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#php
#kotlin
#bash
#go
#sql
#rust
#typescript
#html
#java
#python
#files
#utils
#strings
#http
#concurrency
#async
#json
#arrays
#security
#types
#crypto
#database
#dates
#format
Go
errgroup — Fan-Out with Cancellation
`golang.org/x/sync/errgroup` runs N goroutines, returns the first error, and cancels the others via a shared context. The right pattern for parallel I/O where any failure should abort the rest.
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Bash
Process Substitution Cheatsheet
`<(...)` makes a command's output look like a file; `>(...)` makes a command's input look like a file. Killer feature for tools that only accept filenames.
SQL
date_trunc — Bucket Times into Hours/Days/Weeks
`date_trunc('day', ts)` rounds a timestamp down to the start of the day. Use for time-series GROUP BYs — daily/weekly/hourly buckets without messy arithmetic.
Rust
zip / enumerate / chain
Three adapters that pair, index, and concatenate iterators. Every Rust developer reaches for them daily.
PHP
Detect & Strip Byte Order Mark
Some text editors prepend a UTF-8 BOM (0xEF 0xBB 0xBF) which breaks header() calls, JSON, and PHP output. Detect and strip it defensively when ingesting external files.
JavaScript
DOM Ready Helper
Runs a callback when the DOM is fully parsed and ready, without waiting for images or stylesheets. Works whether called before or after DOMContentLoaded has already fired — unlike a bare addEventListener which misses the event if the DOM is already ready when the script runs.
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.
Java
CountDownLatch — Wait for N Events
Block one or more threads until a count of events occurs. Set the count up front; each event calls `countDown()`; waiters call `await()`. Classic "wait until all workers are ready" pattern.
Python
JWT Sign + Verify (PyJWT)
The de-facto JWT library for Python. HS256 demo with an exp claim and the standard "verify everything" decode flow. Mind that PyJWT raises specific exceptions you can catch separately.
Python
asyncio.wait_for — Timeout Wrapper
Cancel a coroutine if it takes longer than `timeout` seconds. Raises asyncio.TimeoutError when fired so the caller can fall back. Python 3.11+ has asyncio.timeout() as a context-manager alternative.
PHP
Validate Email (RFC-aware)
Use PHP's built-in FILTER_VALIDATE_EMAIL with the FILTER_FLAG_EMAIL_UNICODE flag for IDN domains, plus a length sanity check. Trust this over hand-rolled regex.
PHP
Unique by Callback
Like array_unique, but the uniqueness test is a callback that returns the key to dedupe by. Useful for "unique by ID" or "unique by lowercased email" across arrays of objects/rows.
PHP
Word Count (UTF-8 aware)
Count words in a string in a way that works for any Unicode script — including those without ASCII whitespace. Built on the \p{L}\p{N} Unicode regex categories.
HTML
Textarea with Character Counter
Combine `maxlength` (hard cap) with a small JS-driven live counter. Browsers won't let users paste past `maxlength`, so this is purely UX feedback.
TypeScript
Deferred / Externally-Resolvable Promise
Create a Promise whose `resolve` and `reject` are exposed externally. Useful when you need to settle a promise from outside its executor — e.g. waiting on an event-driven response.
Java
CompletableFuture — Async Chains
`CompletableFuture` is the idiomatic way to compose async work. `thenApply` for sync transforms, `thenCompose` for async chains (flatMap), `exceptionally` for fallback on failure.
PHP
PDO Schema Existence Checks
Idempotent helpers to test whether a table, column, or index already exists — handy when writing your own migration runner without an ORM.