Merge commit '1531d6e543' as 'gitstatus'

gitstatus/src/string_view.h

@@ -0,0 +1,77 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_STRING_VIEW_H_
+#define ROMKATV_GITSTATUS_STRING_VIEW_H_
+
+#include <algorithm>
+#include <cstddef>
+#include <cstring>
+#include <ostream>
+#include <string>
+
+namespace gitstatus {
+
+// WARNING: StringView must not have embedded null characters. Violations cause UB.
+struct StringView {
+  StringView() : StringView("") {}
+
+  // Requires: !memchr(s.data(), 0, s.size()).
+  //
+  // WARNING: The existence of this requirement and the fact that this constructor is implicit
+  // means it's dangerous to have std::string instances with embedded null characters anywhere
+  // in the program. If you have an std::string `s` with embedded nulls, an innocent-looking
+  // `F(s)` might perform an implicit conversion to StringView and land you squarely in the
+  // Undefined Behavior land.
+  StringView(const std::string& s) : StringView(s.c_str(), s.size()) {}
+
+  // Requires: !memchr(ptr, 0, len).
+  StringView(const char* ptr, size_t len) : ptr(ptr), len(len) {}
+
+  // Requires: end >= begin && !memchr(begin, 0, end - begin).
+  StringView(const char* begin, const char* end) : StringView(begin, end - begin) {}
+
+  // Requires: strchr(s, 0) == s + N.
+  template <size_t N>
+  StringView(const char (&s)[N]) : StringView(s, N - 1) {
+    static_assert(N, "");
+  }
+
+  // Explicit because it's the only constructor that isn't O(1).
+  // Are you sure you don't already known the strings's length?
+  explicit StringView(const char* ptr) : StringView(ptr, ptr ? std::strlen(ptr) : 0) {}
+
+  bool StartsWith(StringView prefix) const {
+    return len >= prefix.len && !std::memcmp(ptr, prefix.ptr, prefix.len);
+  }
+
+  bool EndsWith(StringView suffix) const {
+    return len >= suffix.len && !std::memcmp(ptr + (len - suffix.len), suffix.ptr, suffix.len);
+  }
+
+  const char* ptr;
+  size_t len;
+};
+
+inline std::ostream& operator<<(std::ostream& strm, StringView s) {
+  if (s.ptr) strm.write(s.ptr, s.len);
+  return strm;
+}
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_STRING_VIEW_H_