add Index[begin] on 1.4

Author: Michael Abbott

src/selectors.jl

@@ -70,3 +70,10 @@ Base.lastindex(::Type{Index}) = LastIndex()
 Index(::LastIndex) = LastIndex()
 
 findindex(sel::LastIndex, range::AbstractArray) = lastindex(range)
+
+if VERSION >= v"1.4" # same thing for Index[begin]
+    struct FirstIndex <: Selector{Int} end
+    Base.firstindex(::Type{Index}) = FirstIndex()
+    Index(::FirstIndex) = FirstIndex()
+    findindex(sel::FirstIndex, range::AbstractArray) = firstindex(range)
+end

test/_basic.jl

@@ -65,6 +65,9 @@ end
     @test V(Index[1]) == V[1]
     @test V(Index[2:3]) == V[2:3]
     @test V(Index[end]) == V[end]
+    if VERSION >= v"1.4"
+        @test V(Index[begin]) == V[1]
+    end
 
     V2 = wrapdims(rand(Int8, 5), [1,2,3,2,1])
     @test V2(==(2)) == V2[[2,4]]