On Tue, 10 Jul 2018, Trevor Saunders wrote: > On Tue, Jul 10, 2018 at 10:43:20AM +0200, Richard Biener wrote: > > > > The following makes the hash-map iterator dereference return a pair<Key, > > Value&> rather than a copy of Value. This matches the hash-table iterator > > behavior and avoids issues with > > > > hash_map<tree, auto_vec<..., 2> > > > Eventually somebodies probably going to want > hash_map<unique_ptr<x>>, auto_vec<tree>> too, so we might as well go ahead > and make it pair<key &, value &>? > > > where iterating over the hash-table will call the auto_vec destructor > > when dereferencing the iterator. I note that the copy ctor of > > auto_vec should probably be deleted and the hash-table/map iterators > > should possibly support an alternate "reference" type to the stored > > Values so we can use vec<> for "references" and auto_vec<> for > > stored members. > > I think code somewhere uses the auto_vec copy ctor to return a auto_vec, > this is pretty similar to the situation with unique_ptr in c++98 mode. > > > But that's out of scope - the patch below seems to survive minimal > > testing at least. > > > > I suppose we still want to somehow hide the copy ctors of auto_vec? > > I suspec the best we can do is delete it in c++11 mode and provide a > auto_vec<T>(auto_vec<T> &&) move ctor instead. Though I think for the > case where auto_vec has inline storage we should be able to just delete > the copy ctor? > > > How does hash-map growth work here? (I suppose it doesn't...?) > > Yeah was going to ask, I think hash_table memcpy's the elements? in > which case memcpying a pointer into yourself isn't going to work.
It doesn't work. It uses assignment but auto_vec doesn't implement that so auto-storage breaks. So you say it should use std::move<> where that's obviously not available for us :/ > However I think if you use the auto_vec specialization for 0 internal > elements that should be able to work if we null out the old auto_vec or > avoid running dtors on the old elements. Well, then I don't really need auto_vec, I'm more interested in the embedded storage than the destructor ;) > > Any further comments? > > other than using a reference for the key type seems good. OK, I suppose it should be 'const Key&' then (hopefully that works for Key == const X / X * as intended). I guess given the expansion problem I'm going to re-think using auto_vec for now :/ Can we please move to C++11? ;) Richard.
