Re: static const class member difficulties...style?
On 2/9/07 1:19 PM, in article
1171049352.515226.250640@h3g2000cwc.googlegroups.com, "Jeff Koftinoff"
<jeff.koftinoff@gmail.com> wrote:
On Feb 8, 12:25 pm, "Alf P. Steinbach" <a...@start.no> wrote:
<snip>...
So to be both standards-compliant and practical, it seems the way to go
is to use non-member static constants, or the template constant trick,
or for simple integral constants, enumeration type.
Cheers,
How about this:
class CThing
{
static COLORREF & theBackColor()
{
static COLORREF c = RGB(0,0,0);
return c;
}
public:
void f() { .... SetColor( theBackColor(); }
};
In this case, COLORREF could be any sort of object, even with non-
trivial constructor.
I would say that the CThing class is a very good example of how not to
implement a const COLORREF (or any other const value) for use in a C++
program.
The drawback with this kind of "Meyers singleton" approach is that it
necessitates the creation of an object to store the value. There is no way
for a program to avoid the overhead of allocating, initializing and
accessing the COLORREF object if a CThing class object is being used to
represent its value.
In reality, a class object representation for a const COLORREF value should
be completely unnecessary. There is after all little sense in allocating
storage for a value that is both unchanging and known at compile time. And
by the same reasoning, it makes even less sense for a program to incur the
runtime overhead of accessing the memory location that stores this constant
value whenever that value appears in the source code of the program.
A C++ compiler should be able to use a constant COLORREF value without the
overhead of allocating, initializing or accessing storage in memory; instead
a C++ compiler should simply be able to incorporate the constant value
directly into the compiled machine instructions whenever that constant value
appears in the source code. The other suggested solutions on this thread
support this kind of zero-overhead optimization, while the CThing approach
completely defeats it.
Greg
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