string_view: add modifiers API and related libcxx tests

[KFilipek]

This PR contains:

• string_view: add string_view capacity API libcxx tests
• string_view: implement modifiers API for string_view
• string_view: port modifiers libcxx tests

---

This change is 

[lukaszstolarczuk]

Reviewed 5 of 5 files at r1, 1 of 1 files at r2.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @KFilipek)

---

include/libpmemobj++/string_view.hpp, line 266 at r1 (raw file):

 * The behavior is undefined if n > size().
 *
 * @param[in] n of characters to remove from the start of the view

number/count of characters to...

---

include/libpmemobj++/string_view.hpp, line 291 at r2 (raw file):

/**
 * Exchanges the view with that of v.
 * 

redundant white space

---

tests/external/libcxx/string.view/string.view.modifiers/remove_prefix.pass.cpp, line 8 at r1 (raw file):

//
//===----------------------------------------------------------------------===//

licenses :P

[KFilipek]

Reviewed 1 of 5 files at r1, 4 of 4 files at r3.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @lukaszstolarczuk)

---

include/libpmemobj++/string_view.hpp, line 266 at r1 (raw file):

Previously, lukaszstolarczuk (Łukasz Stolarczuk) wrote…

number/count of characters to...

Done. Now should sound natural, I want to leave 'n' as an parameter.

---

include/libpmemobj++/string_view.hpp, line 291 at r2 (raw file):

Previously, lukaszstolarczuk (Łukasz Stolarczuk) wrote…

redundant white space

Done.

---

tests/external/libcxx/string.view/string.view.modifiers/remove_prefix.pass.cpp, line 8 at r1 (raw file):

Previously, lukaszstolarczuk (Łukasz Stolarczuk) wrote…

licenses :P

Done.

[codecov]

Codecov Report

Merging #946 into master will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #946      +/-   ##
==========================================
+ Coverage   95.93%   95.95%   +0.02%     
==========================================
  Files          48       48              
  Lines        6146     6154       +8     
==========================================
+ Hits         5896     5905       +9     
+ Misses        250      249       -1     

Flag	Coverage Δ
#tests_clang_debug_cpp17	95.79% <ø> (-0.02%)	⬇️
#tests_gcc_debug	92.42% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
include/libpmemobj++/string_view.hpp	100.00% <100.00%> (ø)
...ude/libpmemobj++/container/concurrent_hash_map.hpp	93.36% <0.00%> (-0.11%)	⬇️
include/libpmemobj++/condition_variable.hpp	78.57% <0.00%> (+4.76%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 55351ae...5f02ba8. Read the comment docs.

[igchor]

Reviewed 1 of 5 files at r1, 4 of 4 files at r4.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @lukaszstolarczuk)

---

include/libpmemobj++/string_view.hpp, line 299 at r4 (raw file):

	basic_string_view<CharT, Traits> &v) noexcept
{
	const value_type *p = data_;

why not just:

std::swap(data_, v.data_);
std::swap(size_, v.size_);

?

[KFilipek]

Reviewed 5 of 5 files at r6.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @lukaszstolarczuk)

---

include/libpmemobj++/string_view.hpp, line 299 at r4 (raw file):

Previously, igchor (Igor Chorążewicz) wrote…

why not just:

std::swap(data_, v.data_);
std::swap(size_, v.size_);

?

Hmm, I've copied libcxx function body, but std::swap is also marked as constexpr

[lukaszstolarczuk]

Reviewed 1 of 4 files at r4, 1 of 5 files at r6.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @KFilipek)

---

include/libpmemobj++/string_view.hpp, line 266 at r1 (raw file):

Previously, KFilipek (Krzysztof Filipek) wrote…

Done. Now should sound natural, I want to leave 'n' as an parameter.

it seems good, but it does not point that it is a number/count of chars to remove (one may interpret it as a charset to remove 😉 )

[KFilipek]

Reviewable status: 4 of 5 files reviewed, 1 unresolved discussion (waiting on @KFilipek and @lukaszstolarczuk)

---

include/libpmemobj++/string_view.hpp, line 266 at r1 (raw file):

Previously, lukaszstolarczuk (Łukasz Stolarczuk) wrote…

it seems good, but it does not point that it is a number/count of chars to remove (one may interpret it as a charset to remove 😉 )

Done. I've changed it according to pmem::obj::string documentation

[lukaszstolarczuk]

Reviewed 3 of 5 files at r6, 1 of 1 files at r7.
Reviewable status: complete! all files reviewed, all discussions resolved

[igchor]

Reviewed 1 of 1 files at r7.
Reviewable status: complete! all files reviewed, all discussions resolved

[igchor]

Reviewed 2 of 2 files at r8.
Reviewable status: complete! all files reviewed, all discussions resolved

[lukaszstolarczuk]

Reviewed 2 of 2 files at r8.
Reviewable status: complete! all files reviewed, all discussions resolved