Conversion to/from Duration from std library.

[dpc]

RIght now the state of things is rather weird, where there are two different Duration types.

[marjakm]

+1

[dbrgn]

Could we switch from re-exporting the external time::Duration to using std::time::Duration directly?

[dtolnay]

@pantaloons and I just ran into this in #serde. The standard library std::time::Duration works with Serde but time::Duration (and therefore chrono::Duration) does not.

[lifthrasiir]

This is a non-trivial breaking change that is planned in 0.3. In part, std::time::Duration is never negative while time::Duration allows negative; this requires minor but significant interface changes. For now you need to use time::Duration::{from,to}_std methods to convert between them.

[Procrat]

I would like to be able to use the implementation of the Hash trait, which is defined for std::time::Duration, but which apparently is not available for chrono::Duration.

[mqudsi]

Is it possible to drop time::Duration entirely now that there is a stable std::time::Duration? Is there a roadmap for std compatibility?

[H2CO3]

@lifthrasiir What is the state of this? Chrono is already at 0.4 yet the usage of (old)time::Duration remains prevalent. It would be really good if it weren't a pain to use one of Chrono's core data types. Also the dependence on (old)time and rustc-serialize seems dubious: those libraries are deprecated and are no longer supported. As such, they should not be depended upon.

[0xpr03]

This really is a hassle now, I can't convert a NaiveTime to a Duration at all and the 0.4 broke my workaround (which was essentially to just do some meaningless calculation-function which returned the right type). Now we've a golden cage state..

[pitdicker]

Closing as a duplicate of #497.