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[C++] Generate default member initializers for >= C++11 (#5989)

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In >= C++11 mode, generate default member initializers instead of a
default constructor.

The new code is semantically equivalent, but will allow aggregate
initialization in C++20.

This is a different take on #5951.
This commit is contained in:
Jean-François Roy
2020-06-22 18:06:15 -07:00
committed by GitHub
parent 413bb9b553
commit e5a8f76a4b
2 changed files with 86 additions and 112 deletions
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27
src/idl_gen_cpp.cpp
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@@ -1652,15 +1652,38 @@ class CppGenerator : public BaseGenerator {
"> "
: GenTypeNativePtr(cpp_type->constant, &field, false))
: type + " ");
// Generate default member initializers for >= C++11.
std::string field_di = "";
if (opts_.g_cpp_std >= cpp::CPP_STD_11) {
field_di = "{}";
auto native_default = field.attributes.Lookup("native_default");
// Scalar types get parsed defaults, raw pointers get nullptrs.
if (IsScalar(field.value.type.base_type)) {
field_di =
" = " + (native_default ? std::string(native_default->constant)
: GetDefaultScalarValue(field, true));
} else if (field.value.type.base_type == BASE_TYPE_STRUCT) {
if (IsStruct(field.value.type) && native_default) {
field_di = " = " + native_default->constant;
}
}
}
code_.SetValue("FIELD_TYPE", full_type);
code_.SetValue("FIELD_NAME", Name(field));
code_ += " {{FIELD_TYPE}}{{FIELD_NAME}};";
code_.SetValue("FIELD_DI", field_di);
code_ += " {{FIELD_TYPE}}{{FIELD_NAME}}{{FIELD_DI}};";
}
}
// Generate the default constructor for this struct. Properly initialize all
// scalar members with default values.
void GenDefaultConstructor(const StructDef &struct_def) {
code_.SetValue("NATIVE_NAME",
NativeName(Name(struct_def), &struct_def, opts_));
// In >= C++11, default member initializers are generated.
if (opts_.g_cpp_std >= cpp::CPP_STD_11) {
return;
}
std::string initializer_list;
for (auto it = struct_def.fields.vec.begin();
it != struct_def.fields.vec.end(); ++it) {
@@ -1698,8 +1721,6 @@ class CppGenerator : public BaseGenerator {
initializer_list = "\n : " + initializer_list;
}
code_.SetValue("NATIVE_NAME",
NativeName(Name(struct_def), &struct_def, opts_));
code_.SetValue("INIT_LIST", initializer_list);
code_ += " {{NATIVE_NAME}}(){{INIT_LIST}} {";