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Section: 220.127.116.11 [util.smartptr.getdeleter] Status: NAD Submitter: Daniel Krügler Opened: 2007-09-27 Last modified: 2017-02-03
Priority: Not Prioritized
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The following issue was raised by Alf P. Steinbach in c.l.c++.mod:
According to the recent draft N2369, both the header memory synopsis of 23.10 [memory] and 18.104.22.168 [util.smartptr.getdeleter] declare:
template<class D, class T> D* get_deleter(shared_ptr<T> const& p);
This allows to retrieve the pointer to a mutable deleter of a const shared_ptr (if that owns one) and therefore contradicts the usual philosophy that associated functors are either read-only (e.g. key_comp or value_comp of std::map) or do at least reflect the mutability of the owner (as seen for the both overloads of unique_ptr::get_deleter). Even the next similar counter-part of get_deleter - the two overloads of function::target in the class template function synopsis 22.214.171.124 [func.wrap.func] or in 126.96.36.199.5 [func.wrap.func.targ] - do properly mirror the const-state of the owner.
Possible proposed resolutions:
Replace the declarations of get_deleter in the header <memory> synopsis of 23.10 [memory] and in 188.8.131.52 [util.smartptr.getdeleter] by one of the following alternatives (A) or (B):
template<class D, class T> const D* get_deleter(shared_ptr<T> const& p);
Alberto Ganesh Barbati adds:
Replace it with two functions:
template <class D, class T> D get_deleter(shared_ptr<T> const&); template <class D, class T> bool has_deleter(shared_ptr<T> const&);
The first one would throw if D is the wrong type, while the latter would never throw. This approach would reflect the current praxis of use_facet/has_facet, with the twist of returning the deleter by value as container::get_allocator() do.
Peter Dimov adds:
My favorite option is "not a defect". A, B and C break useful code.
[ Bellevue: ]
Concern this is similar to confusing "pointer to const" with "a constant pointer".