display_with_options

This tiny (< 200 LOC) crate allows you to pass options around in Display and Debug.

It also adds a way to indent a formatter implicitly on fresh new lines.

Both components are technically separate, but interact in useful ways to provide a customizable indentation and pretty printing pipeline. In contrast to similar crates, this one gives you full control while maintaining a close relationship with rust core functionality.

Usage Examples

IndentingFormatter

use display_with_options::IndentingFormatter;

fn main() {
    let mut dst: Vec<u8> = vec![];
    
    writeln!(dst, "A").unwrap();
    
    let mut f = IndentingFormatter::new(&mut dst, "    ");
    writeln!(f, "B").unwrap();
}

Result:

A
    B

DisplayWithOptions

use std::fmt::{Formatter, Write};
use display_with_options::{DisplayWithOptions, IndentingFormatter, IndentOptions, with_options};

/// Tree-like structure
struct Node {
    name: String,
    children: Vec<Box<Node>>
}

impl Node {
    pub fn new(name: &str, children: Vec<Box<Node>>) -> Box<Node> {
        Box::new(Node {
            name: name.to_string(),
            children
        })
    }
}

impl<'a> DisplayWithOptions<IndentOptions<'a>> for Node {
    fn fmt(&self, f: &mut Formatter, options: &IndentOptions) -> std::fmt::Result {
        writeln!(f, "{}{}", options, self.name)?;

        let options = options.deeper();
        let mut f = IndentingFormatter::new(f, &options.full_indentation);
        let options = options.restart();

        for child in self.children.iter() {
            write!(f, "{}", with_options(child.as_ref(), &options))?;
        }

        Ok(())
    }
}

// Test the Code

fn main() {
    let tree = Node::new("A", vec![
        Node::new("B", vec![
            Node::new("C", vec![]),
        ]),
        Node::new("D", vec![]),
    ]);

    let options = IndentOptions::new("    ");
    println!("{}", with_options(tree.as_ref(), &options));
}

Result:

A
    B
        C
    D