Allow broadcasting All and Between (#10)

Author: nalimilan

src/DataAPI.jl

@@ -169,6 +169,34 @@ struct Cols{T<:Tuple}
     Cols(args...) = new{typeof(args)}(args)
 end
 
+"""
+    BroadcastedSelector(selector)
+
+Wrapper type around a `Between`, `All` or `Cols` indicating that
+an operation should be applied to each column included by the wrapped selector.
+
+# Examples
+```jldoctest
+julia> using DataAPI
+
+julia> DataAPI.Between(:a, :e) .=> sin
+DataAPI.BroadcastedSelector{DataAPI.Between{Symbol, Symbol}}(DataAPI.Between{Symbol, Symbol}(:a, :e)) => sin
+
+julia> DataAPI.Cols(r"x") .=> [sum, prod]
+2-element Vector{Pair{DataAPI.BroadcastedSelector{DataAPI.Cols{Tuple{Regex}}}, _A} where _A}:
+ DataAPI.BroadcastedSelector{DataAPI.Cols{Tuple{Regex}}}(DataAPI.Cols{Tuple{Regex}}((r"x",))) => sum
+ DataAPI.BroadcastedSelector{DataAPI.Cols{Tuple{Regex}}}(DataAPI.Cols{Tuple{Regex}}((r"x",))) => prod
+```
+"""
+struct BroadcastedSelector{T}
+    sel::T
+    BroadcastedSelector(sel) = new{typeof(sel)}(sel)
+end
+
+Base.Broadcast.broadcastable(x::Between) = Ref(BroadcastedSelector(x))
+Base.Broadcast.broadcastable(x::All) = Ref(BroadcastedSelector(x))
+Base.Broadcast.broadcastable(x::Cols) = Ref(BroadcastedSelector(x))
+
 """
     unwrap(x)
 

test/runtests.jl

@@ -63,6 +63,11 @@ end
         b = DataAPI.Between(x, y)
         @test b.first == (x isa Int ? x : Symbol(x))
         @test b.last == (y isa Int ? y : Symbol(y))
+
+        @test (b .=> sum) ===
+            (DataAPI.BroadcastedSelector(DataAPI.Between(x, y)) => sum)
+        @test (b .=> [sum, float]) ==
+            (Ref(DataAPI.BroadcastedSelector(DataAPI.Between(x, y))) .=> [sum, float])
     end
 
     @test_throws MethodError DataAPI.Between(true, 1)
@@ -81,6 +86,15 @@ end
         @test length(a.cols) == 1
         @test a.cols[1] isa v
         @test a.cols[1].cols == ()
+
+        @test (v() .=> sum) ===
+            (DataAPI.BroadcastedSelector(v()) => sum)
+        @test (v(:a) .=> sum) ===
+            (DataAPI.BroadcastedSelector(v(:a)) => sum)
+        @test (v((1,2,3), :b) .=> sum) ===
+            (DataAPI.BroadcastedSelector(v((1,2,3), :b)) => sum)
+        @test (v() .=> [sum, float]) ==
+            (Ref(DataAPI.BroadcastedSelector(v())) .=> [sum, float])
     end
 
 end