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Unions with 4 or more cases silently fail to utilize UseNullAsTrueValue. #510
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hi @bryanedds , this repo is for cross platoform packaing ( see http://fsharp.github.io/2014/06/18/fsharp-contributions.html for a guide) can you create or move this issue to Microsoft/visualfsharp repository?
About this issue, there is a constant UnionReprDecisions.TaggingThresholdFixedConstant = 4, below this value the UseNullAsTrueValue is applied.
This is used here
I dont know the history about of this decision, @dsyme ? we need to add a warning (error?) or remove this check?
There is already an error if the attribute cannot be applied, but the UnionReprDecisions.OptimizeAlternativeToNull is not aligned with CanHaveUseNullAsTrueValueAttribute, the only difference is this check where the constant TaggingThresholdFixedConstant is evaluated
Issue moved to - dotnet/fsharp#711
- added a commit that references this issue
on Dec 2, 2015
Repro. case in F# 4.4.0.0 -
In F# interactive, here you'll see that A is a proper value, which is not desired.
In F# interactive, here you'll see that A is a null, which is desired.
Would be a nice optimization to have this work in general. Barring that fix, a warning or error about this missing functionality might be in order.
Cheers!