Tags
#php
#kotlin
#bash
#go
#sql
#rust
#typescript
#html
#java
#python
#files
#utils
#strings
#http
#concurrency
#async
#json
#arrays
#security
#types
#crypto
#database
#dates
#format
Java
Wildcards — extends vs super (PECS)
Producer-Extends, Consumer-Super. `? extends T` is read-only (you can take items OUT). `? super T` is write-only (you can put items IN). Lets generic APIs accept a wider range of types.
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Java
Text Blocks (Java 15+)
Multi-line string literals with proper indentation handling. Stop concatenating newlines by hand. The compiler removes the common leading whitespace automatically.
Bash
Hash File (SHA-256)
Compute and verify file checksums for downloads, backups, and integrity audits. sha256sum on Linux; shasum -a 256 on macOS.
Bash
Format Date Like a Pro
`date` accepts a format string + optional override of the date being formatted. The +%FT%TZ form gives you ISO-8601 / RFC-3339 in one call.
PHP
Recursively Delete Directory
Remove a directory and everything under it. Defensive against symlinks (unlinks the symlink rather than recursing into it). Returns the count of items removed.
PHP
Email Address Obfuscator
Render an email address as HTML that is human-readable but resistant to naive scraping bots. Uses entity encoding and an optional Caesar-style ROT for the mailto link.
JavaScript
Download File from Client
Programmatically triggers a file download from a Blob, File object, or plain text/JSON string without a server round-trip. Creates a temporary anchor element with a download attribute and revokes the object URL after use to prevent memory leaks. Supports custom filenames and MIME types.
JavaScript
Simple State Machine
A lightweight finite state machine that defines valid states and allowed transitions between them. Attempting an invalid transition throws an error. Supports entry/exit hooks per state for side effects. Useful for modelling UI flows (idle → loading → success/error), auth states, and multi-step forms.
JavaScript
Format Currency
Formats a number as a locale-aware currency string using the built-in Intl.NumberFormat API. Supports any ISO 4217 currency code and any BCP 47 locale tag. No external library required — handles symbol placement, thousands separators, and decimal places automatically per locale rules.
JavaScript
Event Emitter (Pub/Sub)
A lightweight publish/subscribe event system. Listeners register with on(), fire once with once(), are removed with off(), and events are dispatched with emit(). Useful for decoupling modules, building plugin systems, and implementing the Observer pattern without a framework dependency.
JavaScript
Delegate Event Listener
Attaches a single event listener to a parent element and handles events from matching descendant elements via event delegation. More efficient than attaching listeners to many individual elements, and works for elements added dynamically to the DOM after the listener is registered.
Kotlin
java.time — When You Need JVM Interop
On the JVM, `java.time` is fine — and often necessary for interop with Java APIs. Kotlin's extension methods make it ergonomic enough that you might never reach for kotlinx-datetime.
Kotlin
associate and associateBy
`associateBy` builds a `Map<K, T>` keyed by a derived value. `associateWith` keys by the items themselves with derived values. `associate` lets you build both key and value from each item.
Kotlin
Extension Properties
Like extension functions, but as a property. Must have a custom getter (and optionally a setter) since extensions can't have backing fields. Reads like a real property at the call site.
SQL
Array Columns (PostgreSQL)
Native array columns avoid an extra join for "small list of things per row" patterns — tags, categories, allowed_roles. Combine with GIN index for fast `@>` / `&&` operators.
SQL
DELETE with JOIN / USING
Delete rows from one table conditional on a related table. PostgreSQL uses `USING`; MySQL uses join syntax in the DELETE. Run as a SELECT first to verify what you're about to remove.
Go
Concurrency Limit via Buffered Channel (Semaphore)
A buffered channel of size N is the simplest semaphore in Go — acquire by sending, release by receiving. Zero dependencies, no sync.Semaphore needed.