Types

A type determines the set of values together with operations and methods specific to those values. A type may be denoted by a type name, if it has one, or specified using a type literal, which composes a type from existing types.

Type      = TypeName | TypeLit | "(" Type ")" .
TypeName  = identifier | QualifiedIdent .
TypeLit   = ArrayType | StructType | PointerType | FunctionType | InterfaceType | SliceType | MapType | ChannelType .

Named instances of the boolean, numeric, and string types are predeclared. Other named types are introduced with type declarations. Composite types—array, struct, pointer, function, interface, slice, map, and channel types—may be constructed using type literals.

Each type T has an underlying type: If T is one of the predeclared boolean, numeric, or string types, or a type literal, the corresponding underlying type is T itself. Otherwise, T's underlying type is the underlying type of the type to which T refers in its type declaration.

type (
    A1 = string
    A2 = A1
)

type (
    B1 string
    B2 B1
    B3 []B1
    B4 B3
)

The underlying type of string, A1, A2, B1 and B2 is string. The underlying type of []B1, B3, and B4 is []B1.