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Add ::Set function to Unions to make memory ownership clear.

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Unions own the NativeTable* value member because they need to destroy them
when the Union goes out of scope.  Currently, the data is destroyed by calling
delete, which means that the member needs to be allocated with new.  However,
making the allocation the responsibility of the client and the destruction
the responsibility of the Union can lead to potential errors.  Adding a
Set function will ensure that the memory is allocated correctly so that it
can be deleted later.

From cl/142161569.

Change-Id: I4605f26d2749164819bfae0140e5fae08442b50a
This commit is contained in:
Wouter van Oortmerssen
2016-12-19 15:21:08 -08:00
parent d1e8899310
commit c66683f27f
3 changed files with 112 additions and 69 deletions
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85
src/idl_gen_cpp.cpp
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@@ -472,36 +472,6 @@ class CppGenerator : public BaseGenerator {
GenTypeBasic(enum_def.underlying_type, false) + ")\n";
code += "\n";
if (parser_.opts.generate_object_based_api && enum_def.is_union) {
// Generate a union type
code += "struct " + enum_def.name + "Union {\n";
code += " " + enum_def.name + " type;\n\n";
code += " flatbuffers::NativeTable *table;\n";
code += " " + enum_def.name + "Union() : type(";
code += GetEnumValUse(enum_def, *enum_def.vals.Lookup("NONE"), parser_.opts);
code += "), table(nullptr) {}\n";
code += " " + enum_def.name + "Union(const ";
code += enum_def.name + "Union &);\n";
code += " " + enum_def.name + "Union &operator=(const ";
code += enum_def.name + "Union &);\n";
code += " ~" + enum_def.name + "Union();\n\n";
code += " " + UnionUnPackSignature(enum_def, true) + ";\n";
code += " " + UnionPackSignature(enum_def, true) + ";\n\n";
for (auto it = enum_def.vals.vec.begin(); it != enum_def.vals.vec.end();
++it) {
auto &ev = **it;
if (ev.value) {
auto native_name = NativeName(WrapInNameSpace(*ev.struct_def));
code += " " + native_name + " *As";
code += ev.name + "() { return type == ";
code += GetEnumValUse(enum_def, ev, parser_.opts);
code += " ? reinterpret_cast<" + native_name;
code += " *>(table) : nullptr; }\n";
}
}
code += "};\n\n";
}
// Generate a generate string table for enum values.
// Problem is, if values are very sparse that could generate really big
// tables. Ideally in that case we generate a map lookup instead, but for
@@ -552,6 +522,50 @@ class CppGenerator : public BaseGenerator {
}
}
if (parser_.opts.generate_object_based_api && enum_def.is_union) {
// Generate a union type
code += "struct " + enum_def.name + "Union {\n";
code += " " + enum_def.name + " type = ";
code += GetEnumValUse(enum_def, *enum_def.vals.Lookup("NONE"), parser_.opts);
code += ";\n\n";
code += " flatbuffers::NativeTable *table = nullptr;\n";
code += " " + enum_def.name + "Union() : type(";
code += GetEnumValUse(enum_def, *enum_def.vals.Lookup("NONE"), parser_.opts);
code += "), table(nullptr) {}\n";
code += " " + enum_def.name + "Union(const ";
code += enum_def.name + "Union &);\n";
code += " " + enum_def.name + "Union &operator=(const ";
code += enum_def.name + "Union &);\n";
code += " ~" + enum_def.name + "Union() { Reset(); }\n";
code += " void Reset();\n\n";
code += " template <typename T>\n";
code += " void Set(T&& value) {\n";
code += " Reset();\n";
code += " type = " + enum_def.name;
code += "Traits<typename T::TableType>::enum_value;\n";
code += " if (type != ";
code += GetEnumValUse(enum_def, *enum_def.vals.Lookup("NONE"), parser_.opts);
code += ") {\n";
code += " table = new T(std::forward<T>(value));\n";
code += " }\n";
code += " }\n\n";
code += " " + UnionUnPackSignature(enum_def, true) + ";\n";
code += " " + UnionPackSignature(enum_def, true) + ";\n\n";
for (auto it = enum_def.vals.vec.begin(); it != enum_def.vals.vec.end();
++it) {
auto &ev = **it;
if (ev.value) {
auto native_name = NativeName(WrapInNameSpace(*ev.struct_def));
code += " " + native_name + " *As";
code += ev.name + "() { return type == ";
code += GetEnumValUse(enum_def, ev, parser_.opts);
code += " ? reinterpret_cast<" + native_name;
code += " *>(table) : nullptr; }\n";
}
}
code += "};\n\n";
}
if (enum_def.is_union) {
code += UnionVerifySignature(enum_def) + ";\n\n";
}
@@ -614,8 +628,7 @@ class CppGenerator : public BaseGenerator {
code += " default: return 0;\n }\n}\n\n";
// Generate a union destructor.
code += "inline " + enum_def.name + "Union::~";
code += enum_def.name + "Union() {\n";
code += "inline void " + enum_def.name + "Union::Reset() {\n";
code += " switch (type) {\n";
for (auto it = enum_def.vals.vec.begin(); it != enum_def.vals.vec.end();
++it) {
@@ -627,7 +640,13 @@ class CppGenerator : public BaseGenerator {
code += " *>(table); break;\n";
}
}
code += " default:;\n }\n}\n\n";
code += " default: break;\n";
code += " }\n";
code += " table = nullptr;\n";
code += " type = ";
code += GetEnumValUse(enum_def, *enum_def.vals.Lookup("NONE"), parser_.opts);
code += ";\n";
code += "}\n\n";
}
}