bkietz commented on code in PR #36915:
URL: https://github.com/apache/arrow/pull/36915#discussion_r1287323046
##########
cpp/src/arrow/type.cc:
##########
@@ -2090,17 +2090,39 @@ Status SchemaBuilder::AreCompatible(const
std::vector<std::shared_ptr<Schema>>&
return Merge(schemas, policy).status();
}
+std::vector<std::shared_ptr<Field>> make_fields(
+ std::initializer_list<std::pair<std::string, std::shared_ptr<DataType>>>
init_list) {
+ std::vector<std::shared_ptr<Field>> fields;
+ fields.reserve(init_list.size());
+ for (const auto& [name, type] : init_list) {
+ fields.push_back(field(name, type));
+ }
Review Comment:
The elements of an initializer list are always const, so calling move() on
them won't accomplish anything. We could elide the copy by making the
initializer lists accept string_view instead of string, though:
```
std::vector<std::shared_ptr<Field>> MakeFields(
std::initializer_list<std::pair<std::string_view,
std::shared_ptr<DataType>>> init_list) {
for (const auto& [name, type] : init_list) {
fields.push_back(field(std::string{name}, type));
}
}
```
However I've seldom seen a field name longer than 22 chars, so they'd be
inlined in most STL impls.
From a perf golf standpoint, the larger annoyance is the type, which must be
copied (since we don't have a nice implicitly constructible non-owning DataType
holder) and which hits atomics when copied. If you wanted to get around *that*
you'd need something like:
```
struct DataTypeView {
// NOLINTNEXTLINE
DataTypeView(const std::shared_ptr<DataType>& type) : type{type} {}
// NOLINTNEXTLINE
operator std::shared_ptr<DataType>() const { return type; }
const std::shared_ptr<DataType>& type;
};
std::vector<std::shared_ptr<Field>> MakeFields(
std::initializer_list<std::pair<std::string_view, DataTypeView>>
init_list) {
for (const auto& [name, type] : init_list) {
fields.push_back(field(std::string{name}, type));
}
}
```
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