On Sunday, 18 May 2014 at 04:19:05 UTC, David Held wrote:
How do I get an array from randomSample()?
int[] source = [ ... ];
int[] sample = randomSample(source, 3);
src\main.d(30): Error: cannot implicitly convert expression
(randomSample(source, 3u)) of type RandomSample!(int[], void)
to int[]
I get that RandomSample is a struct which implements the
necessary interface to work with foreach. But the fact that
this struct is considered a proprietary implementation detail
of std.random is a constant source of frustration for me.
Quite a few D libraries use this trick, but the opacity of
these data structures make it impossible for users to know
exactly how to use them outside of the one or two examples
given in the documentation. I don't know how to improve the
situation, other than documenting them explicitly rather than
treating them as a magical black box.
In the mean time, can anyone suggest a solution to the above,
short of actually iterating over it? I suppose someone will
say to use map!().
Dave
You need to use the function array from std.array.
import std.array;
int[] source = [ ... ];
int[] sample = randomSample(source, 3).array();
Array has the ability to turn any range into an array, and it's
generally how you convert from these structs (which generally
implement a range interface) returned by most range-based
functions in D. It can be a bit confusing at first, but returning
a range struct is much more flexible than returning a simple
array of values.
