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authorPedro Alves <palves@redhat.com>2017-04-18 21:39:24 +0100
committerPedro Alves <palves@redhat.com>2017-04-18 23:48:41 +0100
commit22796e972f18c5601cecb0251222411a352836b6 (patch)
tree0e2cdd295c54b35894588485dda6d821648540d7 /bfd/i386lynx.c
parenta7fc9b6193f830293066479aa439cea924418393 (diff)
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More gdb::optional features
Currently we can't use gdb::optional<T> as function return type, because gdb::optional's copy ctor is deleted. For example, with: gdb::optional<int> function () { gdb::optional<int> opt; .... return opt; we get: src/gdb/foo.c: In function ‘gdb::optional<int> foo()’: src/gdb/foo.c:75:10: error: use of deleted function ‘gdb::optional<T>::optional(const gdb::optional<T>&) [with T = int]’ return opt; ^ In file included from src/gdb/foo.c:68:0: src/gdb/common/gdb_optional.h:53:3: note: declared here optional (const optional &other) = delete; ^ I started by fixing that, and then ran into another missing feature, also fixed by this patch. The next feature I'm missing most from gdb::optional<T> compared to std::optional<T> is construction/move/assignment from a T, instead of having to default construct an gdb::optional and then use optional::emplace(....). For example: gdb::optional<std::string> function () { gdb::optional<std::string> opt; std::string str; ... opt.emplace (std::move (str)); return opt; vs gdb::optional<std::string> function () { std::string str; ... return str; The copy/move ctor/assign methods weren't initialy implemented because std::optional supports construction from a type U if U is convertible to T too, and has rules to decide whether the ctors are explicit/implicit based on that, and rules for whether the ctor should be trivial or not, etc., which leads to a much more complicated implementation. If we stick to supporting copy/move construction/assignment of/to an optional<T> from exactly only optional<T> and T, then all that conversion-related complication disappears, and we still gain convenience in most use cases. The patch also makes emplace return a reference to the constructor object, per C++17 std::optional, and adds a reset method, againt because std::optional has one and it's trivial to support it. These two changes are a requirement of the gdb::optional unit testing patch that will follow. gdb/ChangeLog: 2017-04-18 Pedro Alves <palves@redhat.com> * common/gdb_optional.h: Include common/traits.h. (in_place_t): New type. (in_place): New constexpr variable. (optional::optional): Remove member initialization of m_instantiated. (optional::optional(in_place_t...)): New constructor. (optional::~optional): Use reset. (optional::optional(const optional&)): New. (optional::optional(const optional&&)): New. (optional::optional(T &)): New. (optional::optional(T &&)): New. (operator::operator=(const optional &)): New. (operator::operator=(optional &&)): New. (operator::operator= (const T &)) (operator::operator= (T &&)) (operator::emplace (Args &&... args)): Return a T&. Use reset. (operator::reset): New. (operator::m_instantiated):: Add in-class initializer. * common/traits.h: Include <type_traits>. (struct And): New types.
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