https://issues.dlang.org/show_bug.cgi?id=13958
Jack Stouffer <j...@jackstouffer.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |INVALID
--- Comment #3 from Jack Stouffer <j...@jackstouffer.com> ---
Using side effects in range code is a recipe for disaster. From the
std.range.isInputRange docs,
>The following are rules of input ranges are assumed to hold true in all Phobos
>code. These rules are not checkable at compile-time, so not conforming to
>these rules when writing ranges or range based code will result in undefined
>behavior.
>...
>r.front evaluated multiple times, without calling r.popFront, or otherwise
>mutating the range object or the underlying data, yields the same result for
>every evaluation.
This code breaks that assumption, as map does not cache the results of the
lambda.
However this works,
import std.stdio, std.algorithm, std.array;
static a = ["a", "b", "c", "d", "e", "f", "g", "h", "i"];
void main()
{
size_t idx = 0;
writeln(a.map!(s => s ~ a[idx + 1 == a.length ? idx :
++idx]).cache.joiner(", "));
}
Closing as invalid.
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