Generic dispatch with Symbols

问题:

I was wondering if there was a way to use Symbols for multiple dispatch, but also include a "catch-all method". i.e. something like

function dispatchtest{alg<:Symbol}(T::Type{Val{alg}})
  println("This is the generic dispatch. The algorithm is $alg")
end
function dispatchtest(T::Type{Val{:Euler}})
  println("This is for the Euler algorithm!")
end

The second one works and matches what's in the manual, I'm just wondering how you get the first one to work.

回答1:

You can do it this way:

julia> function dispatchtest{alg}(::Type{Val{alg}})
           println("This is the generic dispatch. The algorithm is $alg")
       end
dispatchtest (generic function with 1 method)

julia> dispatchtest(alg::Symbol) = dispatchtest(Val{alg})
dispatchtest (generic function with 2 methods)

julia> function dispatchtest(::Type{Val{:Euler}})
           println("This is for the Euler algorithm!")
       end
dispatchtest (generic function with 3 methods)

julia> dispatchtest(:Foo)
This is the generic dispatch. The algorithm is Foo

julia> dispatchtest(:Euler)
This is for the Euler algorithm!