Re: Compile Time String processing
Lance Diduck wrote:
What I am not clear on, if FPN's were allows as template non-type
paramters, and by extension in compile time expressions, how would
something like this work:
template <float F> struct foo {enum{val=0}; };
template <>struct foo<3.3333333333333>{enum{val=1}; };
template <>struct foo<3+1.0/3>{enum{val=2};};
typedef foo<10.0/3> bar;
It seems to me that the value of bar::val is indeterminate.
It's not any less portable than:
if (x == 3.3333333333) ...
but that's allowed.
Indeed,
since by definition any FP arithmetic is imprecise, it would follow
that any template matching done using FP is also imprecise.
This would make it hard to port a program.
Or is this not correct and I am missing something?
I can't see a point to the specializations above. But I can see a point
to having floating point values as arguments - think of a template that
can compute a square root at compile time, for example. Don Clugston has
implemented a whole bestiary of compile time math functions using these
D programming techniques.
To make a template string hasher that works with current standard C++
technology, the original poster may consider this:
template <char _1,char _2=0,char _3=0,char _4=0,char _5=0,char
_6=0...> //up to about 10 params
struct fold{
static const size_t hval=_1^_2^_3///etc whatever ever you are
going to do
};
Cumbersome, but works fine for small strings.
Sorry, but that's awful!
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