Boost C++ Libraries: Ticket #9851: Iterators from rang have different category than the range

anonymous — Tue, 08 Apr 2014 11:18:14 GMT

Strangely, removing the line

auto c = vector<int>(b::begin(b), b::end(b));

results in the output "1, 1" instead of "0, 0", so it seems like merely chaining together adaptors causes the functions to be called. Perhaps the problem is caused by something other than iterator categories after all.

Neil Groves — Tue, 06 May 2014 11:06:22 GMT

Replying to anonymous:

Strangely, removing the line
auto c = vector<int>(b::begin(b), b::end(b));
results in the output "1, 1" instead of "0, 0", so it seems like merely chaining together adaptors causes the functions to be called. Perhaps the problem is caused by something other than iterator categories after all.

This is because range adaptors are applied lazily. Therefore the change in invocation counts is correct behaviour.

status changed

Neil Groves — Tue, 06 May 2014 11:10:12 GMT

status new → assigned

The reason you originally get 5,3 as a result is because the Filtered adaptor requires a ForwardPassRange since it needs to check adjacent elements.

http://www.boost.org/doc/libs/1_55_0/libs/range/doc/html/range/reference/adaptors/reference/filtered.html

Your code snippet is legal since it isn't a single-pass range as the input. Passing a genuine SinglePassRange to an adaptor requiring a ForwardRange will typically trigger a compile-time error with a Concept Assert. Having looked through the code I can see that I should add some more concept assert statements to ensure invalid code fails to compile.

Neil Groves — Tue, 06 May 2014 22:42:26 GMT

Concept checking has been added to all of the Boost.Range adaptors. I have added 24 compilation failure unit tests to cover adaptors that require more than a SinglePassRange.

I'll watch the unit tests on develop for a few cycles and merge to master when the release cycle allows.

milestone changed

Neil Groves — Wed, 07 May 2014 00:10:59 GMT

milestone To Be Determined → Boost 1.57.0

anonymous — Tue, 13 May 2014 11:27:04 GMT

Your code snippet is legal since it isn't a single-pass range as the input.

Isn't the input to filtered the output from transformed? The documentation for transformed says the range category is single-pass. Wouldn't that make my code snippet illegal?

Neil Groves — Wed, 28 May 2014 16:35:19 GMT

Yes it does make it illegal. This is what I was thinking, but not what I wrote in my previous comment! I meant that the code snippet was illegal. This was why I was mentioning that I ought to make the error more obvious at compile-time with Concept Assertions.

I'm sorry I messed up my comment previously. I'll merge the change in when this is allowed by the Boost release cycle.

milestone changed

anonymous — Wed, 04 Jun 2014 11:33:40 GMT

milestone Boost 1.57.0 → Boost 1.56.0

Release window for 1.56 has been extended so I can put this into 1.56.

status changed; resolution set

Neil Groves — Wed, 04 Jun 2014 17:39:35 GMT

status assigned → closed
resolution → fixed

Merged to master and ready for release 1.56.