Derive Macro amplify_derive::From

#[derive(From)]
{
    // Attributes available to this derive:
    #[from]
}

Implements From trait for the whole entity and/or its separate fields. Works well with #[derive(Error)] and, in many cases may require Default implementation (for details, pls see Examples below)

Examples

#[derive(From, Default)]
#[from(::std::io::Error)]
// Structure may contain no parameters
pub struct IoErrorUnit;

#[derive(From, Default)]
#[from(::std::io::Error)] // When no explicit binding is given, structure must implement `Default`
pub struct IoError {
    details: String,

    #[from]
    kind: IoErrorUnit,
}

#[derive(From)]
pub enum Error {
    // You can specify multiple conversions with separate attributes
    #[from(::std::io::Error)]
    #[from(IoError)]
    Io,

    #[from]
    Format(::std::fmt::Error),

    #[from]
    WithFields { details: ::std::str::Utf8Error },

    MultipleFields {
        // ...and you can also covert error type
        #[from(IoErrorUnit)]
        // rest of parameters must implement `Default`
        io: IoError,
        details: String,
    },
}

#[derive(Clone, Copy, PartialEq, Eq, Hash, Default, Debug, From)]
pub struct Wrapper(u32, i16);

If you use rust nightly and #![feature(never_type)] for [!], you can even do the following:

#![feature(never_type)]

#[macro_use]
extern crate amplify_derive;

#[derive(From)]
pub enum Error {
    // ... other error types
    #[from(!)]
    NeverType,
}