%% title = "don't use RefCell<T>"

% id = "01HCD90XT3X82R37WTJJABZF4Y"
+ usually if you have to resort to [`RefCell<T>`](https://doc.rust-lang.org/std/cell/struct.RefCell.html), it means something is wrong with your architecture

    % id = "01HCD90XT3QQA9MCB77Q04W148"
    - `Cell<T>` less so but still you should avoid it whenever possible

    % id = "01HCD90XT36Q0WTZNRCEWZQE1X"
    - `Rc<RefCell<T>>` is an immediate red flag when I read someone's code. it means they don't
    really know what they're doing and are just trying to sidestep the language

% id = "01HCD90XT3QNZ7H77Z4QMW66QJ"
- it's really not that hard to avoid, try bumping your resources up a scope and borrow them
from there

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+ using `RefCell` has a few disadvantages

    % id = "01HCD90XT3R214HQM03TSRZV6K"
    + first, `RefCell` is _literally_ turning off the borrow checker

        % id = "01HCD90XT3V4K4RKRQXX5BCCRB"
        - or really deferring it until runtime, but then what's the point. Rust's borrowing
        rules are meant to prevent bugs, not cause more of them

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    + second, your program can now panic in unexpected places, because it turns out runtime
    borrows can be really hard to predict

        % id = "01HCD90XT34QD8MCN0BA35AV0F"
        - as evidenced by a random crash I once got while using [druid](https://lib.rs/crates/druid)
        which was caused by a overlapping mutable then immutable borrows at runtime

            % id = "01HCD90XT39NZ0BSY630MFNG1X"
            - therefore maybe uhhh... don't use it in libraries? :pleading:

    % id = "01HCD90XT3GT9G16EQDAK76WEC"
    + third, it incurs a runtime overhead for the borrow checking, which in 99% of cases is
    totally unnecessary

        % id = "01HCD90XT3V3B1TVPX7GS8SPDQ"
        - (this is more about non-pessimization rather than premature microoptimization, so
        don't yell at me with your "it'll be fast enough" arguments please)

    % id = "01HCD90XT37138S38DN0V3DKHF"
    + fourth, and this one is extremely easy to spot - your code becomes really verbose!

        % id = "01HCD90XT3WNGWD4GA2Y63D42H"
        - yes please, `.borrow()` me everywhere!

        % id = "01HCD90XT361QQB2YNFBY51N2A"
        - and you end up with lots of temporaries because of the [`Ref<'b, T>`](https://doc.rust-lang.org/std/cell/struct.Ref.html)
        guards you have to keep in scope.

            % id = "01HCD90XT34K9BREXAKA5FFP3M"
            - remember that you cannot do `&ref_cell.borrow().some_field` because that would
            drop the temporary `Ref<'b, T>` guard after the expression ends