Kefu Chai c37f4e5252 treewide: use fmt::join() when appropriate ...

now that fmtlib provides fmt::join(). see
https://fmt.dev/latest/api.html#_CPPv4I0EN3fmt4joinE9join_viewIN6detail10iterator_tI5RangeEEN6detail10sentinel_tI5RangeEEERR5Range11string_view
there is not need to revent the wheel. so in this change, the homebrew
join() is replaced with fmt::join().

as fmt::join() returns an join_view(), this could improve the
performance under certain circumstances where the fully materialized
string is not needed.

please note, the goal of this change is to use fmt::join(), and this
change does not intend to improve the performance of existing
implementation based on "operator<<" unless the new implementation is
much more complicated. we will address the unnecessarily materialized
strings in a follow-up commit.

some noteworthy things related to this change:

* unlike the existing `join()`, `fmt::join()` returns a view. so we
  have to materialize the view if what we expect is a `sstring`
* `fmt::format()` does not accept a view, so we cannot pass the
  return value of `fmt::join()` to `fmt::format()`
* fmtlib does not format a typed pointer, i.e., it does not format,
  for instance, a `const std::string*`. but operator<<() always print
  a typed pointer. so if we want to format a typed pointer, we either
  need to cast the pointer to `void*` or use `fmt::ptr()`.
* fmtlib is not able to pick up the overload of
  `operator<<(std::ostream& os, const column_definition* cd)`, so we
  have to use a wrapper class of `maybe_column_definition` for printing
  a pointer to `column_definition`. since the overload is only used
  by the two overloads of
  `statement_restrictions::add_single_column_parition_key_restriction()`,
  the operator<< for `const column_definition*` is dropped.

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

2023-03-16 20:34:18 +08:00

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