Go basic types and zero values: meaning and behaviour

Direct Answer

Every variable in Go has a defined value even when no explicit initializer is written. Numbers start at 0, booleans at false, strings at an empty string, and pointers, slices, maps, channels, functions, and interfaces at nil. Arrays and structs are zeroed recursively. Good Go types often make their zero value useful, but nil reference-like values do not all behave the same way.

Deep Dive & Architecture

For an unexpected zero or nil panic, identify whether the value was never assigned, deliberately reset, or missing from decoded input.

Then check the exact operation that requires initialization.

Check map writes, channel sends, pointer dereferences, interface values, and serialization differences between nil and empty collections. Test the untouched zero state, the first mutation, missing input, and any JSON or database boundary where nil and empty have different meaning.

A common mistake is assuming every nil value behaves like an empty initialized value. Reading a missing key from a nil map is safe, but writing to that map panics; appending to a nil slice is safe. Know the zero value of each field, initialize maps and channels before use, and model optional business data with an explicit presence flag or pointer when zero is meaningful.

Code Example

var count int       // 0
var ready bool      // false
var name string     // ""
var items []string  // nil, append works
var users map[string]int // nil, writes panic

Common Mistakes & Pitfalls

Listing syntax without explaining what the program stores or does.