taggedalgebraic 0.11.0 adds TaggedUnion

Sönke Ludwig sludwig+d at outerproduct.org
Sat Feb 23 20:46:03 UTC 2019


Am 23.02.2019 um 20:19 schrieb Paul Backus:
> On Friday, 22 February 2019 at 17:09:41 UTC, Sönke Ludwig wrote:
>>  - Behaves like a POD if only POD fields exist, is non-copyable if any
>>    contained type is non-copyable etc.
> 
> In fact, if a contained type is non-copyable, it fails to compile 
> altogether. (Example code below.)
> 
> Granted, so do Algebraic and SumType, so this isn't a knock against 
> taggedalgebraic in particular. But it does indicate poor test coverage 
> that you listed this feature without realizing it didn't work.
> 
> --- example.d
> /+ dub.sdl:
> dependency "taggedalgebraic" version="~>0.11.2"
> +/
> import taggedalgebraic;
> 
> struct NoCopy { @disable this(this); }
> union U { NoCopy member; }
> alias Test = TaggedUnion!U; // kaboom
> 
> void main() {}
> 

You are right, I was actually aware of some places where the value is 
not moved/swapped properly, but I forgot about it when rushing the post 
before leaving. The test coverage is actually pretty good, though, even 
if it is hard to give a meaningful number for template-heavy code like that.


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