Structures

An associated type declaration.

A class declaration.

A conditional compilation block declaration.

A class deinitializer declaration.

An enumeration declaration.

An extension declaration.

A function declaration.

An import declaration.

An initializer declaration.

An operator declaration.

An operator precedence group declaration.

A protocol declaration.

A structure declaration.

A subscript declaration.

A type alias declaration.

A declaration for a property or a top-level variable or constant.

A declaration attribute.

Attributes provide additional information about a declaration. For example, the @discardableResult attribute indicates that a function may be called without using the result.

A generic parameter.

A generic type or function declaration includes a generic parameter clause, consisting of one or more generic parameters enclosed by angle brackets (<>). Each generic parameter has a name, and may also specify a type constraint. For example, the following structure declaration has two generic parameters:

struct S<T, U: Equatable>

• The first generic parameter is named "T" and has no type constraint.
• The second generic parameter is named "U" and a type constraint on "Equatable".

A generic requirement.

A generic type or function declaration may specifying one or more requirements in a generic where clause before the opening curly brace ({) its body. Each generic requirement establishes a relation between two type identifiers.

For example, the following declaration specifies two generic requirements:

func difference<C1: Collection, C2: Collection>(between lhs: C1, and rhs: C2) -> [C1.Element]
   where C1.Element: Equatable, C1.Element == C2.Element

• The first generic requirement establishes a conformance relation between the generic types identified by "C1.Element" and "Equatable"
• The second generic requirement establsihes a sameType relation between the generic types identified by "C1.Element" and "C2.Element"

A declaration modifier.

A declaration may have one or more modifiers to specify access control (private / public / etc.), declare a type member (class / static), or designate its mutability (nonmutating). A declaration modifier may specify an additional detail within enclosing parentheses (()) following its name.

For example, the following property declaration has two modifiers:

public private(set) var title: String

• The first modifier has a name equal to "public", and a nil detail
• The second modifier has a name equal to "private" and a detail equal to "set"