What #[derive(TryFrom)] generates

Derive TryFrom allows you to convert enum discriminants into their corresponding variants.

Enums

By default, a TryFrom<isize> is generated, matching the type of the discriminant. The type can be changed with a #[repr(u/i*)] attribute, e.g., #[repr(u8)] or #[repr(i32)]. Only field-less variants can be constructed from their variant, therefore the TryFrom implementation will return an error for a discriminant representing a variant with fields.

# use derive_more::TryFrom;
#
#[derive(TryFrom, Debug, PartialEq)]
#[try_from(repr)]
#[repr(u32)]
enum Enum {
    ImplicitZero,
    ExplicitFive = 5,
    FieldSix(usize),
    EmptySeven{},
}

assert_eq!(Enum::ImplicitZero, Enum::try_from(0).unwrap());
assert_eq!(Enum::ExplicitFive, Enum::try_from(5).unwrap());
assert_eq!(Enum::EmptySeven{}, Enum::try_from(7).unwrap());

// Variants with fields are not supported, as the value for their fields would be undefined.
assert!(Enum::try_from(6).is_err());