is_default 1.0.0

A unified API for checking if a value is default, with easy derive support for custom types.

Example, instead of is_none for Option and is_empty for Vec can be used is_default for all.

assert!(None::<u8>.is_none());
assert!(Vec::<u8>::new().is_empty());

use is_default::IsDefault;
assert!(None::<u8>.is_default());
assert!(Vec::<u8>::new().is_default());

The IsDefault trait is implemented for most standard types. With the derive feature, you can easily generate implementations for your own types:

Derive

To use derive macro add dependency with the feature derive in Cargo.toml:

is_default = { version = "1", features = ["derive"] }

Structs

A struct can derive IsDefault if all its fields implement IsDefault.

use is_default::IsDefault;

#[derive(IsDefault)]
struct Unit;
assert!(Unit.is_default());

#[derive(IsDefault)]
struct Wrapper(u8);
assert!(Wrapper(0).is_default());
assert!(!Wrapper(1).is_default());

#[derive(IsDefault)]
struct Point { x: i16, y: f32 }
assert!(Point{ x: 0, y: 0.0 }.is_default());
assert!(!Point{ x: 1, y: 0.0 }.is_default());
assert!(!Point{ x: 0, y: 0.1 }.is_default());

Enums

Enums can derive IsDefault using the #[is_default] or #[default] attribute. This allows deriving both Default and IsDefault using the same attribute.

use is_default::IsDefault;

#[derive(IsDefault)]
enum X {
    A,
    #[is_default]
    B,
}
assert!(X::B.is_default());
assert!(!X::A.is_default());

#[derive(IsDefault)]
enum Y {
    #[default]
    A,
    B,
}
assert!(Y::A.is_default());
assert!(!Y::B.is_default());

#[derive(Default, IsDefault)]
enum Z {
    A,
    #[default]
    B,
}
assert!(Z::B.is_default());
assert!(!Z::A.is_default());
assert!(matches!(Z::default(), Z::B));