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join((), ",") fails #26871

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mbauman opened this issue Apr 20, 2018 · 1 comment
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join((), ",") fails #26871

mbauman opened this issue Apr 20, 2018 · 1 comment
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bug Indicates an unexpected problem or unintended behavior iteration Involves iteration or the iteration protocol

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@mbauman
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mbauman commented Apr 20, 2018 

julia> join((), ",")
ERROR: TypeError: in fieldtype, expected DataType, got Type{Union{}}
Stacktrace:
 [1] fixpoint_iter_type at ./iterators.jl:1081 [inlined]
 [2] Type at ./iterators.jl:1055 [inlined]
 [3] join at ./strings/io.jl:239 [inlined]
 [4] #sprint#354 at ./strings/io.jl:99 [inlined]
 [5] sprint at ./strings/io.jl:95 [inlined]
 [6] join(::Tuple{}, ::String) at ./strings/io.jl:248
 [7] top-level scope

The Iterators.Stateful iterator does not handle the case where next(v, s) is guaranteed to be an error and thus inference infers it as Union{}. This is the case for next((), start(())).
@mbauman mbauman mentioned this issue Apr 20, 2018
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@mbauman mbauman added iteration Involves iteration or the iteration protocol bug Indicates an unexpected problem or unintended behavior labels Apr 20, 2018
@mbauman mbauman mentioned this issue May 10, 2018
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mbauman added a commit that referenced this issue May 10, 2018
@mbauman
Fix join((), ", ")
47d8eed 
This is a simply hack to avoid working with an `Iterators.Stateful(())`, which has problems when trying to stably infer the return type of the error function `next((), _)`. Punts #26871 to just using `Stateful` itself.
@mbauman mbauman mentioned this issue May 10, 2018
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JeffBezanson pushed a commit that referenced this issue May 14, 2018
@mbauman @JeffBezanson
Fix join((), ", ") (#27062)
ca764ea 
This is a simply hack to avoid working with an `Iterators.Stateful(())`, which has problems when trying to stably infer the return type of the error function `next((), _)`. Punts #26871 to just using `Stateful` itself.
@KristofferC
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#27062

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@mbauman @KristofferC