Neat way of broadcasting getindex and getfield

General Usage
1

I often find myself wanting to broadcast getindex and getfield, which is perfectly doable, but could enjoy a nicer syntax. I figured out if I define the operator .. in the right way, I get a kind-of nice syntax for doing this without macros:

a = [randn(3) for _ in 1:4];
b = [complex(i,i+1) for i in 1:4];
(..)(x::AbstractArray,i...) = getindex.(x,i...)
(..)(x::AbstractArray,i::Symbol) = getfield.(x,i)

julia> a..2 == getindex.(a, 2)
true

julia> b..:re == getfield.(b, :re)
true

Edit: To broadcast getindex for dicts, the following method is useful

(..)(x::AbstractDict,i...) = getindex.(Ref(x), i...)
mydict..mykeys # now works
3 Likes
2

The problem with this approach is that it won’t fuse with other dot calls, so you may generate unnecessary loops and temporary arrays.

3

Yep, that is an issue. The cases where I do want to use this syntax tend to be casual scripting where ugly code is worse than the performance hit though. An alternative approach is to find a single-character operator that when prefixed with a . lowers to broadcast, such as

julia> Meta.@lower a.~b
:($(Expr(:thunk, CodeInfo(
    @ none within `top-level scope'
1 ─ %1 = Base.broadcasted(~, a, b)
│   %2 = Base.materialize(%1)
└──      return %2
))))

and define this operator to do regular getindex. Unfortunately, ... is already taken so it is not interpreted as broadcasting of the .. operator

4

Wow, this is very creative. One way to avoid generating temporary arrays is to use broadcasted:

using Base.Broadcast: broadcasted
(..)(x, i...) = broadcasted(getindex, x, i...)
(..)(x, i::Union{Symbol, String}) = broadcasted(getfield, x, i)

Although you have to write something like (a..2) .+ 1 and (b..:re) .+ 1. You also need to write identity.(a..2) or copy(a..2) to materialize it…

1 Like
5

What packages resp. community standards/solutions/notations do we currently have for broadcasted getindex on arrays of arrays (to do getindex on the inner arrays)? So, equivalents to broadcast(getindex, someAoA, Ref(some_idx_or_idx_range))?

I’m aware that the topic is under discussion as a language feature, but I’m curious which approaches are in use “in the wild” right now.