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#php
#kotlin
#bash
#go
#sql
#rust
#typescript
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Kotlin
Coroutines — suspend Function Basics
`suspend fun` can be paused and resumed without blocking a thread. Call only from another `suspend` function or a coroutine builder (`launch`, `runBlocking`, `async`).
@admin
Kotlin
minOf / maxOf / sumOf / averageOf
Numerical reducers with a selector lambda — much cleaner than `.map { ... }.max()` chains. `sumOf` is type-aware (returns Int, Long, Double, BigDecimal as appropriate).
TypeScript
invariant() — Always-On Assertion
Throw if a condition is false, with TypeScript narrowing the type afterwards. Replaces ad-hoc `if (!x) throw` ladders and gives you type-safe guards in one line.
Go
context.WithValue — Request-Scoped Values
Attach data to a context that flows down through your call chain — request IDs, authenticated user, trace spans. Use a private key type to avoid collisions across packages.
Go
SHA-256 Hash of File or String
`crypto/sha256` is the canonical hash. Use the streaming `Hash` interface for files — never load multi-GB content into memory just to hash it.
Bash
Check If Array Contains Element
A pure-bash membership test using `=~` or by iterating. Both are useful — pick by readability vs. speed.
Rust
CSV Read/Write with the csv Crate
`csv` + `serde` lets you read/write CSVs directly into typed structs. No manual field parsing; column order tolerant via headers.
Kotlin
distinct, distinctBy, intersect, union
Set-style ops on collections. `distinct` removes duplicates; `distinctBy` lets you key the dedupe by a derived value; `union/intersect/subtract` give you set operations.
Kotlin
Sequences — Lazy Collections
A `List` materializes every intermediate `map`/`filter` result. A `Sequence` processes ONE element through the whole pipeline at a time — better for big inputs or short-circuiting (`first`, `take`).
HTML
Select with Optgroup
`<optgroup label="...">` visually groups options inside a `<select>`. Renders as a non-selectable header in every browser; screen readers announce the group as context.
Go
Pointers — When and Why
Use pointers when you want to mutate the callee's value, share a large struct without copying, or distinguish "no value" via nil. Go has no pointer arithmetic — much safer than C.
TypeScript
groupBy (with key callback)
Group a list into a record keyed by whatever the callback returns. Like Lodash _.groupBy or the new Object.groupBy in modern runtimes. Generic enough to handle string, number, or symbol keys.
Go
Table-Driven Tests with t.Run
A table of test cases looped through `t.Run` gives every case its own name in the output, makes adding new cases trivial, and lets you run individual cases with `-run TestX/case_name`.
Kotlin
map / filter / reduce
The three classic functional combinators. Each takes a lambda and returns a new collection (or a single value for reduce). Chain freely — intermediate allocations only matter at very large scale (use `Sequence` then).
Go
CSV Read/Write with encoding/csv
`encoding/csv` parses RFC 4180 CSVs. Read row-by-row with `Read()` or all at once with `ReadAll()`. Same for writing — flush with `Writer.Flush()` before closing.
Kotlin
windowed and chunked
`chunked(n)` splits a list into NON-overlapping pieces of size n. `windowed(n)` slides a fixed-size window across — overlapping. Useful for moving averages, n-grams, batch APIs.
Kotlin
fold and scan
`fold` accumulates from a seed across all items. `runningFold` / `scan` yields every intermediate accumulator value — running totals, cumulative metrics.