Optimize fmt::Display for Value collections

Replaced inefficient `String::from`, `format!`, and `.push_str()` logic with direct formatting writes `write!(f, ...)` to the supplied formatter inside loops for `Value::List` and `Value::Map` to avoid repeated and unnecessary heap allocations. Also removed unnecessary `.clone()` calls.

Co-authored-by: ashyanSpada <22587148+ashyanSpada@users.noreply.github.com>

Author: google-labs-jules[bot]

.jules/bolt.md

@@ -9,3 +9,7 @@
 ## 2024-05-26 - Optimize decimal conversion in Value
 **Learning:** `rust_decimal::Decimal` allows efficient and direct conversion to basic types like `i64` and `f64` via `to_i64` and `to_f64` using the `rust_decimal::prelude::ToPrimitive` trait. Converting to string and then parsing `val.to_string().parse()` is an anti-pattern as it incurs heap allocation overhead, which is bad for performance. When doing integer conversions from `Decimal`, it's critical to check `val.scale() == 0` first to maintain behavioral parity with string parsing (which would reject floats).
 **Action:** Always favor direct conversion traits like `rust_decimal::prelude::ToPrimitive` methods over stringification when converting `Decimal` values to native numeric types. Keep edge cases like `scale()` properties in mind when changing conversion methods.
+
+## 2024-05-27 - Optimize Display implementations for collections
+**Learning:** `fmt::Display` implementations involving collections (like Lists or Maps) can be highly inefficient if they build intermediate `String`s via `format!()` and `push_str()` inside loops. This causes unnecessary heap allocations.
+**Action:** Always write directly to the `fmt::Formatter` inside a loop using `write!(f, ...)` to minimize heap allocations and improve formatting performance.

src/value.rs

@@ -17,25 +17,22 @@ pub enum Value {
 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)?;
                 }
-                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)?;
                 }
-                s.push_str("}");
-                write!(f, "value map: {}", s)
+                write!(f, "}}")
             }
             Self::None => write!(f, "None"),
         }