On Monday, 7 November 2016 at 22:18:56 UTC, Jerry wrote:
On Monday, 7 November 2016 at 21:37:50 UTC, Picaud Vincent
wrote:
static if ( isIntegralConstant!(typeof(required_capacity())
)
{
}
else
{
}
}
Premature post send by error sorry.... Well something like:
static if ( isIntegralConstant!(typeof(required_capacity())
)
ElementType[required_capacity()] data_;
else
ElementType[] data_;
}
For that, at least in C++, I need integral_constant<> type
with compile-time arithmetic and smooth integration with
"usual" size_t/ptrdiff_t types.
2/ I also would like to test some implementations concerning
automatic differentiation.
I have my own C++ libs, inspired, but ~20% faster than Adept:
http://www.met.reading.ac.uk/clouds/adept/
and I would like to know how I can do that in D
Well... That is the idea... I hope I will get some results and
I will be happy to share if it is something interesting.
Vincent
Ah I get what you mean, you can do that without using a special
type.
struct Vector(T, Args...) if(Args.length == 1)
{
static if(is(Args[0] == size_t))
{
size_t size;
}
else static if(Args[0] != 0) // would error if it's a
type that's not size_t
{
enum size = Args[0];
}
else
{
static assert(0);
}
}
Vector!(int, 10) a;
Vector!(int, size_t) b; // both work with IntegralConstant
could use __traits(compiles) to see if it's not a type, for
that second static if. Which would probably be better, so if
you pass a float or something, it won't give a weird error.
Thank you again Jerry!
For sure my way of thinking is twisted by my C++ habits! :-/
The positive point is that D seems to offer much shorter
solutions (this is my hope).
However I still need some investigations and/or some guidance:
-> not sure that it is ok for me as I really want to track
"static constants" all the
way long.
That is the reason why I introduced the IntegralConstant type
(with operator overloading, work in progress)
For instance, the code:
enum int a=1,b=2;
auto c = a+b;
pragma(msg,typeof(c)); // prints "int"
static assert(c==3); // compilation fails: "variable c
cannot be read at compile time"
To implement my vector structs I need:
1/ a way to detect compile-time constant vs "dynamic" values
2/ to perform and to propagate compile-time constants across
"arithmetic" computations.
For instance to compute the required capacity to store vector
data, I need something
like
auto capacity = max(0,(size_-1)*stride_);
and this expression must make sense for both "dynamic" values and
compile-time constant.
In one case I expect
typeof(capacity) -> int,
in the other
typeof(capacity) -> IntegralConst
