Re: [PHP] How do I handle covariant parameters and not fall foul of LSP.

On Tue, Feb 14, 2017 at 2:20 AM, Richard Quadling <[email protected]>
 wrote:

> If the process method is doing storage related things I don't think is a
> good idea to move it to the Entity hierarchy.
>

I totally agree. I was just showing a way to avoid violating LSP.

On Tue, Feb 14, 2017 at 2:20 AM, Richard Quadling <[email protected]>
wrote:

> I still can't see why an extended BaseEntity is still not a BaseEntity,
> just a more specialised variant.
>

Because you're changing the contract in PersonEntity::processEntity() from
taking any BaseEntity to accepting only PersonEntity, you cannot substitute
any BaseEntity for it.

If anyone has some good examples (real world ideally) where LSP is sane AND
> includes inheritance (they seem to be where the conflict lies) then I may
> be able to learn why I'm doing it wrong.
>

A typical example is multiple cache backend implementations: CacheFile and
CacheMemcache. Swapping between the two requires no changes other than the
initial setup. The user of the cache shouldn't know or care which it has.

Cheers!
David