RE: [Plib-devel] PLIB developers needed.

[Dave M. <Dav...@dy...>]

Steve wrote:
>  I tried to compile PLIB on an SGI machine at work - and your 
> 'const-ification' of the clock
> routine stopped it from compiling on the IRIX compiler.
> 
> You had:
> 
>   class ulClock
>   {
>     ...
>     public:
>       ...
>       int getSomething () const { return something ; }
>       ...
>    } ;
> 
> The 'const' seemed to do *bad* things to the SGI compiler.
> 
> Could you remind me what exactly a 'const' right there 
> actually *does*? 
> 
> ...and then remove them anyway!
>
I use 'const' in only two ways:

1) const data -- const Type* foo ;
2) const method -- Type getSomething () const ;

#1 means you can't change what foo points to.  You already use this heavily
in SG.  #2 means that the class method getSomething cannot change its
instance.  it is commonly used for inline 'query' methods.  #1 and #2 are
often used together.  for example, if you write a function like this:

void checkfoo ( const Type* foo )
{
  return ( foo -> getSomething () == 42 ) ;
}

if getSomething() is not a 'const' method then you get a warning because it
thinks you are changing what foo points to.  the alternative is casting away
the 'const' of foo ala ((Type*)foo) which is not as clear.

I really thought 'Type getSomething () const' was a very portable and
standard idiom.  Could you check the SGI documentation on that?  If needed,
I will remove the 'const' methods as you advise.

--Dave