I propose to add a new set of find functions for basic_string and basic_string_view, which take and return iterators instead of indices. These functions will have the same name as the existing ones, but with an “x” prefix.

Before:

if (auto start = s.find(c); start != std::string::npos)
{
  std::transform(s.begin() + start, s.begin() + start + c.size(), s.begin() + start, [](unsigned char c) { return std::toupper(c); });
}

After:

if (auto start = s.xfind(c); start != s.end()) {
  std::transform(start, start + c.size(), start, [](unsigned char c){ return std::toupper(c); });
}

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