Macro impl_error_from

macro_rules! impl_error_from {
    ($thing:ty, $from_thing:ty, $field:ident) => { ... };
}

Implements the From trait for converting a specific type into an enum variant or struct field.

This macro is useful when building error enums or wrapper types that need to support automatic conversions from underlying error types using the ? operator.

Parameters

• $thing: The target type to implement From for (usually an enum or struct).
• $from_thing: The source type that should be converted into $thing.
• $field: The variant or field of $thing that wraps a value of type $from_thing.

Example

enum MyError {
    Io(std::io::Error),
    Parse(std::num::ParseIntError),
}

impl_error_from!(MyError, std::io::Error, Io);
impl_error_from!(MyError, std::num::ParseIntError, Parse);

fn parse_number(s: &str) -> Result<i32, MyError> {
    let n: i32 = s.parse()?; // Automatically converts ParseIntError into MyError
    Ok(n)
}