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⚡ Bolt: [performance improvement] Optimize Value Display Allocations #54

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⚡ Bolt: [performance improvement] Optimize Value Display Allocations #54

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29 changes: 29 additions & 0 deletions benches/display_value.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,29 @@
use criterion::{black_box, criterion_group, criterion_main, Criterion};
use expression_engine::Value;

fn bench_display_value(c: &mut Criterion) {
let mut list = Vec::new();
for i in 0..10 {
list.push(Value::from(i));
}

let mut map = Vec::new();
for i in 0..10 {
map.push((Value::from(format!("key{}", i)), Value::from(i)));
}

let val = Value::List(vec![
Value::from("hello"),
Value::from(42),
Value::from(true),
Value::List(list),
Value::Map(map),
]);

c.bench_function("display_value", |b| {
b.iter(|| format!("{}", black_box(&val)))
});
}

criterion_group!(benches, bench_display_value);
criterion_main!(benches);
Comment on lines +28 to +29
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Copilot AI Apr 2, 2026

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This Criterion benchmark target likely won't compile/run under cargo bench unless it is registered in Cargo.toml with harness = false. Without an explicit [[bench]] entry, Cargo uses the default benchmark harness, which conflicts with criterion_main! generating its own main (typically causing a duplicate/unknown main harness error). Add a [[bench]] name = "display_value" entry with harness = false so the new benchmark works consistently.

Copilot uses AI. Check for mistakes.
24 changes: 12 additions & 12 deletions src/value.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,29 +13,29 @@ pub enum Value {
None,
}

// Optimization: Write directly to `std::fmt::Formatter` instead of creating intermediate
// strings and calling `format!()` in a loop.
// Impact: Reduces heap allocations, avoiding O(N) allocations for Lists and Maps.
#[cfg(not(tarpaulin_include))]
impl fmt::Display for Value {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
Self::String(val) => write!(f, "value string: {}", val.clone()),
Self::Number(val) => write!(f, "value number: {}", val.clone()),
Self::Bool(val) => write!(f, "value bool: {}", val.clone()),
Self::String(val) => write!(f, "value string: {}", val),
Self::Number(val) => write!(f, "value number: {}", val),
Self::Bool(val) => write!(f, "value bool: {}", val),
Self::List(values) => {
let mut s = String::from("[");
write!(f, "value list: [")?;
for value in values {
s.push_str(format!("{},", value.clone()).as_str());
write!(f, "{},", value)?;
}
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@gemini-code-assist gemini-code-assist Bot Apr 2, 2026

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medium

The current implementation adds a trailing comma for every element in the list, resulting in output like [1,2,3,]. While this preserves the previous behavior, it is generally considered better practice to omit the trailing separator for the last element to improve readability.

Suggested change
for value in values {
s.push_str(format!("{},", value.clone()).as_str());
write!(f, "{},", value)?;
}
for (i, value) in values.iter().enumerate() {
if i > 0 {
write!(f, ",")?;
}
write!(f, "{}", value)?;
}

s.push_str("]");
write!(f, "value list: {}", s)
write!(f, "]")
}
Self::Map(m) => {
let mut s = String::from("{");
write!(f, "value map: {{")?;
for (k, v) in m {
s.push_str(format!("key: {},", k.clone()).as_str());
s.push_str(format!("value: {}; ", v.clone()).as_str());
write!(f, "key: {},value: {}; ", k, v)?;
}
Comment on lines 35 to 37
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@gemini-code-assist gemini-code-assist Bot Apr 2, 2026

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medium

The current implementation adds a trailing semicolon and space for every entry in the map, resulting in output like {key: k,value: v; key: k2,value: v2; }. It is generally preferred to omit the trailing separator for the last entry to improve the clarity of the output.

                for (i, (k, v)) in m.iter().enumerate() {
                    if i > 0 {
                        write!(f, "; ")?;
                    }
                    write!(f, "key: {},value: {}", k, v)?;
                }

s.push_str("}");
write!(f, "value map: {}", s)
write!(f, "}}")
}
Self::None => write!(f, "None"),
}
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