scsmithr commented on issue #7709:
URL: https://github.com/apache/arrow-rs/issues/7709#issuecomment-2992989419
This is a perfect use case for a union.
```rust
#[derive(Clone, Copy)]
#[repr(C)]
pub union BinaryView {
inline: BinaryViewInline,
reference: BinaryViewReference,
}
#[derive(Debug, Clone, Copy)]
#[repr(C)]
pub struct BinaryViewInline {
len: i32,
inline: [u8; 12],
}
#[derive(Debug, Clone, Copy)]
#[repr(C)]
pub struct BinaryViewReference {
len: i32,
prefix: [u8; 4],
buffer_idx: i32,
offset: i32,
}
impl BinaryView {
pub fn new_inline(data: &[u8]) -> Self {
let len = data.len();
assert!(len <= 12);
let mut inline = BinaryViewInline {
len: len as i32,
inline: [0; 12],
};
inline.inline[0..len].copy_from_slice(data);
BinaryView { inline }
}
pub fn new_reference(data: &[u8], buffer_idx: i32, offset: i32) -> Self {
let len = data.len();
assert!(len > 12);
let mut reference = BinaryViewReference {
len: len as i32,
prefix: [0; 4],
buffer_idx,
offset,
};
reference.prefix.copy_from_slice(&data[0..4]);
BinaryView { reference }
}
pub const fn is_inline(&self) -> bool {
// SAFETYE: i32 len is first field in both, safe to access from
either
// variant.
unsafe { self.inline.len <= 12 }
}
pub const fn is_reference(&self) -> bool {
unsafe { self.inline.len > 12 }
}
pub const fn data_len(&self) -> i32 {
// SAFETY: `len` field is in the same place in both variants.
unsafe { self.inline.len }
}
pub const fn as_inline(&self) -> &BinaryViewInline {
assert!(self.is_inline());
unsafe { &self.inline }
}
pub const fn as_reference(&self) -> &BinaryViewReference {
assert!(!self.is_inline());
unsafe { &self.reference }
}
}
```
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