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Add more doc comments to UnionLayout enum

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Brian Carroll 2021-12-07 20:12:57 +00:00
parent 20131933e0
commit 2f4225eec6
1 changed files with 7 additions and 3 deletions
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10
compiler/mono/src/layout.rs
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@ -207,20 +207,24 @@ pub enum UnionLayout<'a> {
/// A non-recursive tag union
/// e.g. `Result a e : [ Ok a, Err e ]`
NonRecursive(&'a [&'a [Layout<'a>]]),
/// A recursive tag union
/// A recursive tag union (general case)
/// e.g. `Expr : [ Sym Str, Add Expr Expr ]`
Recursive(&'a [&'a [Layout<'a>]]),
/// A recursive tag union with just one constructor
/// Optimization: No need to store a tag ID (the payload is "unwrapped")
/// e.g. `RoseTree a : [ Tree a (List (RoseTree a)) ]`
NonNullableUnwrapped(&'a [Layout<'a>]),
/// A recursive tag union where the non-nullable variant(s) store the tag id
/// A recursive tag union that has an empty variant
/// Optimization: Represent the empty variant as null pointer => no memory usage & fast comparison
/// It has more than one other variant, so they need tag IDs (payloads are "wrapped")
/// e.g. `FingerTree a : [ Empty, Single a, More (Some a) (FingerTree (Tuple a)) (Some a) ]`
/// see also: https://youtu.be/ip92VMpf_-A?t=164
NullableWrapped {
nullable_id: u16,
other_tags: &'a [&'a [Layout<'a>]],
},
/// A recursive tag union where the non-nullable variant does NOT store the tag id
/// A recursive tag union with only two variants, where one is empty.
/// Optimizations: Use null for the empty variant AND don't store a tag ID for the other variant.
/// e.g. `ConsList a : [ Nil, Cons a (ConsList a) ]`
NullableUnwrapped {
nullable_id: bool,