
/// \note deep copy
/// \param key may contain embedded nulls.
Value get(const String& key, const Value& defaultValue) const;
/// Most general and efficient version of isMember()const, get()const, /// Most general and efficient version of isMember()const, get()const,
/// and operator[]const /// and operator[]const
/// \note As stated elsewhere, behavior is undefined if (end-begin) >= 2^30 /// \note As stated elsewhere, behavior is undefined if (end-begin) >= 2^30
@ -525,20 +558,28 @@ public:
/// Do nothing if it did not exist. /// Do nothing if it did not exist.
/// \pre type() is objectValue or nullValue /// \pre type() is objectValue or nullValue
/// \post type() is unchanged /// \post type() is unchanged
#if JSONCPP_HAS_STRING_VIEW
void removeMember(std::string_view key);
#else
void removeMember(const char* key); void removeMember(const char* key);
/// Same as removeMember(const char*) /// Same as removeMember(const char*)
/// \param key may contain embedded nulls. /// \param key may contain embedded nulls.
void removeMember(const String& key); void removeMember(const String& key);
/// Same as removeMember(const char* begin, const char* end, Value* removed), #endif
/// but 'key' is null-terminated.
bool removeMember(const char* key, Value* removed);
/** \brief Remove the named map member. /** \brief Remove the named map member.
* *
* Update 'removed' iff removed. * Update 'removed' iff removed.
* \param key may contain embedded nulls. * \param key may contain embedded nulls.
* \return true iff removed (no exceptions) * \return true iff removed (no exceptions)
*/ */
#if JSONCPP_HAS_STRING_VIEW
bool removeMember(std::string_view key, Value* removed);
#else
bool removeMember(String const& key, Value* removed); bool removeMember(String const& key, Value* removed);
/// Same as removeMember(const char* begin, const char* end, Value* removed),
/// but 'key' is null-terminated.
bool removeMember(const char* key, Value* removed);
#endif
/// Same as removeMember(String const& key, Value* removed) /// Same as removeMember(String const& key, Value* removed)
bool removeMember(const char* begin, const char* end, Value* removed); bool removeMember(const char* begin, const char* end, Value* removed);
/** \brief Remove the indexed array element. /** \brief Remove the indexed array element.
@ -549,12 +590,18 @@ public:
*/ */
bool removeIndex(ArrayIndex index, Value* removed); bool removeIndex(ArrayIndex index, Value* removed);
#ifdef JSONCPP_HAS_STRING_VIEW
/// Return true if the object has a member named key.
/// \param key may contain embedded nulls.
bool isMember(std::string_view key) const;
#else
/// Return true if the object has a member named key. /// Return true if the object has a member named key.
/// \note 'key' must be null-terminated. /// \note 'key' must be null-terminated.
bool isMember(const char* key) const; bool isMember(const char* key) const;
/// Return true if the object has a member named key. /// Return true if the object has a member named key.
/// \param key may contain embedded nulls. /// \param key may contain embedded nulls.
bool isMember(const String& key) const; bool isMember(const String& key) const;
#endif
/// Same as isMember(String const& key)const /// Same as isMember(String const& key)const
bool isMember(const char* begin, const char* end) const; bool isMember(const char* begin, const char* end) const;

View File

@ -17,6 +17,10 @@
#include <sstream> #include <sstream>
#include <utility> #include <utility>
#ifdef JSONCPP_HAS_STRING_VIEW
#include <string_view>
#endif
// Provide implementation equivalent of std::snprintf for older _MSC compilers // Provide implementation equivalent of std::snprintf for older _MSC compilers
#if defined(_MSC_VER) && _MSC_VER < 1900 #if defined(_MSC_VER) && _MSC_VER < 1900
#include <stdarg.h> #include <stdarg.h>
@ -420,6 +424,14 @@ Value::Value(const String& value) {
value.data(), static_cast<unsigned>(value.length())); value.data(), static_cast<unsigned>(value.length()));
} }
#ifdef JSONCPP_HAS_STRING_VIEW
Value::Value(std::string_view value) {
initBasic(stringValue, true);
value_.string_ = duplicateAndPrefixStringValue(
value.data(), static_cast<unsigned>(value.length()));
}
#endif
Value::Value(const StaticString& value) { Value::Value(const StaticString& value) {
initBasic(stringValue); initBasic(stringValue);
value_.string_ = const_cast<char*>(value.c_str()); value_.string_ = const_cast<char*>(value.c_str());
@ -627,6 +639,21 @@ bool Value::getString(char const** begin, char const** end) const {
return true; return true;
} }
#ifdef JSONCPP_HAS_STRING_VIEW
bool Value::getString(std::string_view* str) const {
if (type() != stringValue)
return false;
if (value_.string_ == nullptr)
return false;
const char* begin;
unsigned length;
decodePrefixedString(this->isAllocated(), this->value_.string_, &length,
&begin);
*str = std::string_view(begin, length);
return true;
}
#endif
String Value::asString() const { String Value::asString() const {
switch (type()) { switch (type()) {
case nullValue: case nullValue:
@ -1108,6 +1135,17 @@ Value* Value::demand(char const* begin, char const* end) {
"objectValue or nullValue"); "objectValue or nullValue");
return &resolveReference(begin, end); return &resolveReference(begin, end);
} }
#ifdef JSONCPP_HAS_STRING_VIEW
const Value& Value::operator[](std::string_view key) const {
Value const* found = find(key.data(), key.data() + key.length());
if (!found)
return nullSingleton();
return *found;
}
Value& Value::operator[](std::string_view key) {
return resolveReference(key.data(), key.data() + key.length());
}
#else
const Value& Value::operator[](const char* key) const { const Value& Value::operator[](const char* key) const {
Value const* found = find(key, key + strlen(key)); Value const* found = find(key, key + strlen(key));
if (!found) if (!found)
@ -1128,6 +1166,7 @@ Value& Value::operator[](const char* key) {
Value& Value::operator[](const String& key) { Value& Value::operator[](const String& key) {
return resolveReference(key.data(), key.data() + key.length()); return resolveReference(key.data(), key.data() + key.length());
} }
#endif
Value& Value::operator[](const StaticString& key) { Value& Value::operator[](const StaticString& key) {
return resolveReference(key.c_str()); return resolveReference(key.c_str());
@ -1167,12 +1206,18 @@ Value Value::get(char const* begin, char const* end,
Value const* found = find(begin, end); Value const* found = find(begin, end);
return !found ? defaultValue : *found; return !found ? defaultValue : *found;
} }
#ifdef JSONCPP_HAS_STRING_VIEW
Value Value::get(std::string_view key, const Value& defaultValue) const {
return get(key.data(), key.data() + key.length(), defaultValue);
}
#else
Value Value::get(char const* key, Value const& defaultValue) const { Value Value::get(char const* key, Value const& defaultValue) const {
return get(key, key + strlen(key), defaultValue); return get(key, key + strlen(key), defaultValue);
} }
Value Value::get(String const& key, Value const& defaultValue) const { Value Value::get(String const& key, Value const& defaultValue) const {
return get(key.data(), key.data() + key.length(), defaultValue); return get(key.data(), key.data() + key.length(), defaultValue);
} }
#endif
bool Value::removeMember(const char* begin, const char* end, Value* removed) { bool Value::removeMember(const char* begin, const char* end, Value* removed) {
if (type() != objectValue) { if (type() != objectValue) {
@ -1188,12 +1233,31 @@ bool Value::removeMember(const char* begin, const char* end, Value* removed) {
value_.map_->erase(it); value_.map_->erase(it);
return true; return true;
} }
#ifdef JSONCPP_HAS_STRING_VIEW
bool Value::removeMember(std::string_view key, Value* removed) {
return removeMember(key.data(), key.data() + key.length(), removed);
}
#else
bool Value::removeMember(const char* key, Value* removed) { bool Value::removeMember(const char* key, Value* removed) {
return removeMember(key, key + strlen(key), removed); return removeMember(key, key + strlen(key), removed);
} }
bool Value::removeMember(String const& key, Value* removed) { bool Value::removeMember(String const& key, Value* removed) {
return removeMember(key.data(), key.data() + key.length(), removed); return removeMember(key.data(), key.data() + key.length(), removed);
} }
#endif
#ifdef JSONCPP_HAS_STRING_VIEW
void Value::removeMember(std::string_view key) {
JSON_ASSERT_MESSAGE(type() == nullValue || type() == objectValue,
"in Json::Value::removeMember(): requires objectValue");
if (type() == nullValue)
return;
CZString actualKey(key.data(), unsigned(key.length()),
CZString::noDuplication);
value_.map_->erase(actualKey);
}
#else
void Value::removeMember(const char* key) { void Value::removeMember(const char* key) {
JSON_ASSERT_MESSAGE(type() == nullValue || type() == objectValue, JSON_ASSERT_MESSAGE(type() == nullValue || type() == objectValue,
"in Json::Value::removeMember(): requires objectValue"); "in Json::Value::removeMember(): requires objectValue");
@ -1204,6 +1268,7 @@ void Value::removeMember(const char* key) {
value_.map_->erase(actualKey); value_.map_->erase(actualKey);
} }
void Value::removeMember(const String& key) { removeMember(key.c_str()); } void Value::removeMember(const String& key) { removeMember(key.c_str()); }
#endif
bool Value::removeIndex(ArrayIndex index, Value* removed) { bool Value::removeIndex(ArrayIndex index, Value* removed) {
if (type() != arrayValue) { if (type() != arrayValue) {
@ -1233,12 +1298,18 @@ bool Value::isMember(char const* begin, char const* end) const {
Value const* value = find(begin, end); Value const* value = find(begin, end);
return nullptr != value; return nullptr != value;
} }
#ifdef JSONCPP_HAS_STRING_VIEW
bool Value::isMember(std::string_view key) const {
return isMember(key.data(), key.data() + key.length());
}
#else
bool Value::isMember(char const* key) const { bool Value::isMember(char const* key) const {
return isMember(key, key + strlen(key)); return isMember(key, key + strlen(key));
} }
bool Value::isMember(String const& key) const { bool Value::isMember(String const& key) const {
return isMember(key.data(), key.data() + key.length()); return isMember(key.data(), key.data() + key.length());
} }
#endif
Value::Members Value::getMemberNames() const { Value::Members Value::getMemberNames() const {
JSON_ASSERT_MESSAGE( JSON_ASSERT_MESSAGE(