EnumOptionSet

@EnumOptionSet is a Swift attached member macro to declare option sets using an enumeration notation.

Purpose

The built-in OptionSet declaration syntax in Swift is quite cumbersome and repetitive:

struct ShippingOptions: OptionSet {
    let rawValue: Int

    static let nextDay = Self(rawValue: 1 << 0)
    static let secondDay = Self(rawValue: 1 << 1)
    static let priority = Self(rawValue: 1 << 2)
    static let standard = Self(rawValue: 1 << 3)

    static let all: Self = [.nextDay, .secondDay, .priority, .standard]
}

The same option set can be declared with the @EnumOptionSet macro and the enum like this:

@EnumOptionSet
enum ShippingOption {
    case nextDay, secondDay, priority, standard
}

[!NOTE] The macro generates a nested Set structure that conforms to the OptionSet protocol, using Int as the default raw value type and extracting options from the names of enum cases in the order of declaration.
It also generates the all property as an option composition, along with some other helper structure members.

Then you can create a typealias, and extend the option set with additional composite options:

typealias ShippingOptions = ShippingOption.Set
extension ShippingOptions {
    static let express: Self = [nextDay, secondDay]
}

Advanced usage

The macro also supports custom raw value types and indices:

@EnumOptionSet<UInt8>       // OptionSet.RawValue = UInt8
enum ShippingOption: Int {
    case nextDay            // Starting with index 0.       (rawValue: 1 << 0)
    case secondDay          // Incrementing by 1.           (rawValue: 1 << 1)
    case priority = 3       // Skipping index 2.            (rawValue: 1 << 3)
    case standard           // Continuing to increment.     (rawValue: 1 << 4)
}

[!TIP] The OptionSet.RawValue type can also be declared as the macro's first argument @EnumOptionSet(UInt8.self).
Currently, an even shorter form @EnumOptionSet(UInt8) works, but this may be a bug of the Swift syntax analyzer, so use it at your own risk.

[!NOTE] Enum raw values that are expressed in ways other than integer literals, as well as associated values, are ignored.
The enum's RawValue can be declared as an arbitrary type or omitted, conformance to CaseIterable is also not required.

Another significant advantage of the macro is that it provides additional safety checks not found in the built-in declaration.
Specifically, it performs checks for duplicate indices and raw value overflow. At compile-time, the macro determines the raw value bitset size based on the type name, and at runtime, it adds an assertion using the bitWidth property of the FixedWidthInteger raw value type.

Both of checks can be disabled with the checkOverflow attribute flag:

@EnumOptionSet<UInt8>(checkOverflow: false)
enum ShippingOption: Int {
    case nextDay, secondDay, priority, standard = 8 // Option bit index 8 is out of range for 'UInt8'.
}

[!NOTE] When overflow is ignored, raw values that exceed the type's capacity are set to zero, thereby excluding the corresponding options from the set.

Other goodies

Description

The macro generates easy to read description and debugDescription properties:

ShippingOptions.express.description // "[nextDay, secondDay]"

ShippingOptions.express.debugDescription // "OptionSet(0b00000011)"

The CustomStringConvertible and CustomDebugStringConvertible protocol conformance can be disabled by setting the generateDescription attribute flag to false.

Cases

The OptionSet maintains a connection to the enum through the cases property and initializer:

let shippingOptions = ShippingOptions(cases: [.secondDay, .priority])
shippingOptions.cases // [ShippingOption.secondDay, ShippingOption.priority]

These structure members are not generated for enums with associated values.

Subscript

The macro contains an OptionSet extension for accessing options as boolean flags using subscript notation:

var shippingOptions: ShippingOptions = []
shippingOptions[.standard] = true
shippingOptions[.express].toggle()
shippingOptions[.priority] = shippingOptions[.standard]
shippingOptions == .all // true

There are also multiple format checks and syntax fix suggestions.

The macro code is fully covered by unit tests.

Installation

To add the package to your Xcode project, open File -> Add Package Dependencies... and search for the URL:

https://github.com/DnV1eX/EnumOptionSet.git

Then, simply import EnumOptionSet and add the @EnumOptionSet attribute before the target enum.

[!WARNING] Xcode may ask to Trust & Enable the macro on first use or after an update.

References

• Proposal for adding a variant of this macro to the standard library (it never happened) with detailed discussion: [Pitch] @OptionSet macro.

[!IMPORTANT] I hope you enjoy the project and find it useful. Please bookmark it with ⭐️ and feel free to share your feedback. Thank you!

Also try @EnumRawValues - a Swift macro that enables full-fledged raw values for enumerations.

License

Copyright © 2024 DnV1eX. All rights reserved. Licensed under the Apache License, Version 2.0.