Problem with @which source code number of lines?

KZiemian · November 3, 2018, 10:59pm

This topic is too deep in language for my, to understand what is really going on, so maybe I wrongly think that is a problem.

When you using

@which sum([1 2 3])

you get line sum(a::AbstractArray) in Base at reducedim.jl:645. This is great feature, especially when you use Jupyter, but this line is (probably) wrong. reducedim.jl:645 is inside for loop below any!(r, A) function and function sum(a::AbstractArray) is absent from this file. Function sum(A::AbstractArray; dims) is at the line 370 of this file.

Sukera · November 3, 2018, 11:06pm

No, this position is actually correct! sum is one of the functions in Base that are created using @eval, with a mechanism used to define function interfaces with the same signature but for different functions.

Take a look:

github.com

JuliaLang/julia/blob/0d713926f85dfa3e4e0962215b909b8e47e94f48/base/reducedim.jl#L641-L652


      
          for (fname, _fname, op) in [(:sum,     :_sum,     :add_sum), (:prod,    :_prod,    :mul_prod),
                                      (:maximum, :_maximum, :max),     (:minimum, :_minimum, :min)]
              @eval begin
                  # User-facing methods with keyword arguments
                  @inline ($fname)(a::AbstractArray; dims=:) = ($_fname)(a, dims)
                  @inline ($fname)(f::Callable, a::AbstractArray; dims=:) = ($_fname)(f, a, dims)
          
          
        # Underlying implementations using dispatch
                  ($_fname)(a, ::Colon) = ($_fname)(identity, a, :)
                  ($_fname)(f, a, ::Colon) = mapreduce(f, $op, a)
              end
          end

In this snippet, a loop is going over some fixed tuples in a list and creates a function with e.g. sum as the name and some method definitions with various arguments (in this example sum(a::AbstractArray; dims=:) = _sum(a, dims)). The definition in line 370 is just for documentation purposes (sort of like *.h files are used nowadays in C/C++ programming) - notice the docstring above the definition and the lack of a function body.

KZiemian · November 3, 2018, 11:19pm

Thank you for explaining that, now that make more sens to me. Can you also tell me why is one place is sum(A::AbstractArray; dims) and in other sum(A::AbstractArray)?