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add usage of end() hints for try emplace #2

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56 changes: 52 additions & 4 deletions include/sg14/flat_map.h
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Original file line number Diff line number Diff line change
Expand Up @@ -725,15 +725,63 @@ class flat_map {
}
}

// TODO: use the hint, here
// TODO: use more of the hint, here
template<class... Args>
iterator try_emplace(const_iterator, const Key& k, Args&&... args) {
iterator try_emplace(const_iterator hint, const Key& k, Args&&... args) {
if (empty()) {
// hint must point end()
c_.keys.emplace_back(k);
// TODO: we must make this exception-safe if the container throws
c_.values.emplace_back(static_cast<Args&&>(args)...);
return end() - 1;
}

// at least 1 element in the map

if (hint.private_impl_getkey() == c_.keys.end()) {
// check if the current last element should be ordered before k
// if yes, insert at end, else fallback to regular try_emplace because the hint is wrong
auto prev = std::prev(hint);
if (compare_(*prev.private_impl_getkey(), k)) {
c_.keys.emplace_back(k);
// TODO: we must make this exception-safe if the container throws
c_.values.emplace_back(static_cast<Args&&>(args)...);
return end() - 1;
} else {
// hint is wrong, fallback to un-hinted implementation
return try_emplace(k, static_cast<Args&&>(args)...).first;
}
}
return try_emplace(k, static_cast<Args&&>(args)...).first;
}

// TODO: use the hint, here
// TODO: use more of the hint, here
template<class... Args>
iterator try_emplace(const_iterator, Key&& k, Args&&... args) {
iterator try_emplace(const_iterator hint, Key&& k, Args&&... args) {
if (empty()) {
// hint must point end()
c_.keys.emplace_back(static_cast<Key&&>(k));
// TODO: we must make this exception-safe if the container throws
c_.values.emplace_back(static_cast<Args&&>(args)...);
return end() - 1;
}

// at least 1 element in the map

if (hint.private_impl_getkey() == c_.keys.end()) {
// check if the current last element should be ordered before k
// if yes, insert at end, else fallback to regular try_emplace because the hint is wrong
auto prev = std::prev(hint);
if (compare_(*prev.private_impl_getkey(), k)) {
c_.keys.emplace_back(static_cast<Key&&>(k));
// TODO: we must make this exception-safe if the container throws
c_.values.emplace_back(static_cast<Args&&>(args)...);
return end() - 1;
} else {
// hint is wrong, fallback to un-hinted implementation
return try_emplace(static_cast<Key&&>(k), static_cast<Args&&>(args)...).first;
}
}
return try_emplace(static_cast<Key&&>(k), static_cast<Args&&>(args)...).first;
}

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111 changes: 111 additions & 0 deletions test/flat_map_test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -226,6 +226,117 @@ TEST(flat_map, TryEmplace)
}
}


TEST(flat_map, TryEmplaceHint)
{
sg14::flat_map<int, InstrumentedWidget> fm;
sg14::flat_map<int, InstrumentedWidget>::iterator iterator;
if (true) {
// try_emplace for a non-existent key does move-from.
InstrumentedWidget w("abc");
iterator = fm.try_emplace(fm.end(), 1, std::move(w));
assert(w.is_moved_from);
assert(iterator == fm.begin());
}
if (true) {
// try_emplace over an existing key is a no-op.
InstrumentedWidget w("def");
iterator = fm.try_emplace(fm.end(), 1, std::move(w));
assert(!w.is_moved_from);
assert(fm.size() == 1);
assert(iterator->first == 1);
assert(iterator->second.str() == "abc");
}
if (true) {
// try_emplace to non-empty with correct hint.
InstrumentedWidget w("def");
iterator = fm.try_emplace(fm.end(), 2, std::move(w));
assert(w.is_moved_from);
assert(iterator == (fm.end() - 1));
assert(fm.size() == 2);
assert(iterator->first == 2);
assert(iterator->second.str() == "def");
}
if (true) {
// try_emplace to non-empty with wrong hint.
InstrumentedWidget w("qqq");
iterator = fm.try_emplace(fm.end(), 0, std::move(w));
assert(w.is_moved_from);
assert(iterator == fm.begin());
assert(fm.size() == 3);
assert(iterator->first == 0);
assert(iterator->second.str() == "qqq");
}
if (true) {
// try_emplace to non-empty with wrong hint (not end()).
InstrumentedWidget w("qqq2");
iterator = fm.try_emplace(fm.end() - 1, -1, std::move(w));
assert(w.is_moved_from);
assert(iterator == fm.begin());
assert(fm.size() == 4);
assert(iterator->first == -1);
assert(iterator->second.str() == "qqq2");
}
}

TEST(flat_map, TryEmplaceHintConstRef)
{
sg14::flat_map<int, InstrumentedWidget> fm;
sg14::flat_map<int, InstrumentedWidget>::iterator iterator;
int key;
if (true) {
// try_emplace for a non-existent key does move-from.
InstrumentedWidget w("abc");
key = 1;
iterator = fm.try_emplace(fm.end(), key, std::move(w));
assert(w.is_moved_from);
assert(iterator == fm.begin());
}
if (true) {
// try_emplace over an existing key is a no-op.
InstrumentedWidget w("def");
iterator = fm.try_emplace(fm.end(), key, std::move(w));
assert(!w.is_moved_from);
assert(fm.size() == 1);
assert(iterator->first == 1);
assert(iterator->second.str() == "abc");
}
if (true) {
// try_emplace to non-empty with correct hint.
InstrumentedWidget w("def");
key = 2;
iterator = fm.try_emplace(fm.end(), key, std::move(w));
assert(w.is_moved_from);
assert(iterator == (fm.end() - 1));
assert(fm.size() == 2);
assert(iterator->first == 2);
assert(iterator->second.str() == "def");
}
if (true) {
// try_emplace to non-empty with wrong hint.
InstrumentedWidget w("qqq");
key = 0;
iterator = fm.try_emplace(fm.end(), key, std::move(w));
assert(w.is_moved_from);
assert(iterator == fm.begin());
assert(fm.size() == 3);
assert(iterator->first == 0);
assert(iterator->second.str() == "qqq");
}
if (true) {
// try_emplace to non-empty with wrong hint (not end()).
InstrumentedWidget w("qqq2");
key = -1;
iterator = fm.try_emplace(fm.end() - 1, key, std::move(w));
assert(w.is_moved_from);
assert(iterator == fm.begin());
assert(fm.size() == 4);
assert(iterator->first == -1);
assert(iterator->second.str() == "qqq2");
}
}


TEST(flat_map, VectorBool)
{
using FM = sg14::flat_map<bool, bool>;
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