Simple transformer

I’m trying to create a simple transformer.
Why can’t this code work I get an error here

// Define the Transformer model

#include <torch/torch.h>
struct TransformerModel : torch::nn::Module
    TransformerModel(int input_size, int num_heads, int num_layers, int hidden_dim)
        // Define the input and output embeddings
        embed = register_module("embed", torch::nn::Linear(input_size, hidden_dim));

        // Create a multi-head self-attention layer
        self_attn = register_module("self_attn", torch::nn::MultiheadAttention(hidden_dim, num_heads));

        // Create a feedforward neural network
        feedforward = register_module("feedforward", torch::nn::Sequential(
                                                         torch::nn::Linear(hidden_dim, hidden_dim),
                                                         torch::nn::Linear(hidden_dim, hidden_dim)));

        // Create the transformer layers
        transformer_layers = register_module("transformer_layers", torch::nn::TransformerEncoderLayer(hidden_dim, num_heads));

        // Create the transformer encoder
        transformer_encoder = register_module("transformer_encoder", torch::nn::TransformerEncoder(transformer_layers, num_layers));

        // Define the output layer
        output_layer = register_module("output_layer", torch::nn::Linear(hidden_dim, 1));

    torch::Tensor forward(torch::Tensor x)
        // Embed the input data
        x = embed->forward(x);

        // Perform multi-head self-attention
       //ERROR IS HERE
///(38,9): error C2679: binary '=': no operator found which takes a right-hand operand of type 'std::tuple<at::Tensor,at::Tensor>' (or there is no acceptable conversion) 
        x = self_attn->forward(x, x, x);

        // Apply feedforward network
        x = feedforward->forward(x);

        // Apply the transformer encoder
        x = transformer_encoder->forward(x);

        // Apply the output layer
        x = output_layer->forward(x);

        return x;

    torch::nn::Linear embed{nullptr};
    torch::nn::MultiheadAttention self_attn = nullptr;

    torch::nn::Sequential feedforward{nullptr};
    torch::nn::TransformerEncoderLayer transformer_layers{nullptr};
    torch::nn::TransformerEncoder transformer_encoder{nullptr};
    torch::nn::Linear output_layer{nullptr};

Thanks in advance