Added formattable_ref

[anarthal]

format_context_base::append_value now uses formattable_ref instead of being a template

close #284

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.48%. Comparing base (80a8618) to head (4582da0).

Additional details and impacted files

[](https://app.codecov.io/gh/boostorg/mysql/pull/286?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg) ```diff @@ Coverage Diff @@ ## develop #286 +/- ## =========================================== - Coverage 98.48% 98.48% -0.01% =========================================== Files 135 136 +1 Lines 6554 6551 -3 =========================================== - Hits 6455 6452 -3 Misses 99 99 ``` | [Files](https://app.codecov.io/gh/boostorg/mysql/pull/286?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg) | Coverage Δ | | |---|---|---| | [include/boost/mysql/detail/format\_sql.hpp](https://app.codecov.io/gh/boostorg/mysql/pull/286?src=pr&el=tree&filepath=include%2Fboost%2Fmysql%2Fdetail%2Fformat_sql.hpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg#diff-aW5jbHVkZS9ib29zdC9teXNxbC9kZXRhaWwvZm9ybWF0X3NxbC5ocHA=) | `100.00% <100.00%> (ø)` | | | [include/boost/mysql/format\_sql.hpp](https://app.codecov.io/gh/boostorg/mysql/pull/286?src=pr&el=tree&filepath=include%2Fboost%2Fmysql%2Fformat_sql.hpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg#diff-aW5jbHVkZS9ib29zdC9teXNxbC9mb3JtYXRfc3FsLmhwcA==) | `100.00% <100.00%> (ø)` | | | [include/boost/mysql/impl/format\_sql.hpp](https://app.codecov.io/gh/boostorg/mysql/pull/286?src=pr&el=tree&filepath=include%2Fboost%2Fmysql%2Fimpl%2Fformat_sql.hpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg#diff-aW5jbHVkZS9ib29zdC9teXNxbC9pbXBsL2Zvcm1hdF9zcWwuaHBw) | `100.00% <100.00%> (ø)` | | | [include/boost/mysql/impl/format\_sql.ipp](https://app.codecov.io/gh/boostorg/mysql/pull/286?src=pr&el=tree&filepath=include%2Fboost%2Fmysql%2Fimpl%2Fformat_sql.ipp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg#diff-aW5jbHVkZS9ib29zdC9teXNxbC9pbXBsL2Zvcm1hdF9zcWwuaXBw) | `99.12% <100.00%> (ø)` | | ------ [Continue to review full report in Codecov by Sentry](https://app.codecov.io/gh/boostorg/mysql/pull/286?dropdown=coverage&src=pr&el=continue&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg). > **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg) > `Δ = absolute (impact)`, `ø = not affected`, `? = missing data` > Powered by [Codecov](https://app.codecov.io/gh/boostorg/mysql/pull/286?dropdown=coverage&src=pr&el=footer&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg). Last update [80a8618...4582da0](https://app.codecov.io/gh/boostorg/mysql/pull/286?dropdown=coverage&src=pr&el=lastupdated&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg).