On Monday, 29 March 2021 at 01:39:16 UTC, Adam D. Ruppe wrote:
On Monday, 29 March 2021 at 01:24:13 UTC, Preetpal wrote:
writeln(isRandomAccessRange(arr));
Template arguments are passed by !(), not just ().
I believe you must also pass `typeof(arr)` since
isRandomAccessRange is only interested in types.
Thanks. This answer led me in the right direction. What I was
really trying to figure out was why I was not able to use the
std.random library to take a random sampling from an instance of
char[].
void main() {
import std.random;
import std.range;
import std.stdio;
import std.string;
char[] arr = ['a', 'b', 'c'];
int[] arr2 = [1, 2, 3];
writeln(isRandomAccessRange!(typeof(arr)));
writeln(typeid(10.iota));
writeln(typeid(arr[0..$]));
writeln(hasLength!(typeof(arr)));
writeln(hasLength!(typeof(arr2)));
auto rnd = Random(unpredictableSeed);
auto randomnumbers = 3.iota.randomSample(2, rnd);
writeln(randomnumbers);
// auto randomchars = arr.randomSample(2, rnd).array; // does
not work
auto randomchars = arr.representation.randomSample(2,
rnd).array;
writeln(cast(char[])randomchars);
}
I could not understand the error messages that the compiler was
giving me. The fact that the compiler was providing candidates
was leading me to believe that there was a type deduction issue
(like as if it was not able to choose between candidates because
of an ambiguity). This led me to not pay attention to the most
important part of the the error message related to the type
constraints.
mini_example.d(19): Error: template std.random.randomSample
cannot deduce function from argument types !()(char[], int,
MersenneTwisterEngine!(uint, 32u, 624u, 397u, 31u, 2567483615u,
11u, 4294967295u, 7u, 2636928640u, 15u, 4022730752u, 18u,
1812433253u)), candidates are:
b:\D\DMD\D\dmd2\windows\bin\..\..\src\phobos\std\random.d(3858):
randomSample(Range)(Range r, size_t n, size_t total)
b:\D\DMD\D\dmd2\windows\bin\..\..\src\phobos\std\random.d(3865):
randomSample(Range)(Range r, size_t n)
b:\D\DMD\D\dmd2\windows\bin\..\..\src\phobos\std\random.d(3872):
randomSample(Range, UniformRNG)(Range r, size_t n, size_t
total, auto ref UniformRNG rng)
b:\D\DMD\D\dmd2\windows\bin\..\..\src\phobos\std\random.d(3879):
randomSample(Range, UniformRNG)(Range r, size_t n, auto ref
UniformRNG rng)
with Range = char[],
UniformRNG = MersenneTwisterEngine!(uint, 32u, 624u, 397u,
31u, 2567483615u, 11u, 4294967295u, 7u, 2636928640u, 15u,
4022730752u, 18u, 1812433253u)
must satisfy the following constraint:
hasLength!Range
I did not realize that the compiler was telling me that the range
that I was providing did not satisfy that constraint. I only
started to try testing the type constraints as a sanity check
(which was when I ran into this error).
