The so-called literal, refers to as a specific number, string, or Boolean value this can be pointed directly to the local own type and value for the variable assignment. For example, in the following:
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 literals can be a decimal, binary, octal or hexadecimal constants. Binary prefix 0b, octal prefix 0o, hexadecimal prefix 0x, decimal values have no prefix:
Following is 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
Float literals have an integer part, a decimal point, and the fractional part of an exponent part.
Unless otherwise specified, the default type of floating-point literal derivation of Swift standard library types Double, 64-bit floating-point representation.
Float literals default decimal representation (no prefix), you can also use hexadecimal (prefix 0x).
Decimal floating-point literal string of digits followed by a decimal or fractional part of an exponent part (or both) components. Decimal part of the decimal point followed by a decimal digit string components. Exponent part by the uppercase or lowercase letter e is prefix followed by a decimal digit string consisting of this string of numbers represents the number of e multiplied several times before the parties 10. For example: 1.25e2 represents 1.25 ⨉ 10 ^ 2, that is, 125.0; similarly, 1.25e-2 represents 1.25 ⨉ 10 ^ -2, which is 0.0125.
Composition hexadecimal floating-point literals by the prefix 0x followed by an optional decimal part and hexadecimal hexadecimal exponent part. Hexadecimal fractional part of a decimal point followed by a string of hexadecimal numbers composed. Exponent part by the uppercase or lowercase letters p as a prefix followed by a decimal digit string composed of string which indicates the number of p multiplied several times before the party 2. For example: 0xFp2 represents 15 ⨉ 2 ^ 2, that is, 60; similarly, 0xFp-2 represents 15 ⨉ 2 ^ -2, which is 3.75.
Negative floating-point literal consists of a unary minus - and floating-point literals composed, for example, -42.5.
Floating-point literal underscore _ to allow the use of enhanced digital readability, underscores are ignored by the system, it will not affect the value of the literal. Similarly, you can also add 0 before the number, and 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
By a string literal is enclosed in double quotation marks in a string of characters, the form is as follows:
String literals can not contain unescaped double quotes ( "), did not escape the backslash (\), a carriage return or line feed.
|\ 0||Null character|
|\ B||Backspace (BS), the current position to the previous one|
|\ F||Form feed (FF), the current position to the beginning of the next page|
|\ R||Carriage return|
|\ T||Horizontal tab|
|\ V||Vertical tab|
|\ "||Double quotes|
|\ 000||Any character 1-3 octal number represented|
|\ Xhh ...||1-2 hexadecimal character represents any|
Following is a simple example of a string literal:
import Cocoa let stringL = "Hello\tWorld\n\n本教程官网：\'http://www.w3big.com\'" print(stringL)
The above program execution results:
Hello World 本教程官网：'http://www.w3big.com'
The default type Boolean literal is Bool.
Boolean literal value has three values, which are reserved keywords Swift:
- true true representation.
false false representation.
nil means no value.