Macro throwing::define_error

define_error!() { /* proc-macro */ }

Creates a new composite error type with a given name.

This macro works almost exactly like #[throws], except that it isn’t attached to a function.

Since there is no way to infer a name for the type, it must be specified explicitly with type SomeError = .... Unlike #[throws], this macro also accepts a visibility declaration, since it cannot be copied from the function.

Examples

// Defines an error with a single variant
// ParseIntListError will implement From<ParseIntError>.
define_error!(type ParseIntListError = ParseIntError);

// Defines an error with a multiple variants
define_error!(type DownloadFileError = HttpError | io::Error);

// Defines an error with a suberror
// DownloadDirError will implement From<DownloadFileError>.
define_error!(type DownloadDirError = HttpError | io::Error | ZipError | break DownloadFileError);

// Defines a public error
define_error!(pub type PublicError = io::Error);

// Defines a error crate-wide error
define_error!(pub(crate) type CrateWideError = io::Error);

pub struct Id(u64);
 
define_error!(pub type ParseIdError = ParseIntError);
 
impl FromStr for Id {
    type Err = ParseIdError;
     
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let value = s.parse()?;
        Ok(value)
    }
}