Rust

Move vs Borrow — the Core Rule

Rust's ownership model: passing a value transfers ownership (move); taking a `&value` lets you read without taking ownership; `&mut value` lets you modify without taking ownership. Only one mutable borrow OR many immutable borrows at a time.

2h ago 0

TypeScript

useMediaQuery — Responsive Hook

Subscribe to a CSS media query (e.g. dark mode, viewport size) from React. Re-renders when the match changes. SSR-safe — returns `false` on the server.

2h ago 0

Python

TypedDict for JSON API Shapes

When you parse JSON, you want types — but creating a class for every payload is overkill. TypedDict gives you the static-checking benefits without the runtime overhead, and `total=False` marks every field optional.

2h ago 0

Python

NewType for Nominal IDs

Python's type system is structural — `UserId` and `PostId` are both just `int` unless you ask otherwise. `NewType` creates a distinct type with zero runtime cost for static checking only.

2h ago 0

HTML

Responsive Image — srcset + sizes

Let the browser pick the right image for the viewport. `srcset` lists candidates by intrinsic width; `sizes` tells the browser how big the image will render. Cuts mobile data dramatically.

2h ago 0

Java

try-with-resources

For any `AutoCloseable` (files, streams, DB connections, locks), declare it in `try(...)` and Java auto-calls `close()` even on exception. Replaces error-prone `try / finally` blocks.

2h ago 0

HTML

Responsive Table — Scroll on Mobile

Wrap any wide table in a horizontally-scrolling container. The table itself stays semantic (no display:block hacks that break screen readers); only the wrapper scrolls.

2h ago 0

Rust

Box<dyn Error> — Quick Boxed Errors

If you don't want the thiserror/anyhow dependency, `Box<dyn std::error::Error>` works as a catch-all. The `?` operator promotes any concrete error via `From`.

2h ago 0

Java

Multi-Catch + Exception Chaining

Catch several unrelated exception types in one block with `|`. Re-throw with `cause` to preserve the stack trace and underlying error.

2h ago 0

Java

Virtual Threads (Java 21+)

Java 21's virtual threads are millions-of-them cheap — JVM multiplexes them onto a small carrier pool. Replaces async/reactive code for most I/O-bound workloads: just write blocking code that doesn't actually block a kernel thread.

2h ago 0

Rust

Custom Error Type with thiserror

The `thiserror` crate generates a clean `Error + Display + Debug` impl from an enum, with automatic `From` conversions. The library-author's error-type tool of choice.

2h ago 0

Kotlin

Custom Exception + Sealed Result Pattern

For library / service code, define your own exception hierarchy. Pair with `sealed` + `when` for type-safe error handling at the call site.

2h ago 0

HTML

Multi-Column Footer

Standard site footer with grouped links, brand block, social icons, and legal/copyright. Use semantic `<nav aria-label>` on each column so screen readers announce the section labels.

2h ago 0

Java

Sealed Classes + Pattern Matching (Java 21+)

`sealed` restricts which classes can extend a type — perfect for closed hierarchies that pattern matching can switch over exhaustively. The compiler enforces that you handle every variant.

2h ago 0

PHP

Sort by Multiple Keys

Stable multi-column sort for arrays of associative rows. Each column can be sorted ASC or DESC independently. Wraps usort with a chained comparator.

2h ago 0

Rust

Lifetime Annotations Basics

Lifetimes are how Rust proves references don't outlive what they point to. Most are inferred — but functions returning references from arguments need explicit `'a` to relate input and output.

3h ago 0

PHP

Index Array By Column

Rekey a list of rows by one of their column values, so $byId[42] gives the row with id=42. Equivalent to array_column($rows, null, $key).

3h ago 0

Bash

Source Multiple Files from Directory

A common ~/.bashrc / ~/.zshrc pattern: split your config into ~/.bashrc.d/*.sh and source them all. Easier than one giant file.

3h ago 0

Bash

Sort an Array

Bash itself doesn't sort arrays — you pipe through `sort`. readarray captures the sorted output back into an array, preserving each element verbatim (including spaces).

3h ago 0

SQL

Gap Detection — Missing Days / Sequences

Find holes in a series — missing invoice numbers, days with no events, gaps in a sequence. Combine `LAG` (or `generate_series`) with a join to spot them.

3h ago 0

Python

Stdlib .env Loader (no dependency)

Parse a `.env` file into a dict and optionally export to os.environ. Skips comments and blank lines, strips surrounding quotes — no python-dotenv dependency needed.

3h ago 0

SQL

Pivot Without PIVOT (Conditional Aggregation)

Most databases don't have a real `PIVOT` keyword (SQL Server does). The portable answer is conditional aggregation — `SUM(CASE WHEN ...) AS col` for each pivoted value.

3h ago 0

Python

argparse with Subcommands

Standard-library CLI framework. Subcommands (like `git COMMAND`) require a sub-parser per command, each with its own arguments and handler.

3h ago 0

SQL

STRING_AGG / GROUP_CONCAT

Concatenate values across a group into a single delimited string. PostgreSQL/MSSQL use `STRING_AGG`; MySQL uses `GROUP_CONCAT`; SQLite has both.

3h ago 0

Go

maps package — Modern Helpers

`maps` (Go 1.21+) adds Keys, Values, Equal, Clone, Copy — replaces the slice-of-keys boilerplate you used to write to iterate a map deterministically.

3h ago 0

SQL

ROLLUP — Subtotals and Grand Totals

`GROUP BY ROLLUP` adds subtotal rows (with NULL for the rolled-up columns) plus a grand total. Drop into reports without writing UNIONs by hand.

3h ago 0

SQL

SELECT DISTINCT and Counting Uniques

`DISTINCT` removes duplicate rows. Combine with `COUNT(DISTINCT col)` to count uniques in aggregations — different from `COUNT(*)`.

3h ago 0

SQL

Sessionization — Group Events into Sessions

Stitch a stream of events into "sessions" where events more than N minutes apart start a new session. Uses LAG + a SUM-OVER trick to assign session IDs.

3h ago 0

SQL

Cohort Retention Analysis

Group users by their signup week, then count how many were still active in each subsequent week. The classic SaaS retention table — entirely in SQL.

3h ago 0

Bash

Idempotent Append to File

Add a line to a file (e.g., a config or PATH export) only if it isn't already present. Common in install/setup scripts that need to be safe to re-run.

3h ago 0