icecream-rs

Print debugging with inspection for Rust, inspired by icecream for Python.

I tend to use a lot of print debugging when writing Rust. icecream provides the ic!() and ice!() macros to make print debugging more convenient, by formatting print statements with helpful information like:

• line number

• calling function

• module name

• file name

Debugging with ic!()

// src/example.rs
#[macro_use]
extern crate icecream;

mod a_module {
    fn some_function() {
        let x = Some(99);
        ic!();
        ic!(x);
        ic!(x.unwrap() + 1);
        ice!();
    }
}

Plain

ic!() prints the filename and line number.

example.rs:8 ❯

Matching on an identifier

ic!(x) prints the name of the variable and the value formatted with std::fmt::Debug.

example.rs:9 ❯ x = Some(99)

Matching on an expression

ic!(x.unwrap() + 1) evaluates the inner expression and prints the resulting value.

example.rs:10 ❯ x.unwrap() + 1 = 100

Printing more information

ice!() prints a longer output that includes the calling module and function.

example.rs::a_module::some_function:11 ❯

Configuring ic!()

You can also configure the characters used for symbols in the print output.

// main.rs
#[macro_use]
extern crate icecream;

fn main() {
    icecream::set_equals_symbol(" -> ");
    let x = 1;
    ic!(x);
}

main.rs:7 ❯ x -> 1

Tests

Tests must be run single-threaded with the --nocapture flag.

RUST_TEST_THREADS=1 cargo test -- --nocapture