The branch on the first version will be eliminated. The second version is
far more idiomatic, however. Consider that the second version is trivially
extensible to more types while the first version cannot be extended at all.
On Tuesday, September 29, 2015, Matt <matthewn...@gmail.com> wrote:
> I want to write a method that is very similar between two types, with
> slight divergences. I'd like to write it avoiding code duplication.
>
> To take a simple example, let's say that the two types are Vector and
> Matrix. The method must print "I'm an array" for the two types, and then
> prints "I'm a vector" if the object is a vector, "I'm a matrix" if the
> object is a matrix.
>
> One way write this method is to use a "run time" dispatch
>
> function f{T, N}(x::Array{T, N})
> println("I'm an array")
> if N == 1
> println("I'm a vector")
> elseif N == 2
> println("I'm a matrix")
> end
> end
> f2(rand(10, 10))
> @code_warntype f2(rand(10, 10))
>
> A way to dispatch at compile time is to define as many auxiliary function
> as there are differing lines
>
> function _ansfunction(x::Vector)
> println("I'm a vector")
> end
> function _ansfunction(x::Matrix)
> println("I'm a matrix")
> end
> function f1(x)
> println("I'm an array")
> _ansfunction(x)
> end
> f1(rand(10, 10))
> @code_warntype f1(rand(10, 10))
>
> Another solution would be to iterate through two NTuples, where N is the
> number of differing lines
>
> for (t, x) in ((:Vector, :(println("I'm a vector"))),
> (:Matrix, :(println("I'm a Matrix"))))
> @eval begin
> function f2(x::$t)
> println("I'm an array")
> $x
> end
> end
> end
> f2(rand(10, 10))
> @code_warntype f2(rand(10, 10))
>
>
> These two last solutions work, but I really prefer the syntax of first
> solution : it allows to write the differing lines exactly at the place
> they're needed, when they're needed. It really starts to mattes when there
> are a few differing lines. Is there a syntax as clear as the first
> solution, but that "branch" at compile time?
>
