Can Julia functions match a specific symbol?

Question

Can Julia functions match a specific symbol rather than just a type Symbol? For example:

function test(x::Symbol(:ALPHA)) end
function test(x::Symbol(:BETA)) end

The above is what I was trying to accomplish, though the syntax is wrong.

are you about pattern matching? No, it not implement in Julia, but you can look on this: github.com/toivoh/julia-pattern-dispatch and this matchjl.readthedocs.io/en/latest — user4651282
See docs.julialang.org/en/latest/manual/performance-tips/… (though I agree, you may need it in your case). — Andy Hayden

Fengyang Wang Fengyang Wang · Accepted Answer · 2016-06-06T03:33:14

Do you really want an additional version of the function to be compiled for each symbol? An additional compilation is quite expensive, and the compiler will have to put in a branch anyway... you will not gain any performance by dispatching on the value.

Instead, you should probably write code like this:

function test(x::Symbol)
    if x == :ALPHA
         ...
    elseif x == :BETA
         ...
    else
         throw(ArgumentError("Expected :ALPHA or :BETA"))
    end
end

or if you don't like how this looks, consider using pattern matching with Match.jl:

test(x::Symbol) = @match x begin
    :ALPHA => ...
    :BETA  => ...
    _      => throw(ArgumentError("Expected :ALPHA or :BETA"))
end

If you really need dispatch, you can use a type to wrap around the value, like Val{:ALPHA}. This type needs to be created at the caller site. In 99% of situations, this is a bad idea. Remember that this does not prevent the branch when calling the function, and in fact makes it slower since dispatch is more expensive than a branch.

Can Julia functions match a specific symbol?

1 Answers