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[libcxx] Add deduction guides for shared_ptr and weak_ptr

Authored by logan-5 on Oct 29 2019, 9:58 PM.



This patch adds deduction guides to <memory> to allow deducing construction of shared_ptrs from unique_ptrs, and from weak_ptrs and vice versa, as specified by C++17.

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rCXX libc++

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logan-5 created this revision.Oct 29 2019, 9:58 PM
logan-5 updated this revision to Diff 227139.Oct 30 2019, 10:31 AM

Add a newline to synopsis

The tests should be more comprehensive; they should ASSERT_SAME_TYPE(decltype(s), XXX) to make sure that the deduction guides actually return the correct type, rather than just compile.


When you're testing type-deduction, I find it much easier to convince myself that the types are correct if you are explicit whenever possible (instead of just auto everywhere)

using SP = std::shared_ptr<A>;
using WP = std::weak_ptr<A>;

SP s0 = new A;
WP w = s0;
auto s = std::shared_ptr(w);
ASSERT_SAME_TYPE(decltype(s), SP);

Also, you should check the value of s. Make sure it points to the same thing as s0.

mclow.lists requested changes to this revision.Oct 31 2019, 11:34 PM
This revision now requires changes to proceed.Oct 31 2019, 11:34 PM
logan-5 updated this revision to Diff 227493.Nov 1 2019, 11:39 AM

Beefed up the tests in response to some feedback -- thanks.

logan-5 marked an inline comment as done.Nov 18 2019, 11:12 AM


Hello! Pinging this again.

mclow.lists accepted this revision.Sun, Dec 29, 8:44 PM

This looks good to me now.
You need to update www/cxx17_status.html appropriately as well.

This revision is now accepted and ready to land.Sun, Dec 29, 8:44 PM

Thanks Marshall. As for www/cxx1z_status.html, my best guess is that it doesn't need updating, since the row for P0433R2 lists it as In progress, which I believe is still the case after this patch. Please correct me if I'm wrong. Otherwise, I'd be grateful if someone with commit access could help me tie a bow around this.