Re: [boost] [review] Review of Unordered library begins today December 7

From: Ion Gaztañaga (igaztanaga_at_[hidden])
Date: 2007-12-09 16:58:47

Thorsten Ottosen wrote:
> Well, the table at
> 
> http://igaztanaga.drivehq.com/unordered/unordered/comparison.html
> 
> says that erase() does not throw for ordered containers (which is 
> correct). Anyway, this means any argument used to assume that predicate 
> evaluation is a no-throw should be the same for unordered containers.

You are right. The draft says in 23.1 (Container requirements):

10 Unless otherwise specified (see 23.2.2.3 and 23.2.5.4) all container 
types defined in this clause meet the following additional requirements:

[...]

— no erase(), pop_back() or pop_front() function throws an exception.

so the predicate for associative container should not throw, because 
erase(const key_type &k) can't throw. On the other hand, this seems 
strange. I understand making erase(iterator) no-throw, but I find 
strange making erase(const key_type &)don't think the standard wanted to 
forbid exceptions from the predicate. Clearly unordered containers are 
different:

23.1.3.1 Exception safety guarantees [unord.req.except]

1 For unordered associative containers, no clear() function throws an 
exception. No erase() function throws an exception unless that exception 
is thrown by the container’s Hash or Pred object (if any).

Why this difference? I hope someone knows the answer ;-)

Regards,

Ion