1 files changed, 110 insertions, 0 deletions
diff --git a/src/support/istring.h b/src/support/istring.h
new file mode 100644
index 000000000..14f991c30
--- /dev/null
+++ b/src/support/istring.h
@@ -0,0 +1,110 @@
+/*
+ * Copyright 2022 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// Interned String type, 100% interned on creation. Comparisons are always just
+// a pointer comparison
+
+#ifndef wasm_support_istring_h
+#define wasm_support_istring_h
+
+#include <set>
+#include <string_view>
+#include <unordered_set>
+
+#include <assert.h>
+
+#include "threads.h"
+#include "utilities.h"
+
+namespace wasm {
+
+struct IString {
+private:
+  static std::string_view interned(std::string_view s, bool reuse = true);
+
+public:
+  const std::string_view str;
+
+  IString() = default;
+
+  // TODO: This is a wildly unsafe default inherited from the previous
+  // implementation. Change it?
+  IString(std::string_view str, bool reuse = true)
+    : str(interned(str, reuse)) {}
+
+  // But other C strings generally do need to be copied.
+  IString(const char* str) : str(interned(str, false)) {}
+  IString(const std::string& str) : str(interned(str, false)) {}
+
+  IString(const IString& other) = default;
+
+  IString& operator=(const IString& other) {
+    return *(new (this) IString(other));
+  }
+
+  bool operator==(const IString& other) const {
+    // Fast! No need to compare contents due to interning
+    return str.data() == other.str.data();
+  }
+  bool operator!=(const IString& other) const { return !(*this == other); }
+  bool operator<(const IString& other) const { return str < other.str; }
+  bool operator<=(const IString& other) const { return str <= other.str; }
+  bool operator>(const IString& other) const { return str > other.str; }
+  bool operator>=(const IString& other) const { return str >= other.str; }
+
+  char operator[](int x) const { return str[x]; }
+
+  operator bool() const { return str.data() != nullptr; }
+
+  // TODO: deprecate?
+  bool is() const { return bool(*this); }
+  bool isNull() const { return !bool(*this); }
+
+  std::string toString() const { return {str.data(), str.size()}; }
+
+  bool equals(std::string_view other) const { return str == other; }
+
+  bool startsWith(std::string_view prefix) const {
+    // TODO: Use C++20 `starts_with`.
+    return str.substr(0, prefix.size()) == prefix;
+  }
+  bool startsWith(IString str) const { return startsWith(str.str); }
+
+  // Disambiguate for string literals.
+  template<int N> bool startsWith(const char (&str)[N]) {
+    return startsWith(std::string_view(str));
+  }
+
+  size_t size() const { return str.size(); }
+};
+
+} // namespace wasm
+
+namespace std {
+
+template<> struct hash<wasm::IString> {
+  size_t operator()(const wasm::IString& str) const {
+    return std::hash<size_t>{}(uintptr_t(str.str.data()));
+  }
+};
+
+inline std::ostream& operator<<(std::ostream& os, const wasm::IString& str) {
+  return os << str.str;
+}
+
+} // namespace std
+
+#endif // wasm_support_istring_h