InstanceDispatch

InstanceDispatch.jl is a single-macro package to mix enumerations (or anything that defines a method for Base.instances) and dispatch-on-value in Julia.

Simply put it allows using dispatching in a type-stable fashion by writing code such as:

using InstanceDispatch

@enum GreetEnum Hello Goodbye

function greet(::Val{Hello}, who)
    return "Hello " * who
end
function greet(::Val{Goodbye}, who)
    return "Goodbye " * who
end
@instancedispatch greet(::GreetEnum, who)

This last line is equivalent to defining the following method:

function greet(e::GreetEnum, who)
    if e == Hello
        return greet(Val(Hello), who)
    elseif e == Goodbye
        return greet(Val(Goodbye), who)
    else
    end
end

This avoids the performance pit that you would encounter in simply writing:

function greet(e::GreetEnum, who)
    return greet(Val(e), who)
end

Installation

import Pkg; Pkg.add("InstanceDispatch")

Alternatives

• ValSplit.jl essentially performs the same task for Symbol-based value type dispatch.