Don't place a defer inside a loop that iterates many times (especially if the loop is performance-critical). Defer calls won't run until the function returns and each call has a small overhead; instead, perform the operation directly in the loop when possible.
In a tight loop, deferring an operation on each iteration can lead to increased memory usage (each defer is stacked until function exit) and CPU overhead. This can slow down performance and delay resource release. It's more efficient to handle repetitive operations inline for large loops.
Side-by-side examples engineers can pattern-match during review.
for _, file := range files {
f, _ := os.Open(file)
defer f.Close() // defers 1000x if len(files)=1000; files stay open until after loop
processFile(f)
}for _, file := range files {
f, _ := os.Open(file)
processFile(f)
f.Close() // close immediately after processing each file
}for _, file := range files {
f, _ := os.Open(file)
defer f.Close() // defers 1000x if len(files)=1000; files stay open until after loop
processFile(f)
}for _, file := range files {
f, _ := os.Open(file)
processFile(f)
f.Close() // close immediately after processing each file
}From the same buckets as this rule.
All static JS/CSS/font/image files MUST use content-hashed filenames (e.g., app.9c1a7b.js) and be served with "Cache-Control: public, max-age=31536000, immutable". HTML and other non-fingerprinted documents MUST be served with "Cache-Control: no-cache" (or equivalent) to enable conditional revalidation.