Merge 0.4 branch to master #115
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This seems like a trivial test, but since it can fail, it shows us that we don't have a sound implementation yet.
Use a build script to detect if we can use MaybeUninit or NoDrop. Enabling unstable features automatically is not ideal, but since it's a soundness issue we should do it. Use a MaybeUninit-like union on nightly when we can. We use a feature detection script in build.rs, so that we also go back to the fallback if the unstable feature changes in an unexpected way. We need to continue to use NoDrop for best working stable implementation, but we eagerly use our union solution where we can, currently only in nightlies. Rustc feature probe code written by Josh Stone (cuviper), taken from num-bigint.
We can't fix this properly (MaybeUninit with a union) until we change the user visible API (we need to require that A: Copy. As a temporary solution for arrayvec version 0.4.*, we use zeroed to initialize an array of bytes, instead of using uninitialized. This may have a negative performance impact, but the fix is to upgrade to future arrayvec 0.5.
Implement a "MaybeUninit" and use it conditionally (0.4.x version)
* '0.4' of https://github.com/bluss/arrayvec: 0.4.9 TEST: Add test that ensures the MaybeUninit impl is used on nightly FIX: Remove use of uninitialized in ArrayString FEAT: Implement a "MaybeUninit" and use it conditionally TEST: Add test that Some(ArrayVec<[&_;_]>).is_some() MAINT: Test the 0.4 branch in travis
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This brings the changes from #114 to the master branch which is tracking the next release which will be 0.5 (Arrayvec 1.0 does not yet reach all the checkboxes on its tracking issue #48).