overload permutedims for OneElement matrices

[max-vassili3v]

overload permutedims for OneElementMatrix to return OneElement

[jishnub]

This may be more general, no?

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.90%. Comparing base (f659d9f) to head (e84270d). Report is 1 commits behind head on master.

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```diff @@ Coverage Diff @@ ## master #368 +/- ## ======================================= Coverage 99.90% 99.90% ======================================= Files 8 8 Lines 1106 1110 +4 ======================================= + Hits 1105 1109 +4 Misses 1 1 ```

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[dlfivefifty]

@max-vassili3v Can you add this for more general OneElement? At the very least OneElementVector.

[max-vassili3v]

Implemented for more general OneElements, I originally excluded the implementation for OneElementVector since permutedims(::AbstractVector) uses reshape which keeps it as a OneElement

[jishnub]

Incidentally, the vector case already works on master, although we perhaps need a specialized method anyway. Perhaps we may define the method in terms of the reshape, as in Base. This way, it'll stay consistent.

julia> o = OneElement(1, 1, 2)
2-element OneElement{Int64, 1, Tuple{Int64}, Tuple{Base.OneTo{Int64}}}:
 1
 ⋅

julia> permutedims(o)
1×2 OneElement{Int64, 2, Tuple{Int64, Int64}, Tuple{Base.OneTo{Int64}, Base.OneTo{Int64}}}:
 1  ⋅