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feat: support std::string_view in Value API

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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>
This commit is contained in:
Lev Kandel 2024-12-08 18:14:56 +00:00
parent dca8a24cf8
commit dbff9dba38
2 changed files with 125 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

61
include/json/value.h
View File

@ -39,6 +39,10 @@
#endif
#endif
#if __cplusplus >= 201703L
#define JSONCPP_HAS_STRING_VIEW 1
#endif
#include <array>
#include <exception>
#include <map>
@ -46,6 +50,10 @@
#include <string>
#include <vector>
#ifdef JSONCPP_HAS_STRING_VIEW
#include <string_view>
#endif
// Disable warning C4251: <data member>: <type> needs to have dll-interface to
// be used by...
#if defined(JSONCPP_DISABLE_DLL_INTERFACE_WARNING)
@ -342,6 +350,9 @@ public:
*/
Value(const StaticString& value);
Value(const String& value);
#ifdef JSONCPP_HAS_STRING_VIEW
Value(std::string_view value);
#endif
Value(bool value);
Value(std::nullptr_t ptr) = delete;
Value(const Value& other);
@ -384,6 +395,12 @@ public:
* \return false if !string. (Seg-fault if str or end are NULL.)
*/
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;
UInt asUInt() const;
#if defined(JSON_HAS_INT64)
@ -470,6 +487,15 @@ public:
bool insert(ArrayIndex index, const 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.
/// \note Because of our implementation, keys are limited to 2^30 -1 chars.
/// Exceeding that will cause an exception.
@ -484,6 +510,7 @@ public:
/// that name.
/// \param key may contain embedded nulls.
const Value& operator[](const String& key) const;
#endif
/** \brief Access an object value by name, create a null member if it does not
* exist.
*
@ -497,18 +524,24 @@ public:
* \endcode
*/
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.
/// \note deep copy
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.
/// \note deep copy
/// \note key may contain embedded nulls.
Value get(const char* begin, const char* end,
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,
/// and operator[]const
/// \note As stated elsewhere, behavior is undefined if (end-begin) >= 2^30
@ -525,20 +558,28 @@ public:
/// Do nothing if it did not exist.
/// \pre type() is objectValue or nullValue
/// \post type() is unchanged
#if JSONCPP_HAS_STRING_VIEW
void removeMember(std::string_view key);
#else
void removeMember(const char* key);
/// Same as removeMember(const char*)
/// \param key may contain embedded nulls.
void removeMember(const String& key);
/// Same as removeMember(const char* begin, const char* end, Value* removed),
/// but 'key' is null-terminated.
bool removeMember(const char* key, Value* removed);
#endif
/** \brief Remove the named map member.
*
* Update 'removed' iff removed.
* \param key may contain embedded nulls.
* \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);
/// 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)
bool removeMember(const char* begin, const char* end, Value* removed);
/** \brief Remove the indexed array element.
@ -549,12 +590,18 @@ public:
*/
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.
/// \note 'key' must be null-terminated.
bool isMember(const char* key) const;
/// Return true if the object has a member named key.
/// \param key may contain embedded nulls.
bool isMember(const String& key) const;
#endif
/// Same as isMember(String const& key)const
bool isMember(const char* begin, const char* end) const;

71
src/lib_json/json_value.cpp
View File

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