ADR 0011: Type syntax: generics-style collections, loose `?`

Status: Accepted; List<T> superseded by 0023; Map<K, V>, Chan<T>, <T>, and PascalCase primitive names superseded by 0031

Context

Postfix ? on Go’s prefix type syntax is ambiguous ([]*User?), and Kotlin-like generic syntax was requested.

Decision

List<T>, Map<K, V>, Chan<T> for slices, maps, and channels. [N]T for arrays, *T for pointers, (A) -> R [throws] for functions. ? applies to the whole type it follows (*User? = nullable pointer). Type arguments are explicit scopes (List<*User?>). Primitive names are PascalCase (Int64, String, Error, Any).

Alternatives

• Go type syntax ([]T, map[K]V): familiar to Go users, but forces precedence rules for ? that make the common case awkward.
• T[] (TypeScript): same ambiguity, and no map counterpart.
• Slice<T>: accurate, but unfamiliar. List is what most developers reach for. The docs state plainly that it is a Go slice.

Consequences

Unambiguous nullability in nested types. < > in expression position need speculative parsing for explicit type arguments (rare, planned). Go programmers learn a small rename table (language.md §8.1).