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From: brangdon@cix.co.uk (Dave Harris)
Newsgroups: comp.std.c++
Subject: Re: Are literals const?
Date: Wed, 22 Aug 2001 21:49:37 GMT
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pdimov@mmltd.net (Peter Dimov) wrote (abridged):
> What do you think about this piece of code:
> 
> int main()
> {
>   int const & r = 5;
>   const_cast<int &>(r) = 6;
> }
> 
> Is this legal? I think that it is.

I think it is too. The first line is, the second line is and I don't see 
any undefined behaviour. The type of 5 is (int), not (const int).


> Literals aren't const (they are about 90% const, but not 100% const.)

I think the reference is bound to a temporary, not a literal. I don't 
think r is a compile-time constant (just as well given we can assign to 
it). Eg:

    int const &r = 1;
    
    switch (j) {
    case r:         // Error - not a constant.
    }

However, I don't know when and how it stops being a literal.


> Do we _really_ need non-const literals and rvalues (of built-in
> types)?

Yes. I'd prefer to minimise the differences between built-in types and 
class types. Eg:

    class Complex {
    public:
         Complex( int i, int j=0 );
         //...
    };

    Complex const &r = 1;
    const_cast<Complex &>(r) = 2;

This is more or less reasonable for class types, so it should be permitted 
for built-in types too, for the sake of templates:

    template <typename T>
    void demo() {
        T const &r = 1;
        const_cast<T &>( r ) = 2;
    }

Unless there is a strong reason to have a difference. Is there?

  Dave Harris, Nottingham, UK | "Weave a circle round him thrice,
      brangdon@cix.co.uk      |   And close your eyes with holy dread,
                              |  For he on honey dew hath fed
 http://www.bhresearch.co.uk/ |   And drunk the milk of Paradise."

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