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Use slice destructuring #96

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5 changes: 5 additions & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,11 @@ All notable changes to this project will be documented in this file.

Thanks to [Utkarsh Gupta](https://github.com/utkarshgupta137) for the [PR](https://github.com/danielparks/matchgen/pull/95)!

* Changed generated slice matchers to use slice destructuring bindings instead
of repeated `&slice[N..]` indexing.

This eliminates extraneous indexing checks.

## Release 0.4.0 (2025-10-31)

* Changed `TreeMatcher` to use a flat slice match, e.g. `match slice { [1, 2, 3,
Expand Down
53 changes: 30 additions & 23 deletions src/flat.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -237,7 +237,7 @@ impl FlatMatcher {
/// r#"fn match_bytes(slice: &[u8]) -> (Option<u64>, &[u8]) {
/// #[allow(unreachable_patterns)]
/// match slice {
/// [b'a', ..] => (Some(1), &slice[1..]),
/// [b'a', rest @ ..] => (Some(1), rest),
/// _ => (None, slice),
/// }
/// }
Expand Down Expand Up @@ -272,7 +272,7 @@ impl FlatMatcher {
/// fn match_bytes(slice: &[u8]) -> (Option<u64>, &[u8]) {
/// #[allow(unreachable_patterns)]
/// match slice {
/// [b'a', ..] => (Some(1), &slice[1..]),
/// [b'a', rest @ ..] => (Some(1), rest),
/// _ => (None, slice),
/// }
/// }
Expand Down Expand Up @@ -315,7 +315,7 @@ impl FlatMatcher {
/// fn match_bytes(slice: &[u8]) -> (Option<u64>, &[u8]) {
/// #[allow(unreachable_patterns)]
/// match slice {
/// [b'a', ..] => (Some(1), &slice[1..]),
/// [b'a', rest @ ..] => (Some(1), rest),
/// _ => (None, slice),
/// }
/// }
Expand Down Expand Up @@ -355,7 +355,7 @@ impl FlatMatcher {
/// fn match_bytes(slice: &[u8]) -> (Option<u64>, &[u8]) {
/// #[allow(unreachable_patterns)]
/// match slice {
/// [b'a', ..] => (Some(1), &slice[1..]),
/// [b'a', rest @ ..] => (Some(1), rest),
/// _ => (None, slice),
/// }
/// }
Expand Down Expand Up @@ -493,7 +493,7 @@ impl FlatMatcher {
/// fn match_bytes(slice: &[u8]) -> (Option<u64>, &[u8]) {
/// #[allow(unreachable_patterns)]
/// match slice {
/// [b'a', ..] => (Some(1), &slice[1..]),
/// [b'a', rest @ ..] => (Some(1), rest),
/// _ => (None, slice),
/// }
/// }
Expand Down Expand Up @@ -551,24 +551,31 @@ impl FlatMatcher {
entries.sort_by_key(|(key, _)| cmp::Reverse(key.len()));
for (key, value) in entries {
let count = key.len();
writeln!(
writer,
"{indent} [{prefix}..] => (Some({value}), {remainder}),",
indent = indent,
prefix = if count == 0 {
String::new()
} else {
key.iter()
.map(|&b| crate::fmt_byte(b) + ", ")
.collect::<String>()
},
value = value,
remainder = if self.return_slice {
format!("&slice[{}..]", count)
} else {
count.to_string()
},
)?;
let prefix = if count == 0 {
String::new()
} else {
key.iter()
.map(|&b| crate::fmt_byte(b) + ", ")
.collect::<String>()
};
if self.return_slice {
writeln!(
writer,
"{indent} [{prefix}rest @ ..] => (Some({value}), rest),",
indent = indent,
prefix = prefix,
value = value,
)?;
} else {
writeln!(
writer,
"{indent} [{prefix}..] => (Some({value}), {count}),",
indent = indent,
prefix = prefix,
value = value,
count = count,
)?;
}
}

write!(
Expand Down
55 changes: 30 additions & 25 deletions src/tree.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -152,7 +152,7 @@ impl TreeMatcher {
/// #[must_use]
/// fn match_bytes(slice: &[u8]) -> (Option<u64>, &[u8]) {
/// match slice {
/// [b'a', b'b', b'c', ..] => (Some(1), &slice[3..]),
/// [b'a', b'b', b'c', rest_3 @ ..] => (Some(1), rest_3),
/// _ => (None, slice),
/// }
/// }
Expand Down Expand Up @@ -181,9 +181,9 @@ impl TreeMatcher {
/// #[must_use]
/// fn match_bytes(slice: &[u8]) -> (Option<u64>, &[u8]) {
/// match slice {
/// [b'a', ..] => match &slice[1..] {
/// [b'b', ..] => match &slice[2..] {
/// [b'c', ..] => (Some(1), &slice[3..]),
/// [b'a', rest_1 @ ..] => match rest_1 {
/// [b'b', rest_2 @ ..] => match rest_2 {
/// [b'c', rest_3 @ ..] => (Some(1), rest_3),
/// _ => (None, slice),
/// }
/// _ => (None, slice),
Expand Down Expand Up @@ -239,7 +239,7 @@ impl TreeMatcher {
/// )]
/// fn match_bytes(slice: &[u8]) -> (Option<u64>, &[u8]) {
/// match slice {
/// [b'a', ..] => (Some(1), &slice[1..]),
/// [b'a', rest_1 @ ..] => (Some(1), rest_1),
/// _ => (None, slice),
/// }
/// }
Expand Down Expand Up @@ -289,7 +289,7 @@ impl TreeMatcher {
/// #[must_use]
/// fn match_bytes(slice: &[u8]) -> (Option<u64>, &[u8]) {
/// match slice {
/// [b'a', ..] => (Some(1), &slice[1..]),
/// [b'a', rest_1 @ ..] => (Some(1), rest_1),
/// _ => (None, slice),
/// }
/// }
Expand Down Expand Up @@ -336,7 +336,7 @@ impl TreeMatcher {
/// #[must_use]
/// fn match_bytes(slice: &[u8]) -> (Option<u64>, &[u8]) {
/// match slice {
/// [b'a', ..] => (Some(1), &slice[1..]),
/// [b'a', rest_1 @ ..] => (Some(1), rest_1),
/// _ => (None, slice),
/// }
/// }
Expand Down Expand Up @@ -380,7 +380,7 @@ impl TreeMatcher {
/// #[must_use]
/// fn match_bytes(slice: &[u8]) -> (Option<u64>, &[u8]) {
/// match slice {
/// [b'a', ..] => (Some(1), &slice[1..]),
/// [b'a', rest_1 @ ..] => (Some(1), rest_1),
/// _ => (None, slice),
/// }
/// }
Expand Down Expand Up @@ -518,7 +518,7 @@ impl TreeMatcher {
/// #[must_use]
/// fn match_bytes(slice: &[u8]) -> (Option<u64>, &[u8]) {
/// match slice {
/// [b'a', ..] => (Some(1), &slice[1..]),
/// [b'a', rest_1 @ ..] => (Some(1), rest_1),
/// _ => (None, slice),
/// }
/// }
Expand Down Expand Up @@ -656,7 +656,7 @@ where
/// #[must_use]
/// fn match_bytes(slice: &[u8]) -> (Option<u64>, &[u8]) {
/// match slice {
/// [b'a', ..] => (Some(1), &slice[1..]),
/// [b'a', rest_1 @ ..] => (Some(1), rest_1),
/// _ => (None, slice),
/// }
/// }
Expand Down Expand Up @@ -1003,7 +1003,7 @@ impl TreeNode {
/// "\
/// fn match_bytes(slice: &[u8]) -> (Option<u64>, &[u8]) {
/// match slice {
/// [b'a', ..] => (Some(1), &slice[1..]),
/// [b'a', rest_1 @ ..] => (Some(1), rest_1),
/// _ => (None, slice),
/// }
/// }
Expand Down Expand Up @@ -1054,12 +1054,15 @@ impl TreeNode {
fallback: Option<(&String, usize)>,
collapse_nested_single_arms: bool,
) -> io::Result<()> {
/// Render a subslice operation.
/// Render the binding name for the remainder slice at byte index
/// `i`. Index 0 is the function parameter `slice`; deeper levels
/// are bound by `rest_N @ ..` patterns introduced in this
/// function.
#[must_use]
#[inline]
fn slice_str(i: usize) -> String {
fn rest_name(i: usize) -> String {
if i > 0 {
format!("&slice[{}..]", i)
format!("rest_{}", i)
} else {
"slice".to_owned()
}
Expand All @@ -1073,27 +1076,27 @@ impl TreeNode {
if let Some(leaf) = &node.leaf {
writeln!(
writer,
"(Some({leaf}), {slice}){comma}",
"(Some({leaf}), {rest}){comma}",
leaf = leaf,
slice = slice_str(index),
rest = rest_name(index),
comma = comma
)
} else if let Some((value, fallback)) = fallback {
writeln!(
writer,
"(Some({value}), {slice}){comma}",
"(Some({value}), {rest}){comma}",
value = value,
slice = slice_str(fallback),
rest = rest_name(fallback),
comma = comma
)
} else {
writeln!(writer, "(None, slice){comma}", comma = comma)
}
} else {
// `&slice[n..]` returns `[]` when `n == slice.len()`, so as
// long as we return on `[]` in the previous `match`, this will
// never panic.
writeln!(writer, "match {} {{", slice_str(index))?;
// The `rest_N @ ..` binding in the enclosing arm always
// succeeds (it matches any tail, including `[]`), so this
// `match` is safe even when the remainder is empty.
writeln!(writer, "match {} {{", rest_name(index))?;

let fallback =
node.leaf.as_ref().map(|leaf| (leaf, index)).or(fallback);
Expand All @@ -1110,27 +1113,29 @@ impl TreeNode {
bytes.push(*tuple.0);
child = tuple.1;
}
let new_index = index.checked_add(bytes.len()).unwrap();
write!(
writer,
"{indent} [{bytes}..] => ",
"{indent} [{bytes}{rest} @ ..] => ",
indent = indent,
bytes = bytes
.iter()
.map(|&b| crate::fmt_byte(b) + ", ")
.collect::<String>(),
rest = rest_name(new_index),
)?;
render_child(
child,
writer,
index.checked_add(bytes.len()).unwrap(),
new_index,
&indent,
fallback,
collapse_nested_single_arms,
)?;
}

let default = if let Some((value, index)) = fallback {
format!("(Some({}), {})", value, slice_str(index))
format!("(Some({}), {})", value, rest_name(index))
} else {
"(None, slice)".to_owned()
};
Expand Down