repeated_ptr_field.h -- document lifetime of pointers and references
@jguamie ya está trabajando en esto.
Desde el 17/10/2025.
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Descripción
In STL containers that store value elements (e.g. vector<Bar> as opposed to vector<Bar*>), element pointers are invalidated by operations such as adding or removing elements from the container.
The generated C++ code for repeated message fields returns a container of value elements:
https://protobuf.dev/reference/cpp/cpp-generated/#repeatedmessage
const RepeatedPtrField<Bar>& bar()
RepeatedPtrField<Bar>* mutable_bar()
However, based on the "Ptr" in the name, and looking at the current implementation, it seems that the intention is for RepeatedPtrField to behave more like vector<Foo*>, where it is safe to hold on to pointers to the underlying messages.
For example, is this safe?:
message Bar {
string baz = 1;
}
message Foo {
repeated Bar bar = 1;
}
...
std::string do_something(Foo *foo) {
// Get a reference to first element of bar
const Bar& bar = *foo->bar()->begin();
// Add a bar to foo
foo->add_bar();
// Do something with the first bar reference
return bar.baz();
}
I'm not finding clear documentation on this behavior though. Assuming it is meant to be safe to hold on to these references/pointers, could this please be documented?
Related stack overflow making the same assumption:
https://stackoverflow.com/questions/33219022/do-pointers-to-items-of-a-repeated-gpb-field-stay-valid-if-the-field-is-modified
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