Fix memory leake with Regex operator (#2024)

Author: Nayef211

torchtext/csrc/regex.cpp

@@ -6,6 +6,10 @@ Regex::Regex(const std::string& re_str) : re_str_(re_str) {
   compiled_pattern_ = new RE2(re_str_);
 }
 
+Regex::~Regex() {
+  delete compiled_pattern_;
+}
+
 std::string Regex::Sub(std::string str, const std::string& repl) const {
   RE2::GlobalReplace(&str, *compiled_pattern_, repl);
   return str;

torchtext/csrc/regex.h

@@ -13,6 +13,7 @@ struct Regex : torch::CustomClassHolder {
   std::string re_str_;
 
   TORCHTEXT_API Regex(const std::string& re_str);
+  TORCHTEXT_API ~Regex();
   TORCHTEXT_API std::string Sub(std::string str, const std::string& repl) const;
   TORCHTEXT_API bool FindAndConsume(re2::StringPiece* input, std::string* text)
       const;