Subarray of an array with undefined members.

[amitmurthy]

It ought to be possible to get a sub array of an array with undefined members - for cases where you want to allocate an array once and then use different functions to populate different parts of the array.

foo = cell(10)
init1(foo[1:4])
init2(foo[5:end])

Currently

julia> foo=cell(3)
3-element Any Array:
 #undef
 #undef
 #undef

julia> bar=foo[2:end]
ERROR: access to undefined reference
 in unsafe_copy! at array.jl:51
 in copy! at array.jl:61
 in getindex at array.jl:295

I understand why the above is happening but is it possible just to leave the same fields as undefined in the subarray?

[kmsquire]

You said you understood, but just to clear things up for anyone else that might be reading, f[2:end] is a copy of the values from 2:end, and isnt' a SubArray:

julia> foo = cell(3)
3-element Any Array:
 #undef
 #undef
 #undef

julia> bar = sub(foo, 2:3)
2-element SubArray of 3-element Any Array:
 #undef
 #undef

So you're asking that undefined references be copied when you create a new array from a reference to part of that array? How is that useful?

[amitmurthy]

Sorry, I was using the term "sub array" to mean "part of the original array" and not in the Julian sense. I understand now that the part range of an array will always results in a copy.

[kmsquire]

No worries. There's actually been a lot of recent discussion on making f[2:end] an actual SubArray, but there are some sticking points.