While Julia is indeed a dynamically typed language, it also supports type annotations and can in most cases infer the static type of a variable. If you write a function

  function foo(x)
    #do something
  end

and you call foo(10) and foo("some string"), then the compiler will create specialized methods foo(x::Int) and foo(x::String). Then there is no need for tracking the dynamic type of x inside these functions.