Transitive const sucks

[Walter Bright]

Steven Schveighoffer wrote:
> "Walter Bright" <newshound1 at digitalmars.com> wrote in message 
>> 1) Make functional style programming possible, which will become extremely 
>> important as people will start using all those lovely cores.
> 
> How does making const transitive allow for functional programming?  From 
> what I understand (and that's not much) about functional programming, it's 
> programming without side effects.  Consider:

Although const is necessary for f.p., it is not sufficient for f.p., as 
your example illustrates.

> I think in order to allow functional programming, you need to introduce a 
> new type of const, for example fconst.  If a function is declared fconst, it 
> is not allowed to change any data that is not local to the function, or call 
> a non-fconst function, or to read non-fconst data.  If a piece of data is 
> declared fconst, it cannot be changed.

The thought is to declare a function as 'pure'.


>> 3) Be able to treat invariant references as value types. This, for 
>> example, makes manipulating strings as easy as manipulating ints.
> 
> I don't understand this, perhaps someone can explain it further.  An example 
> of how this helps would be good.

Strings in, say, Perl or Basic "just work". Just like integers "just 
work" in C. Nobody ever gives a thought to them inadvertently changing 
value.

But strings in C, everybody worries about them changing value, and such 
is a major source of bugs.

>> 4) Makes COW programming checkable and enforceable. (COW programming is an 
>> important part of many styles of programming.) Without transitive const, 
>> COW is overly reliant on programmer discipline.
> 
> All I can find on the net about COW programming is the COW programming 
> language.  I'm sure this isn't what you meant :)  can you please explain 
> this further?

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