Proof of concept for isbits (PR 2)

[oxinabox]

This is a rebased version of #287
(and thus also would close #271 )

I am experimenting with it again.

[codecov-io]

Codecov Report

Merging #323 (1a64338) into master (906cea0) will decrease coverage by 0.04%.
The diff coverage is 98.30%.

@@            Coverage Diff             @@
##           master     #323      +/-   ##
==========================================
- Coverage   93.80%   93.75%   -0.05%     
==========================================
  Files          32       33       +1     
  Lines        1534     1586      +52     
==========================================
+ Hits         1439     1487      +48     
- Misses         95       99       +4     

Impacted Files	Coverage Δ
src/TimeZones.jl	100.00% <ø> (ø)
src/types/timezone.jl	88.00% <ø> (ø)
src/external.jl	80.00% <80.00%> (ø)
src/types/fixedtimezone.jl	100.00% <100.00%> (ø)
src/types/variabletimezone.jl	100.00% <100.00%> (ø)
src/types/zoneddatetime.jl	96.70% <100.00%> (+0.65%)	⬆️
src/compat.jl	0.00% <0.00%> (-100.00%)	⬇️
src/parse.jl	94.44% <0.00%> (-0.02%)	⬇️
... and 1 more

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[oxinabox]

When I used this, I get:

BoundsError(TimeZone[tz"Z", tz"UTC", TimeZones.FixedTimeZone("LMT", -21036), TimeZones.FixedTimeZone("CST", -21600), TimeZones.FixedTimeZone("CDT", -21600, 3600), tz"EST", TimeZones.FixedTimeZone("CWT", -21600, 3600), TimeZones.FixedTimeZone("CPT", -21600, 3600), tz"America/Chicago"],
(16,)), Any[(getindex at array.jl:809 [inlined], 1),
(getindex at external.jl:15 [inlined], 1),

Which suggests that it is not serializing properly.

I recall @JeffBezanson saying something about overloading serialize actually doesn't work, because serializing Vector{T} doesn't call serialize(T).

Which seems to be true:

Setup:

julia> using Serialization, TimeZones

julia> zdt = ZonedDateTime(Date(2011, 6, 1), tz"America/Winnipeg")
2011-06-01T00:00:00-05:00

To check if it is serializing properly we expect that the name of the timezone would occur in the serialized stream.

We can see it does for if just serializing a ZonedDateTime

julia> iob = IOBuffer(); serialize(Serializer(iob), zdt); occursin("Winnipeg", String(take!(iob)))
true

But that it does not if serializing an array of ZonedDateTimes:

julia> iob = IOBuffer(); serialize(Serializer(iob), [zdt]); occursin("Winnipeg", String(take!(iob)))
false

[oxinabox]

I think the answer is we should be overloading write not serialize both serialize_any and serialize_array_values fall back to write>

Edit: no that isn't quite write.
serializing array values calls serialize on the elements.
except of those elements are bitstypes.
And in that case it does call something that falls back to write
https://github.com/JuliaLang/julia/blob/4996445df37e526dac2772e333caf82f1ea987f0/stdlib/Serialization/src/Serialization.jl#L272