micro_errors

Utilities to deal with errors without taking the derive macro approach.

Exposes a struct ErrorChain to typically be used within the Err variant of Result. ErrorChain contains a generic payload and a recusive struct, ErrorLink, which in turn contains either a summary message or a backtrace (intended to be of the last link). See below.

#[derive(Debug)]
pub struct ErrorChain<T: Display>(pub T, pub ErrorLink);

For the generic payload as String, utilities have been implemented to aid chaining (e.g., .map_err'ing).

Gist

Creating an ErrorChain from a non ErrorChain.

pub fn function_1() -> Result<(), ErrorChain<String>> {
    Err::<(), _>(std::io::Error::other("not an `ErrorChain`"))
        .map_err(ErrorChain::onboard_fn("that is ok"))
}

Creating an ErrorChain from an existing ErrorChain.

pub fn function_2() -> Result<(), ErrorChain<String>> {
    Err::<(), _>(ErrorChain::start("key glock"))
        .map_err(ErrorChain::add_fn("who I be"))
        .map_err(ErrorChain::add_fn("I dunno"))
}

Output of displaying/println!ing the error being something like below.

Error no. 0: I dunno
Error no. 1: who I be
Error no. 2: key glock
Approximate backtrace of error no. 2:
   0: micro_errors::ErrorLink::severed
             at ./src/lib.rs:58:23
   1: micro_errors::ErrorChain<alloc::string::String>::start
             at ./src/lib.rs:76:13
   2: micro_errors::test_crate
             at ./src/lib.rs:14:22
   3: micro_errors::test_crate::{{closure}}
             at ./src/lib.rs:4:16

Again, creating an ErrorChain from an existing ErrorChain.

#[allow(dead_code)]
#[derive(PartialEq)]
enum ErrorReasons {
    One,
    Two,
    Three
}
impl std::fmt::Display for ErrorReasons {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let as_string = match self {
            ErrorReasons::One => "one",
            ErrorReasons::Two => "two (easter egg)",
            ErrorReasons::Three => "three",
        }; 
        write!(f, "{}", as_string)
    }
}
pub fn function_3() -> Result<(), ErrorChain<String>> {
    match Err::<(), _>(ErrorChain(ErrorReasons::Two, ErrorLink::severed())) {
        Err(error_chain) if error_chain.0 == ErrorReasons::Two => println!("{}", error_chain),
        _ => panic!("look above"),
    }

    Err::<(), _>(ErrorChain(ErrorReasons::One, ErrorLink::severed()))
        .map_err(|e| ErrorChain::add("food", e))
}

micro_errors 0.2.4

micro_errors

Gist