Go

Fixed-length arrays in Go, value semantics, range iteration, compiler representation, literal initialization, and bounds checking.

1. What is a slice A dynamically growable array 2. Why slices are needed Arrays have a fixed number of elements and cannot grow dynamically 3. How to use slices 3.1. Basic usage 3.2. Function parameters pass the slice descriptor - although changes to the backing array are visible, append may replace the backing array, so return the slice when needed 3.3. nil slice and empty slice

What defer is, why it is used, cleanup patterns, interaction with return values and closures, LIFO ordering, recover, and its historical runtime implementation.

Goroutine context, deadlines, cancellation signals, request-scoped data, Context/canceler implementations, WithCancel/WithTimeout/WithValue, and references.

What sync.WaitGroup is, an example of waiting for goroutines, and its counter-based Add, Done, and Wait behavior.

An overview of the synchronization primitives provided by Go's sync package and links to Mutex, RWMutex, Cond, Once, Map, Pool, WaitGroup, and atomic.

What sync.Map is, concurrency-safety approaches, usage, its read/dirty data structures, and a summary of Load, Store, Delete, and dirty-to-read promotion.

What sync.Pool is, why temporary object caching can reduce allocation and GC pressure, usage, fmt integration, source structures, Get/Put, GC cleanup, and summary.

What select is, basic usage, random selection, empty select, nil channels, for-select exit, timeouts, quit channels, internals, and references.

What sync.Once is, singleton usage, its atomic+Mutex implementation, and a modified version that returns an error.