Re: Whose idea to make it a function?

"Greg Herlihy" <>
Tue, 4 Jul 2006 02:29:46 CST
Frederick Gotham wrote:

"Bo Persson" posted:

Because floating point values are not compile time constants. (Think

Hmm... the following snippet suggests otherwise:

int main()
    char *p = 25235.25225 ? 0 : 1;

The above program shows that a floating point literal is a compile-time
constant - but that fact was not being questioned. The challenge was to
replace a floating point literal with a symbolic constant - and without
the program being at all affected by the change.

So revising the above program to:

    const double kConstDouble = 25235.25225;

    int main()
         char *p = kConstDouble ? 0 : 1; // error: invalid conversion

is a better test. And even though this program's logic appears to be
unchanged from the original, it is no longer the same program. This
revised version no compiles successfully because 1 is not a type of
pointer (whereas the original program simply eliminated the false case
of the conditional expression altogether.)

In essence there is really no difference in efficiency whether
numeric_limits<double> is declared as a constant and as an inline
function - because neither is a constant expression. And given that (in
general) methods should be favored over direct access to data (to
promote encapsulation), there is a good argument for
numeric_limit::max's current implementation.

There is also a good argument for changing the rules governing constant
expressions in C++. At least that was my conclusion after reading the
"Generalized Constant Expressions" proposal found here:


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