Improve inferability of slicedim

base/abstractarraymath.jl

@@ -113,7 +113,7 @@ function slicedim(A::AbstractArray, d::Integer, i)
     d >= 1 || throw(ArgumentError("dimension must be ≥ 1"))
     nd = ndims(A)
     d > nd && (i == 1 || throw_boundserror(A, (ntuple(k->Colon(),nd)..., ntuple(k->1,d-1-nd)..., i)))
-    A[( n==d ? i : indices(A,n) for n in 1:nd )...]
+    A[setindex(indices(A), i, d)...]
 end
 
 function flipdim(A::AbstractVector, d::Integer)

base/bitarray.jl

@@ -1278,39 +1278,20 @@ end
 
 ## Data movement ##
 
-# TODO some of this could be optimized
-
-function slicedim(A::BitArray, d::Integer, i::Integer)
-    d_in = size(A)
-    leading = d_in[1:(d-1)]
-    d_out = tuple(leading..., d_in[(d+1):end]...)
-
-    M = prod(leading)
-    N = length(A)
-    stride = M * d_in[d]
-
-    B = BitArray(d_out)
-    index_offset = 1 + (i-1)*M
-
-    l = 1
-
-    if M == 1
-        for j = 0:stride:(N-stride)
-            B[l] = A[j + index_offset]
-            l += 1
-        end
+# preserve some special behavior
+function slicedim(A::BitVector, d::Integer, i::Integer)
+    d >= 1 || throw(ArgumentError("dimension must be ≥ 1"))
+    if d > 1
+        i == 1 || throw_boundserror(A, (:, ntuple(k->1,d-2)..., i))
+        A[:]
     else
-        for j = 0:stride:(N-stride)
-            offs = j + index_offset
-            for k = 0:(M-1)
-                B[l] = A[offs + k]
-                l += 1
-            end
-        end
+        fill!(BitArray{0}(), A[i]) # generic slicedim would return A[i] here
     end
-    return B
 end
 
+
+# TODO some of this could be optimized
+
 function flipdim(A::BitArray, d::Integer)
     nd = ndims(A)
     1 ≤ d ≤ nd || throw(ArgumentError("dimension $d is not 1 ≤ $d ≤ $nd"))

base/tuple.jl

@@ -18,6 +18,14 @@ getindex(t::Tuple, i::Real) = getfield(t, convert(Int, i))
 getindex{T}(t::Tuple, r::AbstractArray{T,1}) = tuple([t[ri] for ri in r]...)
 getindex(t::Tuple, b::AbstractArray{Bool,1}) = length(b) == length(t) ? getindex(t,find(b)) : throw(BoundsError(t, b))
 
+# returns new tuple; N.B.: becomes no-op if i is out-of-bounds
+setindex(x::Tuple, v, i::Integer) = _setindex((), x, v, i::Integer)
+function _setindex(y::Tuple, r::Tuple, v, i::Integer)
+    @_inline_meta
+    _setindex((y..., ifelse(length(y) + 1 == i, v, first(r))), tail(r), v, i)
+end
+_setindex(y::Tuple, r::Tuple{}, v, i::Integer) = y
+
 ## iterating ##
 
 start(t::Tuple) = 1

test/arrayops.jl

@@ -1608,6 +1608,7 @@ B = 1.5:5.5
         @test_throws ArgumentError slicedim(A,0,1)
         @test slicedim(A, 3, 1) == A
         @test_throws BoundsError slicedim(A, 3, 2)
+        @test @inferred(slicedim(A, 1, 2:2)) == collect(2:4:20)'
     end
 end