rust 43 lines · 7 steps

A scope-guard timer with Drop in Rust

A struct that captures a start time on creation and logs the elapsed duration automatically when it goes out of scope.

Explained by highlit
Intermediate raii drop-guard timing tracing instrumentation
1use std::time::Instant;
2use tracing::info;
3 
4pub struct Timer {
5 label: &'static str,
6 start: Instant,
7}
8 
9impl Timer {
10 pub fn start(label: &'static str) -> Self {
11 Self {
12 label,
13 start: Instant::now(),
14 }
15 }
16}
17 
18impl Drop for Timer {
19 fn drop(&mut self) {
20 let elapsed = self.start.elapsed();
21 info!(
22 label = self.label,
23 elapsed_ms = elapsed.as_secs_f64() * 1000.0,
24 "completed in {:.2?}",
25 elapsed
26 );
27 }
28}
29 
30pub fn rebuild_search_index(documents: &[Document]) -> Result<IndexStats, IndexError> {
31 let _timer = Timer::start("rebuild_search_index");
32 
33 let mut writer = SearchWriter::open()?;
34 for doc in documents {
35 writer.add(doc.id, &doc.tokenized_body())?;
36 }
37 writer.commit()?;
38 
39 Ok(IndexStats {
40 documents: documents.len(),
41 segments: writer.segment_count(),
42 })
43}
01 / 01
STEP 01

Walkthrough

Space play ←→ step click any line
Three takeaways
  1. 1Implementing `Drop` turns a value's end-of-scope into a guaranteed cleanup or measurement hook.
  2. 2Binding a guard to a local like `_timer` ties its lifetime to the enclosing block without any manual teardown.
  3. 3RAII makes instrumentation robust because the timer fires even when an early `?` return aborts the function.

Related explainers

rust 
use std::collections::HashMap;
use std::sync::{Arc, Mutex};
use std::thread;
 

Aggregating metrics across threads in Rust

concurrency shared-state mutex
Intermediate 7 steps
rust 
use std::sync::{mpsc, Arc, Mutex};
use std::thread;
use std::time::Duration;
 

Building a thread pool in Rust

concurrency channels thread-pool
Advanced 9 steps
rust 
use std::collections::HashMap;
 
pub struct Memoizer<K, V, F> {
    cache: HashMap<K, V>,

A generic memoizer in Rust

memoization generics caching
Intermediate 6 steps
rust 
use std::collections::HashMap;
 
#[derive(Debug, Clone)]
struct Order {

Aggregating Rust data with fold and entry

fold hashmap ownership
Intermediate 6 steps
rust 
use axum::{extract::State, http::StatusCode, response::IntoResponse, Json};
use serde::{Deserialize, Serialize};
use uuid::Uuid;
 

Building a typed create_user handler in Axum

serde extractors sqlx
Intermediate 7 steps
rust 
use axum::{
    response::sse::{Event, KeepAlive, Sse},
    routing::get,
    Router,

Streaming live price ticks with SSE in Axum

server-sent-events broadcast-channel streaming
Advanced 8 steps

Share this explainer

Here's the card — post it anywhere.

A scope-guard timer with Drop in Rust — share card
Made with highlit — turn any snippet into a walkthrough like this in about a minute.
Explain your code