io: add AsyncSeek trait #1924
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io: add AsyncSeek trait #1924
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OK. Fixed the formatting problems. |
Co-authored-by: Taiki Endo <te316e89@gmail.com>
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jebrosen
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Dec 11, 2019
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Motivation
We want to have a trait for seeking, since there's more than one object you might want to seek. This PR implements it for
FileandCursor, and there are clients with their own seekable objects.This is a tweaked version of #1641, with the code changed to use two functions instead of one, as requested in #1641 (comment).
Solution
The purpose behind using two functions is, essentially, to make the interface less fragile. If
start_seekreturns Pending, then that means nothing has happened yet. Otherwise, it has. This rule, that Pending means no side effects, is a common convention throughout Tokio's low-level API.The function that retrieves the result,
poll_complete, is the same way.cc #1256
Closes #776
Related: rust-lang/futures-rs#1553