Wind notes-swift programming language: point11~15

Catalog Index

Breeze Annotated-swift programming language

Point 11.

Numeric type literal

code Example:

 -           // decimalBinaryinteger = 0b10001       //  binaryoctalinteger = 0o21           // Eight- binary 0x11     // 16 binary

Annotations:

• The integer number of polygons can be written: decimal number, no prefix, binary number, prefix is 0b, octal number, prefix is 0o, hexadecimal number, prefix is 0x.
• The floating-point literal can be either decimal (without a prefix) or hexadecimal (the prefix is 0x).
• Floating point literals must have at least one decimal digit (or hexadecimal number) on either side of the decimal point.
• Decimal floating-point literals have an optional exponent, specified by uppercase or lowercase e.
• Hexadecimal floating-point literals must contain exponents, specified by uppercase or lowercase p.

• 17.2e0        // 17.2 of decimal floating-point numbers 0x11. 2p0  //  hex Floating-point 17.125

• If the exponent of a decimal number is exp, that number is equal to the product of cardinality and 10^exp.
• If the exponent of a hexadecimal number is exp, that number is equal to the product of cardinality and 2^exp.
• Integer and floating-point literals can include additional formatting (0 and underscore) to enhance readability, and these formats (0 and underscore) do not affect the actual value of the literal.

• 000123.456== 1_000_000.000_000_1

Point 12.

Numeric type conversions

code Example:

Let twothousand:uint16 =1= Twothousand + UInt16 (one)  

Annotations:

• In general, use the Int type, even if the integer constants and variables in your code are known to be non-negative.
• Using the default integer type guarantees that integer constants and variables can be reused directly, and can match the type inference of integer class literals.
• Using a type with an explicit length specifies that a value overflow can be found in time and implies that special data is being processed.
• Variables and constants of different integer types can store numbers of different ranges.
• If the number exceeds the constant or variable can be stored in the range, the compile time will be error.
• Because each integer type can store different ranges of values, you must selectively use numeric type conversions, depending on the situation.
• By selectively using type conversions, you can prevent implicit conversion errors and make the type conversion intent in your code clear.
• To convert one number type to another, use the current value to initialize a new number of the desired type, which is the type of the target.
• The conversion of integers and floating-point numbers must explicitly specify a type.

• 30.14159= Double (three) + Pointonefouronefivenine

• When a floating-point number is converted to an integer, floating-point values (fractional parts) are truncated.

Point 13.

Type aliases

code Example:

Typealias audiosample = UInt16          // the UInt16 type alias is defined as Audiosample // Maxamplitudefound is now 0  .  

Annotations:

• A type alias is one that defines another name for an existing type.
• Use the Typealias keyword to define the type alias.
• Once you have defined a type alias, you can use the alias anywhere you can use the original name.

Point 14.

Boolean value

code Example:

  True     // value is True false // value is False   

Annotations:

• Boolean values are logical true or FALSE.
• Swift has two Boolean constants, True and false.
• If a non-Boolean value is used where the Bool type is required, the type safety mechanism of Swift will error.

Point 15.

Meta-group

code Example:

the type of //  Http404error is (Int, String), the value is (404, "not Found")let Http404error = (404" Not Found ")  

Annotations:

• Tuples combine multiple values into a single composite value.
• The values within the tuple can be any type, do not require the same type, and the order of the types is arbitrary.
• The contents of a tuple can be decomposed into separate constants and variables, and then you can use them normally.

• Let (StatusCode, statusmessage) = http404error//  output "The status code is 404"println (" The status code is \ (statusCode)")//  output" The status message is not Found "println ("Thestatus message is \ (statusmessage)")

• If you only need a subset of the tuple values, you can use the underline (_) to mark the part you want to omit when decomposing.

• Let (Justthestatuscode, _) = Http404error//  output "The status code is 404"println ("  The status code is \ (justthestatuscode)")

• A single element in a tuple can be accessed by subscript, with the subscript starting from zero.

• // output "The status code is 404"println ("Thestatus code is \ (http404error.0)") // output "The status message is not Found"println ("Thestatus message is \ (Http404error.1)" /c11>)

• You can name a single element when you define a tuple, and you can get the value of an element by naming it.

•  $ " OK " )//  output "The status codeis a" println ("Thestatus code is \ ( Http200status.statuscode)//  output "The status message is OK"println ( " The status message is \ (http200status.description) ")

• Tuples can be used as return values for functions.

The Breeze to Touch Willow (Dashgeng)

Source: http://www.cnblogs.com/dashgeng/

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Wind notes-swift programming language: point11~15