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⚡ Bolt: [performance improvement] avoid temporary allocations in format string generation #124

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Merged
Tcode-Motion merged 1 commit into from
Sep 10, 2026
Merged

⚡ Bolt: [performance improvement] avoid temporary allocations in format string generation #124

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3 changes: 3 additions & 0 deletions .jules/bolt.md
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Original file line number Diff line number Diff line change
Expand Up @@ -14,3 +14,6 @@
## 2024-05-24 - Avoid `push_str(&format!(...))` in loops
**Learning:** Using `push_str(&format!(...))` inside loops creates unnecessary temporary String allocations because `format!` allocates a new `String` which is then appended and immediately dropped.
**Action:** Use `std::fmt::Write` and the `write!` macro directly onto the target string buffer instead.
## 2025-02-12 - String allocation optimization
**Learning:** In heavily used loops, especially for rendering or stringifying tasks, `push_str(&format!(...))` allocates temporary strings unnecessarily. Replacing it with `write!` directly onto the mutable `String` buffer (using `std::fmt::Write`) skips the intermediate allocations and improves performance significantly.
**Action:** Use `std::fmt::Write` and the `write!` macro instead of `push_str(&format!(...))` when generating strings in loops to prevent temporary allocations and improve performance.
40 changes: 19 additions & 21 deletions stdlib/src/web.rs
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Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
use crate::{StdFunction, StdlibModule, StdlibRegistry};
use std::collections::HashMap;
use std::fmt::Write;
use std::net::{IpAddr, SocketAddr, ToSocketAddrs};
use std::rc::Rc;
use std::sync::atomic::{AtomicBool, Ordering};
Expand Down Expand Up @@ -109,7 +110,7 @@ fn render_website(html: &mut String, dsl: &techscript_runtime::value::DslBlockVa
match prop.name.as_str() {
"title" => {
if let Some(techscript_runtime::value::RuntimeValue::Str(t)) = &prop.value {
html.push_str(&format!("<title>{}</title>", t));
let _ = write!(html, "<title>{}</title>", t);
}
}
_ => {}
Expand Down Expand Up @@ -148,12 +149,12 @@ fn render_website(html: &mut String, dsl: &techscript_runtime::value::DslBlockVa
fn render_page(html: &mut String, dsl: &techscript_runtime::value::DslBlockValue) {
html.push_str("<div class=\"page\">");
if let Some(techscript_runtime::value::RuntimeValue::Str(t)) = dsl.args.first() {
html.push_str(&format!("<h1>{}</h1>", t));
let _ = write!(html, "<h1>{}</h1>", t);
}
for prop in &dsl.properties {
if prop.name == "title" {
if let Some(techscript_runtime::value::RuntimeValue::Str(t)) = &prop.value {
html.push_str(&format!("<h2>{}</h2>", t));
let _ = write!(html, "<h2>{}</h2>", t);
}
}
}
Expand All @@ -167,12 +168,12 @@ fn render_hero(html: &mut String, dsl: &techscript_runtime::value::DslBlockValue
match prop.name.as_str() {
"title" => {
if let Some(techscript_runtime::value::RuntimeValue::Str(t)) = &prop.value {
html.push_str(&format!("<h1>{}</h1>", t));
let _ = write!(html, "<h1>{}</h1>", t);
}
}
"subtitle" => {
if let Some(techscript_runtime::value::RuntimeValue::Str(t)) = &prop.value {
html.push_str(&format!("<p class=\"subtitle\">{}</p>", t));
let _ = write!(html, "<p class=\"subtitle\">{}</p>", t);
}
}
_ => {}
Expand All @@ -188,12 +189,12 @@ fn render_section(html: &mut String, dsl: &techscript_runtime::value::DslBlockVa
match prop.name.as_str() {
"title" => {
if let Some(techscript_runtime::value::RuntimeValue::Str(t)) = &prop.value {
html.push_str(&format!("<h2>{}</h2>", t));
let _ = write!(html, "<h2>{}</h2>", t);
}
}
"id" => {
if let Some(techscript_runtime::value::RuntimeValue::Str(t)) = &prop.value {
html.push_str(&format!("<!-- id: {} -->", t));
let _ = write!(html, "<!-- id: {} -->", t);
}
}
_ => {}
Expand All @@ -211,17 +212,17 @@ fn render_card(html: &mut String, dsl: &techscript_runtime::value::DslBlockValue
match prop.name.as_str() {
"title" => {
if let Some(techscript_runtime::value::RuntimeValue::Str(t)) = &prop.value {
html.push_str(&format!("<h3>{}</h3>", t));
let _ = write!(html, "<h3>{}</h3>", t);
}
}
"text" => {
if let Some(techscript_runtime::value::RuntimeValue::Str(t)) = &prop.value {
html.push_str(&format!("<p>{}</p>", t));
let _ = write!(html, "<p>{}</p>", t);
}
}
"image" => {
if let Some(techscript_runtime::value::RuntimeValue::Str(t)) = &prop.value {
html.push_str(&format!("<img src=\"{}\" alt=\"card image\">", t));
let _ = write!(html, "<img src=\"{}\" alt=\"card image\">", t);
}
}
_ => {}
Expand Down Expand Up @@ -259,7 +260,7 @@ fn dsl_to_html(val: &RuntimeValue) -> String {
.and_then(|p| p.value.as_ref())
.map(|v| v.to_string())
.unwrap_or_else(|| "Button".to_string());
html.push_str(&format!("<button>{}</button>", label));
let _ = write!(html, "<button>{}</button>", label);
}
"link" => {
let label = dsl
Expand All @@ -276,9 +277,9 @@ fn dsl_to_html(val: &RuntimeValue) -> String {
.and_then(|p| p.value.as_ref())
.map(|v| v.to_string());
if let Some(u) = url {
html.push_str(&format!("<a href=\"{}\">{}</a>", u, label));
let _ = write!(html, "<a href=\"{}\">{}</a>", u, label);
} else {
html.push_str(&format!("<a href=\"#\">{}</a>", label));
let _ = write!(html, "<a href=\"#\">{}</a>", label);
}
}
"nav" => {
Expand All @@ -291,7 +292,7 @@ fn dsl_to_html(val: &RuntimeValue) -> String {
for prop in &dsl.properties {
if prop.name == "title" {
if let Some(RuntimeValue::Str(t)) = &prop.value {
html.push_str(&format!("<h1>{}</h1>", t));
let _ = write!(html, "<h1>{}</h1>", t);
}
}
}
Expand All @@ -303,7 +304,7 @@ fn dsl_to_html(val: &RuntimeValue) -> String {
for prop in &dsl.properties {
if prop.name == "text" {
if let Some(RuntimeValue::Str(t)) = &prop.value {
html.push_str(&format!("<p>{}</p>", t));
let _ = write!(html, "<p>{}</p>", t);
}
}
}
Expand All @@ -318,7 +319,7 @@ fn dsl_to_html(val: &RuntimeValue) -> String {
.and_then(|p| p.value.as_ref())
.map(|v| v.to_string());
if let Some(p) = placeholder {
html.push_str(&format!("<input placeholder=\"{}\">", p));
let _ = write!(html, "<input placeholder=\"{}\">", p);
} else {
html.push_str("<input>");
}
Expand Down Expand Up @@ -346,13 +347,10 @@ fn dsl_to_html(val: &RuntimeValue) -> String {
.and_then(|p| p.value.as_ref())
.map(|v| v.to_string())
.unwrap_or_else(|| "Get Started".to_string());
html.push_str(&format!(
"<a class=\"start-button\" href=\"#\">{}</a>",
label
));
let _ = write!(html, "<a class=\"start-button\" href=\"#\">{}</a>", label);
}
_ => {
html.push_str(&format!("<!-- unknown DSL block: {} -->", dsl.kind));
let _ = write!(html, "<!-- unknown DSL block: {} -->", dsl.kind);
}
}
html
Expand Down
3 changes: 2 additions & 1 deletion stdlib/src/xml.rs
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Expand Up @@ -2,6 +2,7 @@ use crate::{StdFunction, StdlibModule, StdlibRegistry};
use indexmap::IndexMap;
use std::cell::RefCell;
use std::collections::HashMap;
use std::fmt::Write;
use std::rc::Rc;
use techscript_runtime::{error::RuntimeError, value::RuntimeValue};

Expand Down Expand Up @@ -44,7 +45,7 @@ impl StdlibRegistry {
if let RuntimeValue::Map { entries, .. } = &args[0] {
for (k, v) in entries.borrow().iter() {
let val_str = v.try_into_string().unwrap_or_default();
result.push_str(&format!("<{}>{}</{}>", k, val_str, k));
let _ = write!(result, "<{}>{}</{}>", k, val_str, k);
}
}
Ok(RuntimeValue::Str(result))
Expand Down
3 changes: 2 additions & 1 deletion stdlib/src/yaml.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@ use crate::{StdFunction, StdlibModule, StdlibRegistry};
use indexmap::IndexMap;
use std::cell::RefCell;
use std::collections::HashMap;
use std::fmt::Write;
use std::rc::Rc;
use techscript_runtime::{error::RuntimeError, value::RuntimeValue};

Expand Down Expand Up @@ -47,7 +48,7 @@ impl StdlibRegistry {
if let RuntimeValue::Map { entries, .. } = &args[0] {
for (k, v) in entries.borrow().iter() {
let val_str = v.try_into_string().unwrap_or_default();
result.push_str(&format!("{}: {}\n", k, val_str));
let _ = write!(result, "{}: {}\n", k, val_str);
}
}
Ok(RuntimeValue::Str(result))
Expand Down
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