Rust: Error Handling with Custom Types

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Error handling is a vital component in any programming paradigm. Rust, being a systems programming language, places a significant emphasis on robust and type-safe error handling. In this article, we’ll explore how to define custom error types in Rust and handle them in idiomatic ways.

Defining Custom Errors

Rust provides the std::error::Error trait, which can be implemented for types that you want to use as errors. By convention, Rust errors also implement the Display trait for human-readable error messages.

In the provided code, we have two custom error types: FileError and ParseError.

#[derive(Debug)]
enum FileError {
    NotFound,
    PermissionDenied,
}

impl Display for FileError {
    fn fmt(&self, f: &mut Formatter) -> std::fmt::Result {
        match self {
            FileError::NotFound => write!(f, "File not found"),
            FileError::PermissionDenied => write!(f, "Permission denied"),
        }
    }
}

impl std::error::Error for FileError {}

The FileError type is an enumeration with two variants: NotFound and PermissionDenied. Implementing the Display trait allows us to provide a custom string representation for each variant. We also implement the Error trait for FileError, signaling that it can be used as an error type.