On Wednesday, 18 September 2013 at 15:22:51 UTC, bearophile wrote:
Joseph Rushton Wakeling:
I haven't yet tried alloca or other manual memory management
-- I felt a bit resistant to this as I'd prefer to keep the
code simple and readable -- but I'll give that a go too just
to see how it goes.
I'd like some stack-allocated variable-length array in
D+Phobos, as in C++14. It's also a basis to build several other
stack-allocated data structures.
Yes, that'd be useful, although in the case of this code I think
that stack vs. heap probably isn't that important. If the data
is small enough for stack allocation, the calculation will be
quick anyway.
However, my impression now is that having or not having it, or
any other method (e.g. enum T0, T1, etc.) makes absolutely no
difference, and that I might as well be simple and write 0 for
integral-types, 0.0 for floating-point.
Right. And this could be right even if you want T=Rational.
Actually, on re-testing this just now, I'm returning to my
original view. I find that if you put in raw floating-point
numbers like 0.0, 1.0 etc. the resulting code can be slower in
the case where T = float. Putting to!T or using enums as you
suggest appears to make no difference.
This is a guess rather than confirmed by looking at assembly, but
I'm presuming that to!T(0) and other conversions of compile-time
constants are evaluated at compile time, so you don't in practice
carry the cost you'd normally get from using to().
