Rust

Clone vs Copy — When to Use Each

Stack-allocated primitives implement `Copy` (auto-duplicated). Heap-owning types like `String` and `Vec` only implement `Clone` (you must explicitly call `.clone()` to opt into the deep copy cost).

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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.

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SQL

Views and Materialized Views

A view is a named query — no data stored. A materialized view caches the result; refresh it on demand. Great for expensive joins or aggregations that don't need to be real-time.

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Rust

Arc<Mutex<T>> — Shared Mutable State

Share mutable data across threads: `Arc` for the shared ownership, `Mutex` for the synchronized access. Lock with `.lock().unwrap()`; the guard drops the lock on scope exit.

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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.

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Rust

zip / enumerate / chain

Three adapters that pair, index, and concatenate iterators. Every Rust developer reaches for them daily.

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Kotlin

also — Side Effect, Return Itself

`x.also { ... }` runs a side-effect block with `x` as `it` and returns `x` unchanged. Used for logging, debugging, or asserting mid-chain without breaking it.

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Java

Generic Class with Type Parameter

Stamp out type-safe containers and helpers — same class body, multiple element types. The `<T>` declaration is what makes it generic.

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HTML

Figure + Figcaption (Images, Code, Charts)

`<figure>` groups self-contained illustrative content with its caption. Use it for images, code blocks, charts, diagrams — anything that's referenced from the surrounding text but stands on its own.

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SQL

Moving Average (Window Frame)

Add a frame clause (`ROWS BETWEEN N PRECEDING AND CURRENT ROW`) to compute moving averages, sliding sums, rolling stats — anything that needs a bounded look-back.

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Bash

Run on Multiple Hosts via SSH (with progress)

Iterate a host list, run the same command on each, show colored OK/FAIL summary at the end. Useful for ad-hoc fleet operations without setting up Ansible.

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Kotlin

Custom Property Delegate

Any object with `getValue` / `setValue` operator methods can serve as a delegate. Lets you encapsulate cross-cutting behavior (logging, persistence, validation).

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Bash

PID File Management

Write a daemon's PID to a file at start, check on subsequent runs, clean up on exit. Avoids two copies of the same daemon when the script is invoked twice.

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PHP

CSV Writer with Proper Escaping

Write rows to a CSV file using fputcsv with sensible quoting. Also writes a UTF-8 BOM so Excel opens the file with the right encoding.

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Go

goroutine + sync.WaitGroup

`go fn()` spawns a goroutine. To wait for several to finish, use `sync.WaitGroup` — call `Add` before spawning, `Done` (deferred) inside, `Wait` to block until all are done.

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Kotlin

Local Functions

Functions can be declared inside other functions. Closures over outer scope let you eliminate parameter-threading. Use sparingly — too many nested locals hurts readability.

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HTML

Sortable Table (semantic markup + JS hook)

Use `<button>` inside `<th>` and `aria-sort` on the column so screen readers announce sort state. The button is the keyboard-accessible trigger; JS only handles the actual sort.

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TypeScript

useDebounce — Debounced State

A React hook that returns a debounced version of any value. Trigger expensive effects (search, autosave, network fetches) on this value instead of the raw input.

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Bash

Parse --flag=value Arguments

A getopts-free arg parser handling long flags, equals-separated values, and bundled short flags. Customize as needed.

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Bash

Most-Modified Files in Repo

Find the hottest files in a git history — useful for spotting hotspots that need refactoring or extra test coverage.

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Kotlin

Default Arguments + Named Parameters

Default values eliminate most overload sets. Named args make call sites self-documenting and let you skip middle parameters without thinking about positions.

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JavaScript

JSON Fetch Wrapper

A thin wrapper around fetch that automatically serialises the request body to JSON, sets the Content-Type header, parses the response as JSON, and throws a descriptive error on non-OK responses. Covers the boilerplate needed for 95% of REST API calls in a single reusable function.

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TypeScript

useFetch — Minimal Data Fetching Hook

A tiny self-contained data-fetching hook with loading/error/data states and AbortController cleanup on unmount. Good baseline before reaching for TanStack Query.

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Rust

Trait with Default Methods

A trait can supply default implementations — implementors override only the bits they need. Like abstract base classes, but with structural typing and zero runtime cost.

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HTML

Visually Hidden Utility (.sr-only)

Hides content from sighted users but keeps it discoverable by screen readers. Use for icon-only buttons, table-row context, and form-status announcements that don't need visible text.

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Go

Multiple Return Values + Named Returns

Go functions can return multiple values — most idiomatically a `(result, error)` pair. Named returns let you document the meaning of each value AND enable naked returns in short functions.

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Rust

Custom Iterator Implementation

Implementing `Iterator` is just supplying a `next() -> Option<Item>`. You automatically gain `map`, `filter`, `collect`, and every other adapter for free.

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SQL

ARRAY_AGG and JSON_AGG (PostgreSQL)

Roll up grouped rows into a PostgreSQL array or JSON array — often a faster replacement for the application doing the same "group children under parent" join.

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Java

Files.readString / readAllLines

`java.nio.file.Files` shipped these convenience helpers in Java 8/11. Way cleaner than the legacy `FileReader` + `BufferedReader` ceremony for small/medium files.

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Bash

Print a Boxed Banner

Wrap a string in a Unicode box for important headers. Auto-sizes to the longest line. Helps milestone messages stand out in long CI logs.

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