Libtorch IValue from std::vector<IValue>

1

What is the expected way to create an IValue with a list of IValues? The C++ constructor expects a c10::List<IVector>, i.e., a (GenericList), but this structure appears to be impossible to construct. Any form of syntax I’ve tried to create one of these list structures fails at compilation with a

static_assert(!std::is_same<T, IValue>::value, "This constructor is not valid for List<IValue>. Please use c10::impl::GenericList(elementType) instead.");

Using the recommended c10::impl implementation does not change anything.

I would expect a constructor for IValue to exist with a std::vector<IValue> signature, which is true for constructing an IValue from a tensor vector of type std::vector<Tensor>.

2

This question has been asked previously, but nobody seems to know how this structure works

3

Even basic stack allocations of these list structures fails. Neither of these statements will compile with the same uninformative error.

c10::impl::GenericList inputs;

c10::List<torch::IValue> inputs;
4

Hi,

I ran into the same issue when my model expected two lists of strings input via *args.

Using vector<vector> gave me the static assert.

Turned out that the inner list could not simply be vector but needed to be a Generic list which had to be initialized with the type.

In my case I solved it like that:

auto batch_1 = c10::impl::GenericList(c10::StringType::get());
batch_1.emplace_back("FOO");
auto batch_2 = c10::impl::GenericList(c10::StringType::get());
batch_2.emplace_back("BAR");

model.forward({batch_1, batch_2});

Hope that helps!