Keyword arguments is causing allocations

General Usage
1

Hi!

I am getting an allocation when using a keyword in the following MWE:

julia> function teste(a::AbstractVector{T}; b::Integer = 0, c::Integer = 0) where T
       return a[1] + b + c
       end
teste (generic function with 1 method)

julia> data = [1,2,3]
3-element Array{Int64,1}:
 1
 2
 3

julia> teste(data); @time teste(data)
  0.000003 seconds
1

julia> teste(data, b = 1); @time teste(data, b = 1)
  0.000002 seconds (1 allocation: 16 bytes)
2

julia> teste(data, c = 1); @time teste(data, c = 1)
  0.000002 seconds (1 allocation: 16 bytes)
2

julia> teste(data, b = 1, c = 1); @time teste(data, b = 1, c = 1)
  0.000002 seconds (1 allocation: 32 bytes)
3

Is it expected? Why calling a function using a keyword argument do an allocation?

By the way, if a is an Interger instead of a Vector, then I see no allocation at all.

2

I guess it is calling a specialised functions and for the case of only parameter a there is no operation to be performed.

Maybe check the generated code with @code_native

3

I am seeing this very same problem in a more complex function. If keywords are passed, then I have 1 allocation. Otherwise, I have no allocation.

4

Use BenchmarkTools.jl for this kind of microbenchmark.
You may just be seeing the result of accessing the global object data.

2 Likes
5

Nice! BenchmarkTools.jl shows that no allocation is performed in any of the cases. Thanks :smiley:

1 Like