Behold

A simple library to aide in contextual debugging. This is a partial Rust port of the Python Behold library.

Core Concept

Sometimes print debugging is the best way to examine the state of a running program. But frequently you only care about the prints in a particular code path. With Behold, one part of the program can control debugging in another.

All Behold instances share the same global context to control what to print. However, a Behold instance can be created and configured to determine how or what it prints.

Contextual Debugging

BEHOLD.show("testing".to_string()) will print "testing" to the screen. BEHOLD.when(true).show("testing".to_string()) will print "testing" to the screen. BEHOLD.when(false).show("testing".to_string()) will do nothing. BEHOLD.when_context("key".to_string()).show("testing".to_string()) will print "testing" to the screen but only if the "testing" key has been set to true previously.

extern crate behold;

use behold::behold;

fn f(idx: usize) {
    behold().show(format!("Hello from f({})!", idx));
}

fn f2(idx: usize) {
    // Do something hard to debug
    behold().when(idx % 2 == 0).show(format!("Hello from f2({})!", idx));
}

fn f3(idx: usize) {
    // Do something hard to debug
    behold().when_context(format!("f3-{}", idx)).show(format!("Hello from f3({})!", idx));
}

fn main() {
    for i in 0..3 {
        println!("\n");
        f(i);
        f2(i);
        f3(i);
        // Context is global
        behold().set_context("f3-1".to_string(), true);
    }
}

Produces the output:

Behold: Hello from f(0)!
Behold: Hello from f2(0)!


Behold: Hello from f(1)!
Behold: Hello from f3(1)!


Behold: Hello from f(2)!
Behold: Hello from f2(2)!

Tagged Printing

Each instance of Behold can be configured with a tag to help distinguish output.

extern crate behold;

use behold::behold;

fn main() {
    behold().tag("yolo".to_string()).show("Hello world!".to_string());
}

Produces the output:

Hello world!, yolo