format_string_for_each_named_arg

Summary: To replace uses of `folly::defaulted` with `folly::svformat`.

Reviewed By: dmm-fb

Differential Revision: D67211009

fbshipit-source-id: 303d99eca714aac80b45220b72c8012a2816e1dd

folly/String.h

@@ -762,6 +762,37 @@ inline bool hasSpaceOrCntrlSymbols(folly::StringPiece s) {
   return detail::simdHasSpaceOrCntrlSymbols(s);
 }
 
+struct format_string_for_each_named_arg_fn {
+  template <typename C, typename CT, typename Fn>
+  constexpr void operator()(std::basic_string_view<C, CT> str, Fn fn) const
+      noexcept(noexcept(fn(str))) {
+    using view = std::basic_string_view<C, CT>;
+    while (true) {
+      auto const pos = str.find('{');
+      auto const beg = pos == view::npos ? str.size() : pos + 1;
+      if (beg == str.size()) {
+        return; // malformed
+      }
+      if (str[beg] == '{') {
+        str = str.substr(beg + 1);
+        continue; // escaped
+      }
+      auto const end = std::min(str.find('}', pos), str.find(':', pos));
+      if (end == view::npos) {
+        return; // malformed
+      }
+      auto const arg = str.substr(beg, end - beg);
+      if (!arg.empty() && (arg[0] == '_' || std::isalpha(arg[0]))) {
+        fn(arg);
+      }
+      str = str.substr(beg);
+    }
+  }
+};
+
+inline constexpr format_string_for_each_named_arg_fn
+    format_string_for_each_named_arg{};
+
 } // namespace folly
 
 #include <folly/String-inl.h>

folly/test/BUCK

@@ -1580,6 +1580,7 @@ cpp_unittest(
         "//folly:fbvector",
         "//folly:string",
         "//folly/container:array",
+        "//folly/portability:gmock",
         "//folly/portability:gtest",
     ],
     external_deps = [

folly/test/StringTest.cpp

@@ -29,6 +29,7 @@
 
 #include <folly/FBVector.h>
 #include <folly/container/Array.h>
+#include <folly/portability/GMock.h>
 #include <folly/portability/GTest.h>
 #include <folly/test/TestUtils.h>
 
@@ -1466,3 +1467,24 @@ TEST(String, hasSpaceOrCntrlSymbolsTest) {
   ASSERT_TRUE(std::iscntrl(1));
   ASSERT_TRUE(hasSpaceOrCntrlSymbols(hasCntrl));
 }
+
+TEST(String, format_string_for_each_named_arg) {
+  auto const fn = [](std::string_view str) {
+    std::vector<std::string> out;
+    folly::format_string_for_each_named_arg(str, [&](auto sub) {
+      out.push_back(std::string(sub));
+    });
+    return out;
+  };
+  EXPECT_THAT(fn(""), testing::ElementsAre());
+  EXPECT_THAT(fn("hello"), testing::ElementsAre());
+  EXPECT_THAT(fn("{{}}"), testing::ElementsAre());
+  EXPECT_THAT(fn("hello{{}}world"), testing::ElementsAre());
+  EXPECT_THAT(fn("hello{}world"), testing::ElementsAre());
+  EXPECT_THAT(fn("hello{3}world"), testing::ElementsAre());
+  EXPECT_THAT(fn("hello{34}world"), testing::ElementsAre());
+  EXPECT_THAT(fn("hello{bob}world"), testing::ElementsAre("bob"));
+  EXPECT_THAT(fn("hello{3}world{bob}go"), testing::ElementsAre("bob"));
+  EXPECT_THAT(fn("hello{bob}world{3}go"), testing::ElementsAre("bob"));
+  EXPECT_THAT(fn("hello{bob}world{sam}go"), testing::ElementsAre("bob", "sam"));
+}