Arrays.md

Arrays as Containers

Definitely 0.5:

• Flip the switch on the concatenation deprecation (#8599)
• Deprecate partial linear indexing (#5396, #14770)
• ReshapedArrays (#10507, #15449, https://groups.google.com/d/msg/julia-dev/7M5qzmXIChM/kOTlGSIvAwAJ)
• Julia native bounds checking and removal (#7799, #14474)
• Drop dimensions indexed by a scalar (#13612)
• Full APL slicing (#15431)

Maybe 0.5

• Disallow indexing with extra trailing singletons?

After 0.5

• Return slices as views (#9150).
• Allow any index type in non-scalar indexing (#12567)

Linear Algebra

• Transpose returns a covector or transpose type (#4774)
• Ditch special lowering of Ac_mul_Bt, use dispatch instead. (#5332)
• Remove default no-op behavior for (c)transpose (#13171)

I realize I didn't spell out the connection between ReshapedArrays and linear algebra:

• currently we dispatch to BLAS for StridedArray;
• currently reshape(sub(A, indexes...), sz) creates a copy (returning an Array, which is Strided)
• hence, this can be passed to BLAS

In a future world, reshape(sub(A, indexes...), sz) isn't Strided and so can't be passed to BLAS. Hence we rely on our fallbacks for linear algebra, which do indexing like A[i,j] and this will be slow.

The problems only crop up when you mix reshape and sub or slice. If A[:, 2:3] is going to not be a view in julia-0.5, this may not be sufficiently common to be a blocker.