问题
I just started learning Rust, and I'm making some small tools to help me understand the language. I have a problem formatting a String using the format! macro. As format! takes a literal, I am not able pass my string to it. I want to do this to dynamically add strings into the current string for use in a view engine. I'm open for suggestions if there might be a better way to do it.
let test = String::from("Test: {}");
let test2 = String::from("Not working!");
println!(test, test2);
What I actually want to achieve is the below example, where main.html contains {content}.
use std::io::prelude::*;
use std::fs::File;
use std::io;
fn main() {
let mut buffer = String::new();
read_from_file_using_try(&mut buffer);
println!(&buffer, content="content");
}
fn read_from_file_using_try(buffer: &mut String) -> Result<(), io::Error> {
let mut file = try!(File::open("main.html"));
try!(file.read_to_string(buffer));
Ok(())
}
So I want to print the contents of main.html after I formatted it.
回答1:
Short answer: it cannot be done.
Long answer: the format! macro (and its derivatives) requires a string literal, that is a string known at compilation-time. In exchange for this requirement, if the arguments provided do not match the format, a compilation error is raised.
What you are looking for is known as a template engine. A non-exhaustive list of Rust template engines in no particular order:
- Handlebars
- Rustache
- Maud
- Horrorshow
- fomat-macros
- ...
Template engines have different characteristics, and notably differ by the degree of validation occurring at compile-time or run-time and their flexibility (I seem to recall that Maud was very HTML-centric, for example). It's up to you to find the one most fitting for your use case.
回答2:
Check out the strfmt library, it is the closest I've found to do dynamic string formatting.
来源：https://stackoverflow.com/questions/32572486/how-can-i-use-a-dynamic-format-string-with-the-format-macro