Implement Iterators.reverse for MemoryView (#4)

src/basic.jl

@@ -191,3 +191,21 @@ function Base.reverse(mem::MemoryView)
     end
     cp
 end
+
+struct ReverseMemoryView{T}
+    # I can't think of a reason to allow mutable memory views here
+    mem::ImmutableMemoryView{T}
+end
+
+function Iterators.reverse(mem::MemoryView{T}) where {T}
+    ReverseMemoryView{T}(ImmutableMemoryView(mem))
+end
+Iterators.reverse(x::ReverseMemoryView) = x.mem
+
+Base.length(x::ReverseMemoryView) = length(x.mem)
+Base.eltype(::Type{ReverseMemoryView{T}}) where {T} = T
+
+function Base.iterate(x::ReverseMemoryView, state=length(x))
+    iszero(state) && return nothing
+    (@inbounds(x.mem[state]), state - 1)
+end

test/runtests.jl

@@ -81,9 +81,9 @@ end
     @test first(mem) == UInt8('a')
     @test last(mem) == UInt8('c')
 
-    memory = Memory{Float32}(undef, 6)
+    memory = Float32[0.1, -119.2, 150.3, Inf, -Inf]
     mem = MemoryView(memory)
-    @test all(i == j for (i, j) in zip(mem, memory))
+    @test all(i === j for (i, j) in zip(mem, memory))
     @test length(mem) == length(memory)
     @test mem == memory
 
@@ -399,6 +399,16 @@ end
     end
 end
 
+@testset "Iterators.reverse" begin
+    for v in Any[AbstractString["abc", "def", ""], Char['a', 'b'], UInt32[], Int16[9, 2, 1]]
+        mem = MemoryView(v)
+        it = Iterators.reverse(mem)
+        @test length(it) == length(mem)
+        @test collect(it) == reverse(mem)
+        @test Iterators.reverse(it) === ImmutableMemoryView(mem)
+    end
+end
+
 @testset "Equality" begin
     v = rand(UInt, 10)
     m1 = MemoryView(v)