You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: mod.rs
    path of file: ./repos/smartcore/src/error
    
    the code of the file until where you have to start completion: //! # Custom warnings and errors
use std::error::Error;
use std::fmt;

#[cfg(feature = "serde")]
use serde::{Deserialize, Serialize};

/// Generic error to be raised when something goes wrong.
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
#[derive(Debug)]
pub struct Failed {
    err: FailedError,
    msg: String,
}


    
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let failed_err_str = match self {
            FailedError::FitFailed => "Fit failed",
            FailedError::PredictFailed => "Predict failed",
            FailedError::TransformFailed => "Transform failed",
            FailedError::FindFailed => "Find failed",
            FailedError::DecompositionFailed => "Decomposition failed",
            FailedError::SolutionFailed => "Can't find solution",
            FailedError::ParametersError => "Error in input, check parameters",
            FailedError::InvalidStateError => "Invalid state, this should never happen", // useful in development phase of lib
        };
        write!(f, "{failed_err_str}")
    }