Make accumulate! compatible with offset indices

Plus add relevant tests

Author: Andy Ferris

base/accumulate.jl

@@ -383,12 +383,15 @@ function _accumulate1!(op, B, v1, A::AbstractVector, dim::Integer)
     inds = LinearIndices(A)
     inds == LinearIndices(B) || throw(DimensionMismatch("LinearIndices of A and B don't match"))
     dim > 1 && return copyto!(B, A)
-    i1 = inds[1]
+    (i1, state) = iterate(inds) # We checked earlier that A isn't empty
     cur_val = v1
     B[i1] = cur_val
-    @inbounds for i in inds[2:end]
+    next = iterate(inds, state)
+    @inbounds while next !== nothing
+        (i, state) = next
         cur_val = op(cur_val, A[i])
         B[i] = cur_val
+        next = iterate(inds, state)
     end
     return B
 end

stdlib/Random/test/runtests.jl

@@ -518,7 +518,7 @@ end
     # test PRNG jump
 
     function randjumpvec(m, steps, len) # old version of randjump
-        mts = accumulate(Future.randjump, m, fill(steps, len-1))
+        mts = accumulate(Future.randjump, fill(steps, len-1); init=m)
         pushfirst!(mts, m)
         mts
     end

test/arrayops.jl

@@ -2283,6 +2283,9 @@ end
     @test accumulate(min, [1 0; 0 1], dims=1) == [1 0; 0 0]
     @test accumulate(min, [1 0; 0 1], dims=2) == [1 0; 0 0]
 
+    @test accumulate(min, [3 2 1; 3 2 1], dims=2) == [3 2 1; 3 2 1]
+    @test accumulate(min, [3 2 1; 3 2 1], dims=2, init=2) == [2 2 1; 2 2 1]
+
     @test isa(accumulate(+, Int[]), Vector{Int})
     @test isa(accumulate(+, Int[]; init=1.), Vector{Float64})
     @test accumulate(+, [1,2]; init=1) == [2, 4]
@@ -2311,6 +2314,7 @@ end
     arr = randn(4)
     oarr = OffsetArray(arr, (-3,))
     @test accumulate(+, oarr).parent == accumulate(+, arr)
+    @test accumulate(+, oarr, init = 10).parent == accumulate(+, arr; init = 10)
 
     @inferred accumulate(+, randn(3))
     @inferred accumulate(+, randn(3); init=1)