Nil & Optional
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nil represents the absence of a value. A type that may be nil is an
optional; the nil-safety operators (?., ??) — covered in Operators — let
you work with them without crashing:
nil alongside the booleans; optional handling lives in the Operators chapter.
04-bool-and-nil.zolo
// Feature: bool, nil, optional `T?`
// Syntax: `true` / `false` / `nil`; `T?` for optional types
// When to use: boolean logic; `nil` for "absence"; `T?` for values
// that may be missing in the type system.
// Booleans.
let active = true
let done: bool = false
// Short-circuit in && and ||
let a = active && 1 < 2 // true
let b = done || 1 == 1 // true
print(a, b)
// Logical negation.
print(!active) // false
// `nil` is the "empty" value — the only value of its type.
let nothing = nil
print(nothing) // nil
// Truthiness: only `nil` and `false` are falsy. 0, "", []
// COUNT as truthy (Lua semantics).
if 0 { print("0 is truthy") }
if "" { print("empty string is truthy") }
if [] { print("empty array is truthy") }
// Optional: `T?` accepts `T` OR `nil`.
let name: str? = nil
if name == nil {
print("no name")
}
// Use `??` for fallback.
let display = name ?? "anonymous"
print(display) // anonymous
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