commit 7c2e104ffbe4383a9d2933428d4bc104ff16cdb2
author Paul Wankadia <junyer@google.com> Thu Oct 08 07:45:41 2020 -0700
committer Paul Wankadia <junyer@google.com> Thu Oct 08 14:47:11 2020 +0000
tree 01bc9c3e9c7cdfe511eab90a92f31b1f6cefdbdc
parent fb85161dc63eb843eab31bff61828000765663d1

Refactor the RE2::Arg templates for readability.

Change-Id: I2335ae97fc19c558e39b31c8d546cceb5c2e73b6
Reviewed-on: https://code-review.googlesource.com/c/re2/+/57930
Reviewed-by: Paul Wankadia <junyer@google.com>

re2/re2.h

diff --git a/re2/re2.h b/re2/re2.h
index 9ad160a..02fc88f 100644
--- a/re2/re2.h
+++ b/re2/re2.h
@@ -816,38 +816,34 @@
 }  // namespace re2_internal
 
 class RE2::Arg {
+ private:
+  template <typename T>
+  using CanParse3ary = typename std::enable_if<
+      re2_internal::Parse3ary<T>::value,
+      int>::type;
+
+  template <typename T>
+  using CanParse4ary = typename std::enable_if<
+      re2_internal::Parse4ary<T>::value,
+      int>::type;
+
+  template <typename T>
+  using CanParseFrom = typename std::enable_if<
+      std::is_member_function_pointer<decltype(&T::ParseFrom)>::value,
+      int>::type;
+
  public:
   Arg() : Arg(nullptr) {}
-  Arg(std::nullptr_t ptr)
-      : arg_(ptr), parser_([](const char* /*str*/, size_t /*n*/, void* /*dest*/) -> bool {
-          return true;
-        }) {}
+  Arg(std::nullptr_t ptr) : arg_(ptr), parser_(DoNothing) {}
 
-  template <typename T,
-            typename std::enable_if<re2_internal::Parse3ary<T>::value,
-                                    int>::type = 0>
-  Arg(T* ptr)
-      : arg_(ptr), parser_([](const char* str, size_t n, void* dest) -> bool {
-          return re2_internal::Parse(str, n, reinterpret_cast<T*>(dest));
-        }) {}
+  template <typename T, CanParse3ary<T> = 0>
+  Arg(T* ptr) : arg_(ptr), parser_(DoParse3ary<T>) {}
 
-  template <typename T,
-            typename std::enable_if<re2_internal::Parse4ary<T>::value,
-                                    int>::type = 0>
-  Arg(T* ptr)
-      : arg_(ptr), parser_([](const char* str, size_t n, void* dest) -> bool {
-          return re2_internal::Parse(str, n, reinterpret_cast<T*>(dest), 10);
-        }) {}
+  template <typename T, CanParse4ary<T> = 0>
+  Arg(T* ptr) : arg_(ptr), parser_(DoParse4ary<T>) {}
 
-  template <typename T,
-            typename std::enable_if<!(re2_internal::Parse3ary<T>::value ||
-                                      re2_internal::Parse4ary<T>::value),
-                                    int>::type = 0>
-  Arg(T* ptr)
-      : arg_(ptr), parser_([](const char* str, size_t n, void* dest) -> bool {
-          if (dest == NULL) return true;
-          return reinterpret_cast<T*>(dest)->ParseFrom(str, n);
-        }) {}
+  template <typename T, CanParseFrom<T> = 0>
+  Arg(T* ptr) : arg_(ptr), parser_(DoParseFrom<T>) {}
 
   typedef bool (*Parser)(const char* str, size_t n, void* dest);
 
@@ -859,6 +855,26 @@
   }
 
  private:
+  static bool DoNothing(const char* /*str*/, size_t /*n*/, void* /*dest*/) {
+    return true;
+  }
+
+  template <typename T>
+  static bool DoParse3ary(const char* str, size_t n, void* dest) {
+    return re2_internal::Parse(str, n, reinterpret_cast<T*>(dest));
+  }
+
+  template <typename T>
+  static bool DoParse4ary(const char* str, size_t n, void* dest) {
+    return re2_internal::Parse(str, n, reinterpret_cast<T*>(dest), 10);
+  }
+
+  template <typename T>
+  static bool DoParseFrom(const char* str, size_t n, void* dest) {
+    if (dest == NULL) return true;
+    return reinterpret_cast<T*>(dest)->ParseFrom(str, n);
+  }
+
   void*         arg_;
   Parser        parser_;
 };