ASF GitHub Bot commented on ARROW-2408:

andygrove commented on a change in pull request #1846: ARROW-2408: [Rust] 
Ability to get `&mut [T]` from `Buffer<T>`
URL: https://github.com/apache/arrow/pull/1846#discussion_r179949092

 File path: rust/src/builder.rs
 @@ -48,6 +47,18 @@ impl<T> Builder<T> {
+    /// Get the internal byte-aligned memory buffer as a mutable slice
+    pub fn slice_mut(&self, start: usize, end: usize) -> &mut [T] {
+        unsafe {
+            slice::from_raw_parts_mut(self.data.offset(start as isize), (end - 
start) as usize)
+        }
+    }
+    /// Override the length
+    pub fn set_len(&mut self, len: usize) {
 Review comment:
   OK I have time to look at this today. I agree with @luben that for this 
method, adding assertions to make it safe is the way to go and I just pushed a 
commit for that.
   I also think @crepererum raises good points so I have filed seperate JIRA 
https://issues.apache.org/jira/browse/ARROW-2417 to review the API for safety.

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> [Rust] It should be possible to get a &mut[T] from Builder<T>
> -------------------------------------------------------------
>                 Key: ARROW-2408
>                 URL: https://issues.apache.org/jira/browse/ARROW-2408
>             Project: Apache Arrow
>          Issue Type: New Feature
>          Components: Rust
>            Reporter: Andy Grove
>            Assignee: Andy Grove
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 0.10.0
> I am currently adding Arrow support to the parquet-rs crate and I found a 
> need to get a mutable slice from a Buffer<T> to pass to the parquet column 
> reader methods.

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