Created on 2009-08-24.00:00:00 last changed 162 months ago
Proposed resolution:
Change Table 97 in [unord.req] as follows (Row b.bucket(k), Column "Assertion/..."):
Table 97 — Unordered associative container requirements (in addition to container) Expression Return type Assertion/note pre-/post-condition Complexity b.bucket(k) size_type Pre: b.bucket_count() > 0 Returns the index of the bucket in which elements with keys equivalent to k would be found, if any such element existed. Post: the return value shall be in the range [0, b.bucket_count()). Constant
[ 2010-01-31 Moved to Tentatively Ready after 5 positive votes on c++std-lib. ]
[ 2010-01-25 Choice 4 put into proposed resolution section. ]
[ 2009-08-26 Daniel adds: ]
A forth choice would be to add the pre-condition "b.bucket_count() != 0" and thus imply undefined behavior if this is violated.
Howard: I like this option too, added to the list. Further on here my own favorite solution (rationale see below):
Suggested resolution:
[Rationale: I suggest to follow choice (1). The main reason is that all associative container functions which take a key argument, are basically free of pre-conditions and non-disrupting, therefore excluding choices (3) and (4). Option (2) seems a bit unexpected to me. It would be more natural, if several similar functions would exist which would also justify the existence of a symbolic constant like npos for this situation. The value 0 is both simple and consistent, it has exactly the same role as a past-the-end iterator value. A typical use-case is:
size_type pos = m.bucket(key); if (pos != m.bucket_count()) { ... } else { ... }— end Rationale]
- Change Table 97 in [unord.req] as follows (Row b.bucket(k), Column "Assertion/..."):
Table 97 — Unordered associative container requirements (in addition to container) Expression Return type Assertion/note pre-/post-condition Complexity b.bucket(k) size_type Returns the index of the bucket in which elements with keys equivalent to k would be found, if any such element existed. Post: if b.bucket_count() != 0, the return value shall be in the range [0, b.bucket_count()), otherwise 0. Constant
Table 97 "Unordered associative container requirements" in [unord.req] says:
Table 97 — Unordered associative container requirements (in addition to container) Expression Return type Assertion/note pre-/post-condition Complexity b.bucket(k) size_type Returns the index of the bucket in which elements with keys equivalent to k would be found, if any such element existed. Post: the return value shall be in the range [0, b.bucket_count()). Constant
What should b.bucket(k) return if b.bucket_count() == 0?
I believe allowing b.bucket_count() == 0 is important. It is a very reasonable post-condition of the default constructor, or of a moved-from container.
I can think of several reasonable results from b.bucket(k) when b.bucket_count() == 0:
History | |||
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Date | User | Action | Args |
2011-08-23 20:07:26 | admin | set | status: wp -> c++11 |
2010-10-21 18:28:33 | admin | set | messages: + msg1110 |
2010-10-21 18:28:33 | admin | set | messages: + msg1109 |
2010-10-21 18:28:33 | admin | set | messages: + msg1108 |
2010-10-21 18:28:33 | admin | set | messages: + msg1107 |
2009-08-24 00:00:00 | admin | create |