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<@U6YPB4SJX> sorry, i am aware that traits require these lavish impls but does rust not have any  construct like an abstract base class with virtual methods?

Though traits themselves can inherit from each other

Ooh... Actually... Will impl Trait get rid of vtables?

Why yes, yes it will! <https://github.com/rust-lang/rfcs/blob/master/text/1522-conservative-impl-trait.md>

but presumably there is still a `match` statement generated in order to determine which variant you're getting out of the method

so i think the removal of the allocation/box is the big thing?

Ooh! Traits are less expensive than I thought!

they make compilation slower, and your binary larger, but they're all specialized

(and `Fn` is one of three function traits)

which is why `Fn` isn't _really_ a special case.

So passing around `Fn`s gets properly inlined as if they were any other function call?

Ok, you're winning me over to this language

Random syntactic sugar that would make me happy: |()| and || being interchangeable

<@U06A03HV1> Can I enlist your help in <https://github.com/pantsbuild/pants/pull/5148/commits/a01221f4fb8efdc45b95e5021a9c31457ea8e90b#diff-5f54ce2d41ce4be118aab4eb95da8fe1R260> ?

If I remove wait and future wrapper from `future::done(stream.map(|r| r.data).concat2().wait())` and make the line just `stream.map(|r| r.data).concat2()`m my concat2 gives me an Err of:

RpcFailure(RpcStatus { status: Unknown, details: Some("Failed to create subchannel") })

Which feels like it's a "A reference to an important piece of environment like a threadpool or something isn't being tracked across an unsafe boundary" kind of issue

<@U06A03HV1> ^^ in case our meeting was distracting :stuck_out_tongue: