bkietz commented on code in PR #36496:
URL: https://github.com/apache/arrow/pull/36496#discussion_r1307693610
##########
cpp/src/arrow/extension/fixed_shape_tensor.cc:
##########
@@ -104,6 +104,38 @@ bool FixedShapeTensorType::ExtensionEquals(const
ExtensionType& other) const {
permutation_equivalent;
}
+std::string FixedShapeTensorType::ToString() const {
+ std::stringstream ss;
+ ss << "extension<" << this->extension_name()
+ << "[value_type=" << value_type_->ToString() << ", shape=[";
+ std::string separator;
+ for (auto v : shape_) {
+ ss << separator << v;
+ separator = ",";
+ }
+ ss << "]";
+ if (!permutation_.empty()) {
+ ss << ", permutation=[";
+ std::string p_separator;
+ for (auto v : permutation_) {
+ ss << p_separator << v;
+ p_separator = ",";
+ }
+ ss << "]";
+ }
+ if (!dim_names_.empty()) {
+ ss << ", dim_names=[";
+ std::string d_separator;
+ for (std::string v : dim_names_) {
+ ss << d_separator << v;
+ d_separator = ",";
+ }
+ ss << "]";
+ }
+ ss << "]>";
+ return ss.str();
+}
+
Review Comment:
The better API idea is to vendor `fmt` to access [c++20's improved string
utils](https://fmt.dev/latest/api.html#_CPPv4I0EN3fmt4joinE9join_viewIN6detail10iterator_tI5RangeEEN6detail10sentinel_tI5RangeEEERR5Range11string_view)
```
std::vector<int> v = {1, 2, 3};
fmt::print("{}", fmt::join(v, ", "));
// Output: "1, 2, 3"
```
In lieu of that, we could add a similar template which relies on lazy
stringification through `std::ostream`:
```
template <typename Range, typename Separator>
struct JoinStrings {
const Range& range_;
const Separator& separator_;
template <typename Os> // template to dodge inclusion of <ostream>
friend Os& operator<<(Os& os, JoinStrings l) {
bool first = true;
for (const auto& element : l.range_) {
if (first) {
first = false;
} else {
os << l.separator_;
}
os << ToChars(element); // use ToChars to avoid locale dependence
}
return os;
}
};
void use() {
std::vector<int> v{1,2,3};
std::stringstream ss;
ss << JoinStrings{v, ", "};
}
```
... note that this template can only be used with an ostream, but it seems
that's mostly where the resulting output would end up anyway
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