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#php
#kotlin
#bash
#go
#sql
#rust
#typescript
#html
#java
#python
#files
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#http
#concurrency
#async
#json
#arrays
#security
#types
#crypto
#database
#dates
#format
SQL
Transactions and Isolation Levels
Wrap related changes in a transaction so they commit or roll back together. Isolation levels trade consistency for concurrency — pick the weakest one that meets your correctness needs.
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PHP
Detect MIME Type via Magic Bytes
Use PHP's built-in finfo (libmagic) to detect a file's true MIME type from its bytes — not from the extension, which can be lied about. Critical for validating user uploads.
Kotlin
flatMap and Flattening
`flatMap` maps each item to a collection, then concatenates. Use it when "for each X, produce N Y's, collect all Y's". `flatten()` is the no-mapping version.
Kotlin
Immutable vs Mutable Collections
`listOf` / `setOf` / `mapOf` build READ-ONLY views; `mutableListOf` / `mutableSetOf` / `mutableMapOf` are mutable. Default to immutable — the call site is a contract about intent.
PHP
Parse Query String Without Mangling
PHP's parse_str converts dots/spaces in keys to underscores. This alternative preserves them — important when parsing third-party query strings (e.g., webhook payloads).
Go
HTTP Middleware (Decorator Pattern)
Middleware in Go is `func(http.Handler) http.Handler`. Wrap a handler with logging, auth, recovery, CORS, or rate limiting — chain them together for a real middleware stack.
Go
Generic Result / Option Type
Go doesn't have built-in Result types, but generics make them ergonomic. Combine with `errors.Is` and you have type-safe railroaded error handling.
Kotlin
Channel — Coroutine Communication
A `Channel<T>` is a coroutine-safe queue — producer side sends, consumer side receives. Bounded buffer applies backpressure. Use Flow when broadcasting; use Channel for hand-off between coroutines.
Python
Result / Either with Generics
Encode "this might fail" in the type signature instead of throwing. Python 3.12+ generics syntax keeps it compact. Forces the caller to handle the failure branch.
JavaScript
IndexedDB Wrapper
A Promise-based wrapper for the IndexedDB API — simplifies the verbose request/onsuccess/onerror pattern into clean async/await calls. Supports get, set, delete, and getAll operations on a named object store. Ideal for storing large client-side datasets, offline data, and blobs that exceed localStorage limits.
Java
Collectors.partitioningBy — Split by Predicate
Special case of groupingBy when the key is boolean — returns a `Map<Boolean, List<T>>` for the "true" and "false" buckets. Slightly more efficient than groupingBy.
Go
text/template — Simple Templating
Stdlib templating with `{{.Field}}` placeholders, range loops, if/else, and function pipelines. Safe alternative for non-HTML text (e.g. emails, config files).
Python
AES-GCM Encrypt / Decrypt (cryptography)
Authenticated symmetric encryption using AES-256-GCM from the `cryptography` package. Stores nonce + ciphertext + tag together as base64 so storage is a single column.
Python
unique_everseen — Order-Preserving Dedupe
Remove duplicates while preserving original order (set() loses order on collisions). Optional key function lets you dedupe by a derived value — e.g., lowercased email.
TypeScript
Promise.allSettled — Typed Results
`Promise.all` rejects on the first failure; `allSettled` waits for every promise and gives you per-promise status. Pair with a type guard to split fulfilled from rejected.
PHP
JSON Lines (NDJSON) Stream Reader
Read newline-delimited JSON (one object per line) as a generator. Each yield gives you the next decoded record without holding the whole file in memory.
Kotlin
Property Delegation by Map
Delegate a property to a `Map<String, V>` — reading the property fetches by name; writing stores by name. Quick way to back a class with a config map.