Kotlin

reified Type Parameters

In an `inline` function, a `reified` type parameter survives erasure — you can use `T::class`, `is T`, `as T` at runtime. The killer use-case for JSON parsers ("give me a List<User>").

3h ago 0

Kotlin

Variance — in vs out

`out T` (covariant) → producer of T; can be assigned to a wider type. `in T` (contravariant) → consumer of T; can be assigned to a narrower type. Without modifiers, generics are invariant (strict match).

3h ago 0

Rust

Newtype Pattern (zero-cost wrappers)

Wrap a primitive in a tuple struct to give it a distinct type identity at the type level — without runtime cost. Replaces "is this number a UserId or a PostId?" bugs.

3h ago 0

Kotlin

Type-Safe Builder DSL

`@DslMarker` + lambdas with receivers let you build statically-typed DSLs that look like declarative configuration. The HTML / Gradle Kotlin DSL style.

3h ago 0

Kotlin

tailrec — Tail-Call Optimization

Mark a recursive function `tailrec` and the compiler rewrites it as a loop — no stack frame per call, no StackOverflowError on deep recursion. Function must end with itself as the FINAL expression.

3h ago 0

Python

Walk Directory Tree (Filtered)

Recursively yield every file under a directory matching a predicate. Built on pathlib.rglob; the predicate gives you precise control without listing the whole tree up front.

3h ago 0

PHP

Dump Variable to Browser (var_dump replacement)

A nicer var_dump-style dumper that wraps output in <pre> with monospaced font for browser inspection. Drop-in replacement for var_dump while debugging.

3h ago 0

TypeScript

Type-Safe Event Emitter

A 30-line type-safe mini EventEmitter. The event-name → payload map is enforced at compile time, so emit and on calls can't drift apart.

3h ago 0

Bash

Cron Entry From Script

Append a cron job idempotently — grep first to avoid duplicates on re-run. Doesn't require editing files manually.

3h ago 0

Bash

Clean Up Merged Branches

Delete every local branch that's been merged to main. Filters out main/master and the current branch as a safety net.

3h ago 0

Kotlin

Lambdas and Function Types

Kotlin functions are first-class values. A lambda is `{ args -> body }`; its type is `(InputTypes) -> ReturnType`. Single-argument lambdas can use the implicit `it` parameter.

3h ago 0

Go

sync/atomic — Lock-Free Counter

For simple counters and flags, atomic ops are much faster than `sync.Mutex`. Go 1.19+ added typed wrappers (`atomic.Int64`) — clearer than the raw functions.

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

Bash

Check Command Exists Before Using It

`command -v` is the portable, fast way to check whether a binary is on $PATH. Avoid `which` (its behavior varies between systems).

3h ago 0

Kotlin

kotlinx-datetime — Multiplatform Dates

`kotlinx-datetime` is the multiplatform date/time library — works on JVM, JS, Native. `Instant` (UTC moment), `LocalDate`, `TimeZone` are the building blocks.

3h ago 0

Kotlin

Path Operations with java.nio.file

Modern Kotlin code uses `java.nio.file.Path` over the legacy `File`. Operator overloads + Kotlin extensions make it ergonomic.

3h ago 0

TypeScript

Conditional Types Basics

`T extends U ? X : Y` lets types branch on shape. Combine with `infer` to extract pieces of complex types — the building block under `ReturnType`, `Parameters`, and most utility libraries.

3h ago 0

Kotlin

Parameterized Tests with JUnit 5

JUnit 5 + Kotlin: `@ParameterizedTest` runs the same test body with multiple input rows. `@CsvSource` for inline data, `@MethodSource` for complex args.

3h ago 0

Bash

docker exec — Drop Into Running Container

`docker exec` is your debugger. Get a shell, inspect env, tail logs, run one-off commands inside a live container.

3h ago 0

Bash

Disk Space Alert

Cron-friendly script that checks disk usage on each filesystem and emails (or webhooks) if any partition exceeds a threshold.

3h ago 0

SQL

CREATE TABLE with Constraints

Declare data integrity rules right in the schema — primary keys, foreign keys, unique constraints, NOT NULL, CHECK constraints, defaults. The DB enforces them so application bugs can't corrupt your data.

3h ago 0

Bash

Rotate Logs Manually

If a service doesn't hook into logrotate, you can still rotate a log file yourself in one safe pattern: rename current → .1, truncate the original, signal the process to re-open if needed.

3h ago 0

Go

errors.Join — Aggregate Multiple Errors

Go 1.20+ ships `errors.Join`, which combines multiple errors into one. Stop accumulating errors in a slice and stringifying yourself — use the standard library.

3h ago 0

Go

Variadic Functions

`...T` in the last parameter slot accepts zero or more T values. Pass a slice by suffixing with `...` to spread it. Used everywhere from `fmt.Println` to custom builders.

3h ago 0

Bash

Download with Progress Bar

Show a progress bar for long downloads. wget gives a great built-in bar; curl needs an explicit flag.

3h ago 0

PHP

Recursive Directory Walker

Yield every file under a directory using a generator and SPL's RecursiveIteratorIterator. Filter by extension or any other predicate without slurping all paths into memory first.

3h ago 0

Go

Signal Handling with signal.NotifyContext

Go 1.16+ `signal.NotifyContext` returns a context that's canceled on the listed signals. Cleaner than the legacy `signal.Notify(channel)` dance for graceful shutdown.

3h ago 0

Bash

Tar Archive with Timestamp

Pack up a directory with a date-stamped filename for easy backups. -z for gzip, -j for bzip2, -J for xz (smallest, slowest).

3h ago 0

PHP

Generate Identicon Avatar

Render a deterministic 5x5 symmetric "identicon" placeholder avatar from any seed (usually a user's email or username). No external service — pure GD.

3h ago 0

Go

database/sql — Open + Query

`database/sql` is driver-agnostic — pick a driver (`pgx/stdlib`, `go-sql-driver/mysql`, `mattn/sqlite3`). Always `defer db.Close()` only on app exit; the pool is meant to be long-lived.

3h ago 0