🚀 go-pugleaf

In article <4hh34b$21r@ugress.uib.no> boukanov@kvark.fi.uib.no (Igor
Boukanov) writes:

|> J. Kanze (kanze@gabi-soft.fr) wrote:
|> > That it would be nice, but that there are two very big problems:

|> > 1. It would basically require a complete C++ interpreter in the
|> > compiler, and

|> But in almost all cases such interpreter is already present in C++ 
|> compilers! Because of cause all such const look expressions are correct 
|> C++ expressions so every C++ compiler has to generate a code that will 
|> evaluate them at run time and if forget about the crosscompilation case 
|> I think instead of putting the code to object file compiler can just execute 
|> it...

Generating code and interpreting it are two different things.  For
example, the code generator only knows about the current scope (stack
frame); the compiler typically has no mechanism for maintaining the
image of multiple stack frames (needed is it is to evaluate a
function) internall.

|> > 2. It would make the notion of constant expression somewhat
|> > implementation dependant.  Suppose my compiler implements the function
|> > sin as an inline invocation of a compiler built-in.  Can I then use sin
|> > in a constant expression?

|> Consider, for example, next:
|> const double x = 1.0 / (very small number); 
|> And of cause, the result will depend on exact representation of double... 

Agreed.  That is why the above is not a constant expression, according
to the draft standard.  Think about the case of a cross-compiler: it
would be very unintuitive if `1.0 / (very small number)' gave
different results than assigning 1.0 to a double variable, then
dividing the double variable by `(a very small number)'.  A
(cross-)compiler is not required to emulate the floating point
arithmetic of the target machine.

--
James Kanze         Tel.: (+33) 88 14 49 00        email: kanze@gabi-soft.fr
GABI Software, Sarl., 8 rue des Francs-Bourgeois, F-67000 Strasbourg, France
Conseils, itudes et rialisations en logiciel orienti objet --
                -- A la recherche d'une activiti dans une region francophone
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