You can create multidimensional arrays by nesting pairs of square brackets, where the name of the base type of the elements is contained in the innermost pair of square brackets. function-type → attributes opt function-type-argument-clause throwsopt -> type, function-type-argument-clause → ( function-type-argument-list ...opt ), function-type-argument-list → function-type-argument | function-type-argument , function-type-argument-list, function-type-argument → attributes opt inoutopt type | argument-label type-annotation. This restriction helps Swift perform more of its checks for conflicting access to memory at compile time instead of at runtime. For example, the metatype of the class type SomeClass is SomeClass.Type and the metatype of the protocol SomeProtocol is SomeProtocol.Protocol. And SomeProtocol.self returns SomeProtocol itself, not an instance of a type that conforms to SomeProtocol at runtime. If you are not sure what number value a variable will be assigned in the program, you can specify it as Number type. Named types include classes, structures, enumerations, and protocols. According to IEEE, it has a 64-bit floating point precision. Opaque types appear as the return type of a function or subscript, or the type of a property. Data types that are normally considered basic or primitive in other languages—such as types that represent numbers, characters, and strings—are actually named types, defined and implemented in the Swift standard library using structures. For class instances, the initializer that’s called must be marked with the required keyword or the entire class marked with the final keyword. You can also name the elements of a tuple type and use those names to refer to the values of the individual elements. A function type represents the type of a function, method, or closure and consists of a parameter and return type separated by an arrow (->): The parameter type is comma-separated list of types. In a protocol declaration or a protocol member declaration, the Self type refers to the eventual type that conforms to the protocol. A compound type may contain named types and other compound types. Variables and Constants in Swift Explained. Float represents a 32-bit floating-point number. A metatype type refers to the type of any type, including class types, structure types, enumeration types, and protocol types. The Swift language defines the postfix ! Go to the Swift Sandbox. Classes can’t use an opaque type as the return type of a nonfinal method. A compound type is a type without a name, defined in the Swift language itself. What is the type of value? An opaque type defines a type that conforms to a protocol or protocol composition, without specifying the underlying concrete type. If the value is nil, no operation is performed and therefore no runtime error is produced. For example, you can assign values of implicitly unwrapped optionals to variables, constants, and properties of optionals, and vice versa. type → implicitly-unwrapped-optional-type. And so on. type-identifier. This means that in the example above, array3D[0] refers to [[1, 2], [3, 4]], array3D[0][1] refers to [3, 4], and array3D[0][1][1] refers to the value 4. type-annotation → : attributes opt inoutopt type. as syntactic sugar for the named type Optional, which is defined in the Swift standard library. For an example of an enumeration definition that uses a type inheritance clause to specify the type of its raw values, see Raw Values. He manages our C++ curriculum and was inspired by my Swift / Python comparison (Comparison of Python and Apple’s Swift Programming Language Syntax). In the following example, for instance, the explicit type annotation (: Float) on the constant eFloat causes the numeric literal 2.71828 to have an inferred type of Float instead of Double. A protocol composition type defines a type that conforms to each protocol in a list of specified protocols, or a type that is a subclass of a given class and conforms to each protocol in a list of specified protocols.