AnonymousEnums.jl

Enums without named instances.

The Base.@enum macro creates named instances for the subtypes of Enum. However, providing unique names for those instances can sometimes be problematic, especially when it comes to code generation.

To address these issues, some packages (such as EnumX.jl) offer alternatives to the Base.@enum macro. These alternatives involve implementing instances in a module.

This package takes it a step further by not naming the instances at all! The idea is that knowing the subtype of Enum should be sufficient to understand the values of an enum. Therefore, it should be possible to manipulate the instances using their symbols. Additionally, since the Julia compiler propagates constant symbols, no performance impact is expected.

Usage

The package provides the exported @anonymousenum macro for creating an Enum subtype. This macro can be used similarly to Base.@enum.

julia> @anonymousenum Fruit::UInt8 begin
           apple
           banana
       end
julia> apple = Fruit(:apple)
julia> @assert apple == Fruit(0)
julia> @assert apple == :apple
julia> @assert instances(Fruit) == (:apple, :banana)

Use case: Code generation

This package was developed to generate enums from type schemas while keeping the generated types and scopes as implementation details of the code generator.

Using this package allows generating an API like the following:

julia> writer.fruit.type = :apple
julia> if reader.fruit.type == :apple
           # do something
       elseif reader.fruit.type == :banana
           # do something else
       end

Note that in the example above, the symbols :apple and :banana are constant, enabling the same performance as traditional enums.