Why _castToPure in console.sol can convert a view method into pure method?

[passer-byzhang]

Hi folks, I have a question when I read the console.sol. There is a method which can convert a view method into a pure one. Will there be any changes to this method in the process？ Is there any solidity feature involved in this? and where can I learn about it?

    function _castToPure(
      function(bytes memory) internal view fnIn
    ) internal pure returns (function(bytes memory) pure fnOut) {
        assembly {
            fnOut := fnIn
        }
    }

[kanej]

Will there be any changes to this method in the process？

Perhaps it uses a bit more gas (I don't know if the compiler will optimize this), but otherwise there is no functionality change.

Is there any solidity feature involved in this?

No, it's assembly hackery.

and where can I learn about it?

https://twitter.com/devtooligan/status/1654945451584667648
https://gist.github.com/devtooligan/9031f859469138307d0976455b7ddffa