Prevent mapslices from mutating the original array

Author: timholy

base/abstractarray.jl

@@ -1417,7 +1417,8 @@ function mapslices(f, A::AbstractArray, dims::AbstractVector)
         idx[d] = Colon()
     end
 
-    r1 = f(view(A, idx...))
+    Aslice = A[idx...]
+    r1 = f(Aslice)
 
     # determine result size and allocate
     Rsize = copy(dimsA)
@@ -1449,7 +1450,8 @@ function mapslices(f, A::AbstractArray, dims::AbstractVector)
             for i in 1:nidx
                 idx[otherdims[i]] = ridx[otherdims[i]] = I.I[i]
             end
-            R[ridx...] = f(view(A, idx...))
+            _unsafe_getindex!(Aslice, A, idx...)
+            R[ridx...] = f(Aslice)
         end
     end
 

test/arrayops.jl

@@ -843,6 +843,12 @@ let
     n3a = mapslices(x-> ones(1,6), c, [2,3])
     @test size(n1a) == (1,6,4) && size(n2a) == (1,3,6)  && size(n3a) == (2,1,6)
     @test size(n1) == (6,1,4) && size(n2) == (6,3,1)  && size(n3) == (2,6,1)
+
+    # mutating functions
+    o = ones(3, 4)
+    m = mapslices(x->fill!(x, 0), o, 2)
+    @test m == zeros(3, 4)
+    @test o == ones(3, 4)
 end