Re: How C++ NULL pointers can violate LSP

From: Phlip (phlip_cpp_at_yahoo.com)
Date: 07/27/04 

Date: 26 Jul 2004 19:42:16 EDT

Wavemaker wrote:

> void funk(SimCity &aCity)
> {
> aCity.throwParade();
> }
>
> There is no need to test for NULL now. Where ever "aCity" is
> created, it's the job of the client to make sure it's passed as a
> reference to funk instead of a raw pointer. funk no longer needs to
> worry about it.
>
> Whether or not a NullSimCity class is needed at this point really
> depends on the needs of the client and whether they need a do
> nothing implementation of SimCity. funk doesn't have to worry about
> that.
>
> So maybe we have another reason for using references in C++ instead
> of raw pointers?

I neglected to mention the switch to references. I always move back to them
when I run out of reasons to point.

But switching to a reference won't _enforce_ a NULL-free interface.
References still might be NULL in C++ - they are just undefined if they are.

I run out of reasons to point as an emergent property of other rules - no
'new', classes should receive references to neighbors and not create them
directly, no NULL, smart pointers, RAII, etc. 

-- 
  Phlip
  http://industrialxp.org/community/bin/view/Main/TestFirstUserInterfaces

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