Swift literals

The so-called literal refers to a value such as a specific number, string, or Boolean value that can directly indicate its type and assign a value to a variable. For example, below:

let aNumber = 3         //整型字面量
let aString = "Hello"   //字符串字面量
let aBool = true        //布尔值字面量

Integer literal

An integer literal can be a decimal, binary, octal or hexadecimal constant. The binary prefix is 0b, the octal prefix is 0o, the hexadecimal prefix is 0x, and the decimal has no prefix:

The following are some examples of integer literals:

let decimalInteger = 17           // 17 - 十进制表示
let binaryInteger = 0b10001       // 17 - 二进制表示
let octalInteger = 0o21           // 17 - 八进制表示
let hexadecimalInteger = 0x11     // 17 - 十六进制表示

Floating point Type literal

Floating point literal has an integer part, a decimal point, a decimal part and an exponent part.

Unless otherwise specified, the default derivation type of floating-point literals is Double in the Swift standard library type, which represents a 64-bit floating point number.

Floating point literals are expressed in decimal by default (without prefix), and can also be expressed in hexadecimal (with the prefix 0x).

A decimal floating-point literal consists of a decimal digit string followed by a decimal part or an exponent part (or both). The decimal part consists of a decimal point . followed by a string of decimal digits. The exponent part consists of an uppercase or lowercase letter e prefixed by a string of decimal digits that represents the power of 10 multiplied by the quantity before e. For example: 1.25e2 means 1.25 ⨉ 10^2, which is 125.0; similarly, 1.25e-2 means 1.25 ⨉ 10^-2, which is 0.0125.

A hexadecimal floating-point literal consists of a prefix 0x followed by an optional hexadecimal fractional part and a hexadecimal exponent part. The hexadecimal fraction consists of a decimal point followed by a string of hexadecimal digits. The exponent part consists of an uppercase or lowercase letter p prefixed by a string of decimal digits that represents the power of 2 multiplied by the quantity preceding p. For example: 0xFp2 means 15 ⨉ 2^2, which is 60; similarly, 0xFp-2 means 15 ⨉ 2^-2, which is 3.75.

Negative floating-point literals consist of the unary operator minus sign - and a floating-point literal, for example -42.5.

Floating-point literals allow the use of underscores _ to enhance the readability of numbers. Underscores will be ignored by the system and therefore will not affect the value of the literal. Similarly, you can add 0 in front of a number and it will not affect the value of the literal.

The following are some examples of floating point literals:

let decimalDouble = 12.1875       //十进制浮点型字面量
let exponentDouble = 1.21875e1    //十进制浮点型字面量
let hexadecimalDouble = 0xC.3p0   //十六进制浮点型字面量

String literals

String literals are enclosed in double quotes It consists of a string of characters in the following format:

"characters"

String literals cannot contain unescaped double quotes ("), unescaped backslashes (\), carriage returns or line feeds symbol.

##\'Single quotation mark\"Double quotes\000Any character represented by 1 to 3 octal numbers \xhh...Any character represented by 1 to 2 hexadecimal digits

Transfer characters	Meaning
\0	Null character
\\	Backslash\
\b	Backspace (BS), moves the current position to the previous column
\f	Page change (FF), moves the current position to the beginning of the next page
\n	Line feed character
\r	Carriage return character
\t	Horizontal tab Symbol
\v	Vertical tab character

The following is a simple example of a string literal:

import Cocoa

let stringL = "Hello\tWorld\n\nphp中文网官网：\'http://www.php.cn\'"
print(stringL)

The execution result of the above program is:

Hello	World

php中文网官网：'http://www.php.cn'

Boolean literal

The default for Boolean literal The type is Bool.

Boolean literals have three values, which are Swift’s reserved keywords:

#true
means true.
means false.
##nil

← Swift constants

Swift operators →