szaszm commented on code in PR #1543:
URL: https://github.com/apache/nifi-minifi-cpp/pull/1543#discussion_r1158428649
##########
libminifi/include/utils/StringUtils.h:
##########
@@ -88,7 +87,15 @@ class StringUtils {
*/
static std::optional<bool> toBool(const std::string& input);
- static std::string toLower(std::string_view str);
+ static inline std::string toLower(std::string_view str) {
+ const auto tolower = [](auto c) { return std::tolower(static_cast<unsigned
char>(c)); };
+ return str | ranges::views::transform(tolower) | ranges::to<std::string>();
+ }
+
+ static inline std::string toUpper(std::string_view str) {
+ const auto toupper = [](auto c) { return std::toupper(static_cast<unsigned
char>(c)); };
+ return str | ranges::views::transform(toupper) | ranges::to<std::string>();
+ }
Review Comment:
The dumber version of taking a `std::string` by value, and doing in-place
transform would be more efficient, because it allows NRVO, and better
optimization
demonstration: https://godbolt.org/z/q5qWqGbnx
above version: 3 allocations, 1 copy
std::string version: 1 allocation (of the passed-in string)
We need 1 allocation either way, to construct the result, but by taking a
std::string by value, we push this responsibility to the caller, who may be
able to avoid it by reusing an existing std::string object. If the string is
moved in from an existing object, the resulting assembly is basically
equivalent to passing in a pointer to the string, and doing an in-place
transform, with no extra allocation, but the interface keeps the
value-semantics, and falls back to copy when necessary.
```suggestion
static inline std::string toLower(std::string str) {
const auto tolower = [](auto c) { return
std::tolower(static_cast<unsigned char>(c)); };
std::transform(std::begin(str), std::end(str), std::begin(str), tolower);
return str;
}
static inline std::string toUpper(std::string str) {
const auto toupper = [](auto c) { return
std::toupper(static_cast<unsigned char>(c)); };
std::transform(std::begin(str), std::end(str), std::begin(str), toupper);
return str;
}
```
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