The conversion from mutable_buffer to const_buffer is morally wrong

[akrzemi1]

If possible, I would not have the conversion from mutable_buffer to const_buffer. It is semantically incorrect: a buffer intended for being written to is not always a good candidate for being read from:

char foundName_[1024]; // indeterminate values: I only intend to populate it from the file contents
const char fileName_[1024] = "names.txt"; // notice a similar variable name

auto foundName = make_buffer(foundName_, sizeof(foundName_));
auto fileName = make_buffer(fileName_, sizeof(fileName_));

auto [ec, n] = co_await stream.write_some(foundName);  // Oops: I intended to pass `fileName`
// Undefined behavior: reading indeterminate byte values

[akrzemi1]

Or at least, leave the conversion but make write_some, write, and write_at_least explicitly deleted for MutableBufferSequence.

[akrzemi1]

If people do not agree with this, then a fix is needed anyway: any_stream should check concept ConstBuffetSequence because otherwise we are getting criptic template messages from the implementation guts.