You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: expressions.rs
    path of file: ./repos/rust/examples
    
    the code of the file until where you have to start completion: extern crate rand;
extern crate tensorflow;

use std::error::Error;
use std::result::Result;
use tensorflow::expr:
    
fn main() -> Result<(), Box<dyn Error>> {
    // Build the graph
    let mut g = Graph::new();
    let y_node = {
        let mut compiler = Compiler::new(&mut g);
        let x_expr = <Placeholder<f32>>::new_expr(&vec![2], "x");
        compiler.compile(x_expr * 2.0f32 + 1.0f32)?
    };
    let x_node = g.operation_by_name_required("x")?;
    // This is another valid way to get x_node and y_node:
    // let (x_node, y_node) = {
    //   let mut compiler = Compiler::new(&mut g);
    //   let x_expr = <Placeholder<f32>>::new_expr(&vec![2], "x");
    //   let x_node = compiler.compile(x_expr.clone())?;
    //   let y_node = compiler.compile(x_expr * 2.0f32 + 1.0f32)?;
    //   (x_node, y_node)
    // };
    let options = SessionOptions::new();
    let session = Session::new(&options, &g)?;

    // Evaluate the graph.
    let mut x = <Tensor<f32>>::new(&[2]);
    x[0] = 2.0;
    x[1] = 3.0;
    let mut step = SessionRunArgs::new();
    step.add_feed(&x_node, 0, &x);
    let output_token = step.request_fetch(&y_node, 0);
    session.run(&mut step).unwrap();

    // Check our results.
    let output_tensor = step.fetch::<f32>(output_token)?;
    let mut checker = Checker::new(1e-3);
    checker.check("output_tensor[0]", 5.0, output_tensor[0]);
    checker.check("output_tensor[1]", 7.0, output_tensor[1]);
    checker.result()
}