Add soa crate

Cargo.lock

@@ -3178,6 +3178,7 @@ dependencies = [
  "roc_parse",
  "roc_region",
  "roc_serialize",
+ "soa",
  "static_assertions",
  "ven_pretty",
 ]
@@ -3577,6 +3578,13 @@ version = "1.11.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "942b4a808e05215192e39f4ab80813e599068285906cc91aa64f923db842bd5a"
 
+[[package]]
+name = "soa"
+version = "0.0.1"
+dependencies = [
+ "pretty_assertions",
+]
+
 [[package]]
 name = "socket2"
 version = "0.4.9"

Cargo.toml

@@ -22,6 +22,7 @@ members = [
     "crates/valgrind",
     "crates/tracing",
     "crates/utils/*",
+    "crates/soa",
     "crates/docs",
     "crates/docs_cli",
     "crates/linker",
@@ -74,6 +75,8 @@ inkwell = { git = "https://github.com/roc-lang/inkwell", branch = "inkwell-llvm-
     "llvm16-0",
 ] }
 
+soa = { path = "crates/soa" }
+
 arrayvec = "0.7.2" # update roc_std/Cargo.toml on change
 backtrace = "0.3.67"
 base64-url = "1.4.13"
@@ -137,7 +140,10 @@ maplit = "1.0.2"
 memmap2 = "0.5.10"
 mimalloc = { version = "0.1.34", default-features = false }
 nonempty = "0.8.1"
-object = { version = "0.32.2", default-features = false, features = ["read", "write"] }
+object = { version = "0.32.2", default-features = false, features = [
+    "read",
+    "write",
+] }
 packed_struct = "0.10.1"
 page_size = "0.5.0"
 palette = "0.6.1"

crates/compiler/can/src/copy.rs

@@ -12,7 +12,7 @@ use roc_module::{
 use roc_types::{
     subs::{
         self, AliasVariables, Descriptor, GetSubsSlice, OptVariable, RecordFields, Subs, SubsIndex,
-        SubsSlice, TupleElems, UnionLambdas, UnionTags, Variable, VariableSubsSlice,
+        SubsSlice, TupleElems, UnionLambdas, UnionTags, Variable, VariableSlice,
     },
     types::{RecordField, Uls},
 };
@@ -162,7 +162,7 @@ impl<'a> CopyEnv for AcrossSubs<'a> {
     fn clone_field_names(&mut self, field_names: SubsSlice<Lowercase>) -> SubsSlice<Lowercase> {
         SubsSlice::extend_new(
             &mut self.target.field_names,
-            self.source.get_subs_slice(field_names).iter().cloned(),
+            self.source.get_slice(field_names).iter().cloned(),
         )
     }
 
@@ -173,10 +173,7 @@ impl<'a> CopyEnv for AcrossSubs<'a> {
     ) -> SubsSlice<usize> {
         SubsSlice::extend_new(
             &mut self.target.tuple_elem_indices,
-            self.source
+            self.source.get_slice(tuple_elem_indices).iter().cloned(),
-                .get_subs_slice(tuple_elem_indices)
-                .iter()
-                .cloned(),
         )
     }
 
@@ -184,7 +181,7 @@ impl<'a> CopyEnv for AcrossSubs<'a> {
     fn clone_tag_names(&mut self, tag_names: SubsSlice<TagName>) -> SubsSlice<TagName> {
         SubsSlice::extend_new(
             &mut self.target.tag_names,
-            self.source.get_subs_slice(tag_names).iter().cloned(),
+            self.source.get_slice(tag_names).iter().cloned(),
         )
     }
 
@@ -192,7 +189,7 @@ impl<'a> CopyEnv for AcrossSubs<'a> {
     fn clone_lambda_names(&mut self, lambda_names: SubsSlice<Symbol>) -> SubsSlice<Symbol> {
         SubsSlice::extend_new(
             &mut self.target.symbol_names,
-            self.source.get_subs_slice(lambda_names).iter().cloned(),
+            self.source.get_slice(lambda_names).iter().cloned(),
         )
     }
 
@@ -203,7 +200,7 @@ impl<'a> CopyEnv for AcrossSubs<'a> {
     ) -> SubsSlice<RecordField<()>> {
         SubsSlice::extend_new(
             &mut self.target.record_fields,
-            self.source.get_subs_slice(record_fields).iter().copied(),
+            self.source.get_slice(record_fields).iter().copied(),
         )
     }
 }

crates/soa/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "soa"
+description = "Struct-of-Array helpers"
+
+authors.workspace = true
+edition.workspace = true
+license.workspace = true
+version.workspace = true
+
+[dependencies]
+pretty_assertions.workspace = true
+
+[dev-dependencies]

crates/soa/src/lib.rs

@@ -0,0 +1,5 @@
+mod soa_index;
+mod soa_slice;
+
+pub use soa_index::*;
+pub use soa_slice::*;

crates/soa/src/soa_index.rs

@@ -0,0 +1,50 @@
+use core::fmt;
+
+use crate::soa_slice::Slice;
+
+/// An index into an array of values, based
+/// on an offset into the array rather than a pointer.
+///
+/// Unlike a Rust pointer, this is a u32 offset
+/// rather than usize.
+pub struct Index<T> {
+    pub index: u32,
+    pub(crate) _marker: core::marker::PhantomData<T>,
+}
+
+impl<T> fmt::Debug for Index<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "Index<{}>({})", core::any::type_name::<T>(), self.index)
+    }
+}
+
+// derive of copy and clone does not play well with PhantomData
+
+impl<T> Copy for Index<T> {}
+
+impl<T> Clone for Index<T> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl<T> Index<T> {
+    pub const fn new(start: u32) -> Self {
+        Self {
+            index: start,
+            _marker: core::marker::PhantomData,
+        }
+    }
+
+    pub fn push_new(vector: &mut Vec<T>, value: T) -> Self {
+        let index = Self::new(vector.len() as _);
+
+        vector.push(value);
+
+        index
+    }
+
+    pub const fn as_slice(self) -> Slice<T> {
+        Slice::new(self.index, 1)
+    }
+}

crates/soa/src/soa_slice.rs

@@ -0,0 +1,112 @@
+use core::fmt;
+use core::iter::Map;
+
+use crate::soa_index::Index;
+
+/// A slice into an array of values, based
+/// on an offset into the array rather than a pointer.
+///
+/// Unlike a Rust slice, this is a u32 offset
+/// rather than a pointer, and the length is u16.
+pub struct Slice<T> {
+    pub start: u32,
+    pub length: u16,
+    _marker: core::marker::PhantomData<T>,
+}
+
+impl<T> fmt::Debug for Slice<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(
+            f,
+            "Slice {{ start: {}, length: {} }}",
+            self.start, self.length
+        )
+    }
+}
+
+// derive of copy and clone does not play well with PhantomData
+
+impl<T> Copy for Slice<T> {}
+
+impl<T> Clone for Slice<T> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl<T> Default for Slice<T> {
+    fn default() -> Self {
+        Self::empty()
+    }
+}
+
+impl<T> Slice<T> {
+    pub fn empty() -> Self {
+        Self {
+            start: 0,
+            length: 0,
+            _marker: Default::default(),
+        }
+    }
+
+    pub fn get_slice<'a>(&self, slice: &'a [T]) -> &'a [T] {
+        &slice[self.indices()]
+    }
+
+    pub fn get_slice_mut<'a>(&self, slice: &'a mut [T]) -> &'a mut [T] {
+        &mut slice[self.indices()]
+    }
+
+    #[inline(always)]
+    pub fn indices(&self) -> core::ops::Range<usize> {
+        self.start as usize..(self.start as usize + self.length as usize)
+    }
+
+    pub const fn len(&self) -> usize {
+        self.length as usize
+    }
+
+    pub const fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    pub const fn new(start: u32, length: u16) -> Self {
+        Self {
+            start,
+            length,
+            _marker: std::marker::PhantomData,
+        }
+    }
+
+    pub fn extend_new(vec: &mut Vec<T>, it: impl IntoIterator<Item = T>) -> Self {
+        let start = vec.len();
+
+        vec.extend(it);
+
+        let end = vec.len();
+
+        Self::new(start as u32, (end - start) as u16)
+    }
+}
+
+impl<T> IntoIterator for Slice<T> {
+    type Item = Index<T>;
+
+    #[allow(clippy::type_complexity)]
+    type IntoIter = Map<core::ops::Range<u32>, fn(u32) -> Self::Item>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        (self.start..(self.start + self.length as u32)).map(u32_to_index)
+    }
+}
+
+fn u32_to_index<T>(i: u32) -> Index<T> {
+    Index {
+        index: i,
+        _marker: core::marker::PhantomData,
+    }
+}
+
+pub trait GetSlice<T> {
+    fn get_slice(&self, slice: Slice<T>) -> &[T];
+}