UpdateIndex is a package to explore a method to get around the the problem I wrote about in JuliaLang/julia#15630.
The issue: In Julia, the command A[i] += s quickly gets lowered to A[i] = A[i] + s. For normal arrays this is fine but it is sometimes expensive to call A[i] and we would like to avoid that.
This package introduces the macro @update! that transforms the expression A[i...] ?= s where ? is some binary infix operator to the call updateindex!(A, ?, s, i...). The default fallback method for updateindex! is: updateindex!(A, f, s, I::Vararg) = A[I...] = f(A[I...], s) which will just do the same thing as if no macro would have been used.
A type that implements getindex and setindex! can now chose to implement updateindex! for faster updates.
As a proof of concept, this package implements updateindex! for scalar indexing into a sparse matrix.
julia> const A = sprand(10^4, 10^4, 0.01);
julia> A[1000, 1000] = 1
1
julia> @time for i in 1:10^5 # Normal way
A[1000, 1000] += 1
end
0.003079 seconds
julia> @time for i in 1:10^5 # With macro, almost 2x faster
@update! A[1000, 1000] += 1
end
0.001677 seconds