[Rust] Mark methods that do not perform bounds checking as unsafe

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Reporter: Paddy Horan / @paddyhoran

_{Note: This issue was originally created as ARROW-3776. Please see the migration documentation for further details.}

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Paul Kernfeld / @paulkernfeld:
I'm interested in working on this, although there could be a lot of downstream effects. A good example of a tricky function is arrow::array::PrimitiveArray::value, which appears to be used in a couple dozen places. A few possible strategies are:

1. Add in bounds checking so that we don't need to deal with unsafe at all.

2. Propagate the unsafes up through the code.

3. Maintain a safe and unsafe version of each function that is currently unsafe.

   Personally I'm a fan of ARROW-5: Update drill-fmpp-maven-plugin to 1.5.0 #1 because I think that reducing unsafe code will help developers and users avoid mistakes (I accidentally wrote a nondeterministic unit test earlier this week). However, I'm new to the project so I'm happy to do what others think is best.

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Paddy Horan / @paddyhoran:
I was actually thinking we would need #3.  Taking value as an example I would be in favor of adding bounds checking to value and having a value_unchecked that does no bounds checking and is unsafe.

I think that we need to provide the unsafe versions for maximum performance due to Arrow often being described as a development platform rather than a front end API.  i.e. people will use it as the foundation of other higher level libraries and so developers will want the option to avoid bounds checking for performance reasons.

 

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Andrew Lamb / @alamb:
Migrated to github: https://api.github.com/repos/apache/arrow-rs/issues/28

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Andrew Lamb / @alamb:
apache/arrow-rs#28

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Andrew Lamb / @alamb:
Testing automated script to migrate issues, trying again

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Andrew Lamb / @alamb:
Migrated to github: apache/arrow-rs#29