any news on const/invariant?

[Bill Baxter]

James Dennett wrote:
> Bruce Adams wrote:
> 
> [snip]
> 
>> I personally agree that const on value types in C++ is a stupid idea.
>> Meyers recommends it (effective C++) for the following case however:
>>
>> T operator*(T,T)
>>
>> if ((a*b)=c)) { //oops!
>>
>> instead of:
>>
>> if ((a*b)==c) {
>>
>> Personally I prefer to use lint to disallow assignment in boolean
>> expressions.
> 
> A good compiler can do that for you too (though using lint
> is a fine idea to supplement even a good compiler).
> 
> (Scott's advice here doesn't suit me; "do as the ints do" is
> 
>> There is a school that uses const value types even for builtins like int.
>> I am currently trying to convince people at work that it is pointless
>> and neither
>> being const correct not just a style thing.
> 
> It's not pointless, and it's not just a style thing.  It avoids
> defects, and it makes code clearer for those who are used to
> both styles.  Maybe instead of setting out to convince people of
> something, you could set out to discover which solution really
> works better in practice.  Using const has known advantages in
> expressiveness and defect elimination; apart from saving
> typing, what's the benefit of *not* recording the design
> decision that some value will not change during execution?
> It's a very lightweight, compile-time enforced invariant check.

I can't speak for all the cases the original poster was talking about, 
but const on value parameters is useless excess verbiage in my opinion.

float sin(const float) { ... }

Here I'm recording my design decision that my implementation of sin will 
not change its copy of the float argument passed in.

Great.  Callers just don't care.  Such uses of const clutter up the 
interface for no good reason in my opinion.  Most other uses of const on 
simple value types I'm ok with.

--bb