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Section: 23.4.3.3 [string.cons] Status: C++14 Submitter: Bo Persson Opened: 2011-07-01 Last modified: 2016-01-28
Priority: Not Prioritized
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Discussion:
Sub-clause 23.4.3.3 [string.cons] contains these constructors in paragraphs 2 and 3:
basic_string(const basic_string<charT,traits,Allocator>& str); basic_string(basic_string<charT,traits,Allocator>&& str) noexcept;[…]
-3- Throws: The second form throws nothing if the allocator's move constructor throws nothing.
How can it ever throw anything if it is marked noexcept?
[2011-07-11: Daniel comments and suggests wording changes]
Further, according to paragraph 18 of the same sub-clause:
basic_string(const basic_string& str, const Allocator& alloc); basic_string(basic_string&& str, const Allocator& alloc);[…]
-18- Throws: The second form throws nothing if alloc == str.get_allocator() unless the copy constructor for Allocator throws.
The constraint "unless the copy constructor for Allocator throws" is redundant, because according to Table 28 — Allocator requirements, the expressions
X a1(a); X a(b);
impose the requirement: "Shall not exit via an exception".
[ 2011 Bloomington. ]
Move to Ready.
Proposed resolution:
This wording is relative to the FDIS.
Change 23.4.3.3 [string.cons] p3 as indicated (This move constructor has a wide contract and is therefore safely marked as noexcept):
basic_string(const basic_string<charT,traits,Allocator>& str); basic_string(basic_string<charT,traits,Allocator>&& str) noexcept;-2- Effects: Constructs an object of class basic_string as indicated in Table 64. In the second form, str is left in a valid state with an unspecified value.
-3- Throws: The second form throws nothing if the allocator's move constructor throws nothing.
Change 23.4.3.3 [string.cons] p18 as indicated (This move-like constructor may throw, if the allocators don't compare equal, but not because of a potentially throwing allocator copy constructor, only because the allocation attempt may fail and throw an exception):
basic_string(const basic_string& str, const Allocator& alloc); basic_string(basic_string&& str, const Allocator& alloc);[…]
-18- Throws: The second form throws nothing if alloc == str.get_allocator()unless the copy constructor for Allocator throws.