This is by far the simplest way of creating the code. We define the types that Shape can take:

impl Calculate<i32> for Shape<i32> 
{ 
  fn calc(&self) -> i32
  {
    self.line_one * 2 + self.line_two * 2 
  }
}

Writing the code like this ensures that we cannot pass anything into the implementations that don't make any sense (for example, types that cannot have + or * applied to them).