Currently, Tera::render returns a string, which comes from Renderer::render, which builds the string by rendering each component and then using String::push_str.

Unfortunately for extremely large templates, this uses a lot of memory and might take a lot of time, and the biggest problem is that rendering is a blocking operation. It might be smarter to have a different render method that returns a struct that implements std::io::Read so it can be streamed and not store the entire response in the heap before sending it over to the server.

(I'm obviously talking about using tera in conjunction with a web application framework as opposed to tera alone, but let's be honest, that's 99% of tera's use cases)