I think this is a reasonable proposal and I find the argument convincing that string.contains function appears in every other language and third-party C++ string classes.  I encourage you to submit this to LEWGI.

On Tue, May 28, 2019 at 4:31 AM Wim Leflere via Std-Proposals <std-proposals@lists.isocpp.org> wrote:
Hello,

After seeing that 'starts_with' and 'ends_with' were added to std::string in C++20 (P0457), I was wondering why 'contains' was still missing as a std::string member function.
So I wrote a proposal (starting from P0457) to add it.

Please find the draft of the proposal here:
https://github.com/WimLeflere/cpp-papers/blob/master/string_contains_function.md

I am looking forward to your valuable comments.

Thanks,

Wim Leflere 
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