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emaxerrnoaardappel
emaxerrno
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aardappel
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Add arbitrary string type to the native object API (google#4218)
* Custom strings are very common for optimizations around small objects or growth style optimizations, i.e.: grow at 1.57 times vs doubling vs.. A second common strategy is to cooperate w/ the memory allocator see FBString[1] and seastar[2] string for examples. [1] fbstring: https://github.com/facebook/folly/blob/master/folly/docs/FBString.md [2] sstring: https://github.com/scylladb/seastar/blob/master/core/sstring.hh
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‎docs/source/CppUsage.md‎

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@@ -200,6 +200,15 @@ pointer type (`my_ptr<T>`), or by specifying `naked` as the type to get `T *`
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pointers. Unlike the smart pointers, naked pointers do not manage memory for
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you, so you'll have to manage their lifecycles manually.
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# Using different string type.
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By default the object tree is built out of `std::string`, but you can
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influence this either globally (using the `--cpp-str-type` argument to
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`flatc`) or per field using the `cpp_str_type` attribute.
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The type must support T::c_str() and T::length() as member functions.
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## Reflection (& Resizing)
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There is experimental support for reflection in FlatBuffers, allowing you to

‎include/flatbuffers/flatbuffers.h‎

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@@ -980,6 +980,15 @@ FLATBUFFERS_FINAL_CLASS
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return str ? CreateString(str->c_str(), str->Length()) : 0;
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}
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/// @brief Store a string in the buffer, which can contain any binary data.
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/// @param[in] str A const reference to a std::string like type with support
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/// of T::c_str() and T::length() to store in the buffer.
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/// @return Returns the offset in the buffer where the string starts.
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template<typename T>
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Offset<String> CreateString(const T &str) {
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return CreateString(str.c_str(), str.length());
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}
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/// @brief Store a string in the buffer, which can contain any binary data.
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/// If a string with this exact contents has already been serialized before,
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/// instead simply returns the offset of the existing string.

‎include/flatbuffers/idl.h‎

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@@ -353,6 +353,7 @@ struct IDLOptions {
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bool escape_proto_identifiers;
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bool generate_object_based_api;
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std::string cpp_object_api_pointer_type;
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std::string cpp_object_api_string_type;
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bool union_value_namespacing;
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bool allow_non_utf8;
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std::string include_prefix;
@@ -479,6 +480,7 @@ class Parser : public ParserState {
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known_attributes_["idempotent"] = true;
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known_attributes_["cpp_type"] = true;
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known_attributes_["cpp_ptr_type"] = true;
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known_attributes_["cpp_str_type"] = true;
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known_attributes_["native_inline"] = true;
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known_attributes_["native_type"] = true;
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known_attributes_["native_default"] = true;
@@ -743,4 +745,3 @@ bool GenerateGoGRPC(const Parser &parser,
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} // namespace flatbuffers
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#endif // FLATBUFFERS_IDL_H_
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‎src/flatc.cpp‎

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@@ -86,6 +86,8 @@ std::string FlatCompiler::GetUsageString(const char* program_name) const {
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" --escape-proto-ids Disable appending '_' in namespaces names.\n"
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" --gen-object-api Generate an additional object-based API.\n"
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" --cpp-ptr-type T Set object API pointer type (default std::unique_ptr)\n"
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" --cpp-str-type T Set object API string type (default std::string)\n"
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" T::c_str() and T::length() must be supported\n"
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" --no-js-exports Removes Node.js style export lines in JS.\n"
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" --goog-js-export Uses goog.exports* for closure compiler exporting in JS.\n"
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" --raw-binary Allow binaries without file_indentifier to be read.\n"
@@ -178,6 +180,9 @@ int FlatCompiler::Compile(int argc, const char** argv) {
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} else if (arg == "--cpp-ptr-type") {
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if (++argi >= argc) Error("missing type following" + arg, true);
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opts.cpp_object_api_pointer_type = argv[argi];
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} else if (arg == "--cpp-str-type") {
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if (++argi >= argc) Error("missing type following" + arg, true);
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opts.cpp_object_api_string_type = argv[argi];
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} else if(arg == "--gen-all") {
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opts.generate_all = true;
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opts.include_dependence_headers = false;

‎src/idl_gen_cpp.cpp‎

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@@ -362,6 +362,15 @@ class CppGenerator : public BaseGenerator {
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return attr ? attr->constant : parser_.opts.cpp_object_api_pointer_type;
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}
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const std::string NativeString(const FieldDef *field) {
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auto attr = field ? field->attributes.Lookup("cpp_str_type") : nullptr;
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auto &ret = attr ? attr->constant : parser_.opts.cpp_object_api_string_type;
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if (ret.empty()) {
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return "std::string";
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}
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return ret;
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}
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std::string GenTypeNativePtr(const std::string &type, const FieldDef *field,
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bool is_constructor) {
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auto &ptr_type = PtrType(field);
@@ -383,7 +392,7 @@ class CppGenerator : public BaseGenerator {
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const FieldDef &field) {
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switch (type.base_type) {
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case BASE_TYPE_STRING: {
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return "std::string";
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return NativeString(&field);
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}
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case BASE_TYPE_VECTOR: {
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const auto type_name = GenTypeNative(type.VectorType(), true, field);

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