Re: LSP

On Friday, June 19, 2015 at 12:30:04 PM UTC+8, Bardur Arantsson wrote:
>
> On 06/18/2015 11:48 PM, Shelby wrote: 
> > On Friday, June 19, 2015 at 2:37:49 AM UTC+8, Bardur Arantsson wrote: 
> > 
> >> Uh, see the formal definition with is slightly below on the same 
> >> Wikipedia page. 
> >> 
> >> And yes, it's very hard to *not* violate that rule. Hence "prefer 
> >> composition over inheritance" and such guidelines. 
> >> 
> > 
> > Seems it is easy to not violate is for covariant List[T] for as long as 
> the 
> > types in T don't use inheritance. Well I am not really making a point am 
> I. 
> > Because being covariant on its type parameter is not inheritance. 
> > 
>
> Subtyping isn't really needed much in practice[1] if you have 
> existential types. (See e.g. Haskell.) 
>
> (Of course you could argue that existential types are a limited form of 
> subtyping, I guess.) 
>
> [1] AFAICT from my own experience. YMMV, of course. 
>
 
I provided a reference which explains what you mean[1] in my Complete 
Solutions to the Expression Problem[2]. I also had a S.O. answer on 
subtying[3] that might be helpful for brainstorming.

[1] 
http://web.archive.org/web/20110605015801/http://homepages.cwi.nl/~ralf/gpce06/paper.pdf#page=8

[2] 
http://www.coolpage.com/copute/dev/docs/Copute/ref/Complete%20solutions%20to%20the%20%93Expression%20Problem.htm

[3] 
http://stackoverflow.com/questions/7266596/why-avoid-subtyping/8352969#8352969

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