1 unstable release
0.1.0 | May 11, 2020 |
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#1937 in Rust patterns
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newtype-enum
Traits and macro to use newtype enums and convert between enums and their variants.
A newtype enum is an enum where every variant wraps another type and the wrapped type can uniquely identify the variant.
You can use the newtype_enum
attribute macro to define a newtype enum. When the macro is applied to an enum E
it will implement the Enum
trait for E
and the Variant<E>
trait for all variant types.
See the examples in the Enum
trait for usage of the available methods.
The macro will also convert all unit and struct variants to generated structs and replace the enum variant with a newtype variant that contains the generated struct. See below for the rules and options that are available.
Variant transformation
The variants of the enum will be converted in the following way:
Unit variants
#[newtype_enum]
enum Test {
Example,
}
enum Test {
Example(Test_variants::Example),
}
mod Test_variants {
pub(super) struct Example;
}
Newtype variants
#[newtype_enum]
enum Test {
Example(usize),
}
enum Test {
Example(usize),
}
Struct variants
#[newtype_enum]
enum Test {
Example { test: usize },
}
enum Test {
Example(Test_variants::Example),
}
mod Test_variants {
pub(super) struct Example {
pub(super) test: usize,
}
}
Attribute arguments
You can pass the following arguments to the newtype_enum
macro:
Variants module name
#[newtype_enum(variants = "test")]
enum Test {
Example,
}
enum Test {
Example(test::Example),
}
mod test {
// <-- the name of the generated module
pub(super) struct Example;
}
Variants module visibility
#[newtype_enum(variants = "pub(crate) test")]
enum Test {
Example,
}
enum Test {
Example(test::Example),
}
pub(crate) mod test {
// <-- the visibility of the generated module
pub(super) struct Example;
}
Visibilities and attributes (e.g. #[derive]
attributes)
The visibility of the generated variant structs behaves as if they where part of a normal enum: All variants and their fields have the same visibiltiy scope as the enum itself.
Attributes will be passed to the following locations:
Location | Destination |
---|---|
enum | Enum and generated variant structs |
enum variant | Generated variant struct |
variant field | Generated struct field |
#[newtype_enum]
#[derive(Debug)]
pub(crate) enum Test {
#[derive(Clone)]
Example {
test: usize,
pub(super) test_super: usize,
pub(self) test_self: usize,
},
}
#[derive(Debug)]
pub(crate) enum Test {
Example(Test_variants::Example),
}
pub(crate) mod Test_variants {
#[derive(Debug, Clone)]
pub(crate) struct Example {
pub(crate) test: usize,
pub(in super::super) test_super: usize,
pub(super) test_self: usize,
}
}
License
Licensed under either of
- Apache License, Version 2.0, (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT)
at your option.
Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.
Dependencies
~2MB
~43K SLoC