import std.algorithm, std.array, std.range;
void main() {
int[] data = [2, 0, 1];
auto mapped = data.map!q{a * 10};
alias R = typeof(mapped);
pragma(msg, hasSwappableElements!R);
pragma(msg, hasAssignableElements!R);
pragma(msg, isRandomAccessRange!R);
pragma(msg, hasSlicing!R);
pragma(msg, hasLength!R);
// auto r1 = mapped.sort(); // Error
// auto r2 = mapped.array.sort(); // OK
}
It prints:
false
false
true
true
true
Meaning sortable ranges are actually a narrow subset of random
access ranges? Why aren't the constraints listed in the docs? Are
the source files and error messages the only way to get this info?
Elements generated by a map can't be back-assigned.
To help D programmers understand such situations I have asked
for this:
http://d.puremagic.com/issues/show_bug.cgi?id=9626
Could be helpful.
Example of error message where source has to be investigated:
...\phobos\std\algorithm.d(7946): Error: r[j] is not an lvalue
from this file compiled with dmd 2.061:
import std.algorithm, std.array, std.range;
void main() {
long[] slice = [2, -1, -3];
auto mappedSortedSumOfFirstTwo =
slice.map!("a ^^ 2").
sort. // causes the error message
take(2).
reduce!("a + b");
}
