Add a `string_view` overload to `absl::StrJoin`
This allows users to pass a collection of string-like objects in an
`initializer_list` without having to convert everything to the same
type first.
`initializer_list` has the requirement that everything is copied in to
the list. For strings hitting the `string_view` overload avoids
unnecessary copies.
This may be a breaking change if `absl::StrJoin` has an explicit
template parameter, for example `absl::StrJoin<std::string>({foo,
"bar"});`. In this case, remove the explicit template parameter.
PiperOrigin-RevId: 633295575
Change-Id: Ie5f0860f409f639a27a58949842ec961e0b3bdeb
diff --git a/absl/strings/str_join.h b/absl/strings/str_join.h
index 6a92c0f..badc944 100644
--- a/absl/strings/str_join.h
+++ b/absl/strings/str_join.h
@@ -247,12 +247,20 @@
return strings_internal::JoinRange(range, separator, fmt);
}
-template <typename T, typename Formatter>
+template <typename T, typename Formatter,
+ typename = typename std::enable_if<
+ !std::is_convertible<T, absl::string_view>::value>::type>
std::string StrJoin(std::initializer_list<T> il, absl::string_view separator,
Formatter&& fmt) {
return strings_internal::JoinRange(il, separator, fmt);
}
+template <typename Formatter>
+inline std::string StrJoin(std::initializer_list<absl::string_view> il,
+ absl::string_view separator, Formatter&& fmt) {
+ return strings_internal::JoinRange(il, separator, fmt);
+}
+
template <typename... T, typename Formatter>
std::string StrJoin(const std::tuple<T...>& value, absl::string_view separator,
Formatter&& fmt) {
@@ -269,9 +277,14 @@
return strings_internal::JoinRange(range, separator);
}
-template <typename T>
-std::string StrJoin(std::initializer_list<T> il,
- absl::string_view separator) {
+template <typename T, typename = typename std::enable_if<!std::is_convertible<
+ T, absl::string_view>::value>::type>
+std::string StrJoin(std::initializer_list<T> il, absl::string_view separator) {
+ return strings_internal::JoinRange(il, separator);
+}
+
+inline std::string StrJoin(std::initializer_list<absl::string_view> il,
+ absl::string_view separator) {
return strings_internal::JoinRange(il, separator);
}
diff --git a/absl/strings/str_join_test.cc b/absl/strings/str_join_test.cc
index 449f95b..cd52e11 100644
--- a/absl/strings/str_join_test.cc
+++ b/absl/strings/str_join_test.cc
@@ -428,6 +428,42 @@
}
}
+TEST(StrJoin, StringViewInitializerList) {
+ {
+ // Tests initializer_list of string_views
+ std::string b = "b";
+ EXPECT_EQ("a-b-c", absl::StrJoin({"a", b, "c"}, "-"));
+ }
+ {
+ // Tests initializer_list of string_views with a non-default formatter
+ TestingParenFormatter f;
+ std::string b = "b";
+ EXPECT_EQ("(a)-(b)-(c)", absl::StrJoin({"a", b, "c"}, "-", f));
+ }
+
+ class NoCopy {
+ public:
+ explicit NoCopy(absl::string_view view) : view_(view) {}
+ NoCopy(const NoCopy&) = delete;
+ operator absl::string_view() { return view_; } // NOLINT
+ private:
+ absl::string_view view_;
+ };
+ {
+ // Tests initializer_list of string_views preferred over initializer_list<T>
+ // for T that is implicitly convertible to string_view
+ EXPECT_EQ("a-b-c",
+ absl::StrJoin({NoCopy("a"), NoCopy("b"), NoCopy("c")}, "-"));
+ }
+ {
+ // Tests initializer_list of string_views preferred over initializer_list<T>
+ // for T that is implicitly convertible to string_view
+ TestingParenFormatter f;
+ EXPECT_EQ("(a)-(b)-(c)",
+ absl::StrJoin({NoCopy("a"), NoCopy("b"), NoCopy("c")}, "-", f));
+ }
+}
+
TEST(StrJoin, Tuple) {
EXPECT_EQ("", absl::StrJoin(std::make_tuple(), "-"));
EXPECT_EQ("hello", absl::StrJoin(std::make_tuple("hello"), "-"));
