deed:
auto mappedThenSorted = mapped.sort(); // Error
auto mappedThenSorted = mapped.array.sort(); // Works (and
used in examples)
What am I missing in the documentation?
When you try to sort mapped, the D compiler spits out a error
message that shows the complex template constraint of sort. You
are calling sort using the default unstable algorithm.
Here I show the requirements for the unstable sort:
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
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
Bye,
bearophile
