[capnproto] Can't move unique pointer to MallocMessageBuilder

[k***@gmail.com]

I'm trying to figure out how to move a MallocMessageBuilder. I thought that
if I created a std::unique_ptr to it, then I could move that pointer, but
it is failing at runtime because the rvalue constructor is deleted.

Am I doing something wrong with my move?

Pseudo-code:
void my_func(std::unique_ptr<::capnp::MallocMessageBuilder> builder) {
my_class.builder = std::move(builder);
}
auto builder = std::unique_ptr<::capnp::MallocMessageBuilder>();
// ... initialize the builder ...
my_func(std::move(builder));

Is there a way to move a MallocMessageBuilder without just using a raw
pointer? It fails at runtime in the std::move call in my function.

Thanks!

['Kenton Varda' via Cap'n Proto]

Hi Kevin,

Moving a unique_ptr doesn't touch the pointed-to type at all, so the
problem here couldn't possibly have anything to do with
MallocMessageBuilder. I don't see anything obviously wrong with the code
you provided, so the bug must be elsewhere in your code. It is possible
that my_class is an invalid reference? What do you mean when you say that
std::move() "fails"? I honestly can't think of any way that std::move()
could fail at runtime, since it only casts one reference type to another.

-Kenton

Post by k***@gmail.com
I'm trying to figure out how to move a MallocMessageBuilder. I thought
that if I created a std::unique_ptr to it, then I could move that pointer,
but it is failing at runtime because the rvalue constructor is deleted.
Am I doing something wrong with my move?
void my_func(std::unique_ptr<::capnp::MallocMessageBuilder> builder) {
my_class.builder = std::move(builder);
}
auto builder = std::unique_ptr<::capnp::MallocMessageBuilder>();
// ... initialize the builder ...
my_func(std::move(builder));
Is there a way to move a MallocMessageBuilder without just using a raw
pointer? It fails at runtime in the std::move call in my function.
Thanks!
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[Kevin Greene]

You’re right, that doesn’t make any sense.

Turned out to be related to the fact that it was being called in a
constructor, and some unrelated things weren’t initialized yet. I had just
gotten confused by the backtrace output.

Sorry for the noise.

Post by 'Kenton Varda' via Cap'n Proto
Hi Kevin,
Moving a unique_ptr doesn't touch the pointed-to type at all, so the
problem here couldn't possibly have anything to do with
MallocMessageBuilder. I don't see anything obviously wrong with the code
you provided, so the bug must be elsewhere in your code. It is possible
that my_class is an invalid reference? What do you mean when you say that
std::move() "fails"? I honestly can't think of any way that std::move()
could fail at runtime, since it only casts one reference type to another.
-Kenton

Post by k***@gmail.com
I'm trying to figure out how to move a MallocMessageBuilder. I thought
that if I created a std::unique_ptr to it, then I could move that pointer,
but it is failing at runtime because the rvalue constructor is deleted.
Am I doing something wrong with my move?
void my_func(std::unique_ptr<::capnp::MallocMessageBuilder> builder) {
my_class.builder = std::move(builder);
}
auto builder = std::unique_ptr<::capnp::MallocMessageBuilder>();
// ... initialize the builder ...
my_func(std::move(builder));
Is there a way to move a MallocMessageBuilder without just using a raw
pointer? It fails at runtime in the std::move call in my function.
Thanks!

--

Post by k***@gmail.com
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