Declaring a variable in Go
Use the var keyword followed by the identifier followed by the type.
var varName type
var num int
Declaring and initializing a variable in Go
var varName type = value
var name string = ‘Joseph’
Shorthand for declaring and initializing a variable in Go
Go figures our what type the variable is even though it does not specify a type.
varName := value
name := ‘Joseph’
Declaring multiple variables at once
var var1, var2, var3 type
var num1, num2, num3 int
Declaring multiple variables at once and initializing values
var var1, var2, var3 type = value1, value2, value 3
Shorthand for declaring multiple variables at once and initializing values
You can use the colon equals operator to declare and initialize the variable.
var1, var2, var3 := val1, val2, val3
Grouping declaration and initialization
Go will figure out the type if one is not specified.
a int = 0 // integer
b = 1.618 + 6i // complex number
c = 3.1415 // floating-point number
Use the const keyword before the identifier. Once a constant is declared, its value cannot be changed.
const num1 float64 = 3.14157
Built-in types with Go
Booleans are used to represent the truth of something, so they can hold a value of true or false. Also, the zero value of a boolean type is false.
var y bool // y has a zero value of false
var x bool = true // x has a value of true
- Integers - int and uint will have a bit size of the computer running Go.
- int, int8, int16, int32, int64
- uint, uint8, uint32, uint64
- Floating-point numbers
- float32, float64
- Complex numbers
- complex64, complex128
A string is a sequence of letters or characters.
var name string = “Joseph” // name = “Joseph”
The zero value of the string type is an empty string (“”)
var color string // color = “”
Strings follow zero-based numbering and are represented in UTF-8 format.
Character J o s e p h
Index 0 1 2 3 4 5
Iota constant generator
Go's iota identifier is used in const declarations to simplify definitions of incrementing numbers. Because it can be used in expressions, it provides a generality beyond that of simple enumerations.
The values of iota is reset to 0 whenever the reserved word const appears in the source (i.e. each const block) and increments by one after each ConstSpec e.g. each Line. This can be combined with the constant shorthand (leaving out everything after the constant name) to very concisely define related constants.
- Iota: http://golang.org/doc/go_spec.html#Iota
- Constant declarations: http://golang.org/doc/go_spec.html#Constant_declarations
The keyword “import” is used for importing a package into other packages.
The package “fmt” comes from the Go standard library. When you import packages, the Go compiler will look on the locations specified by the environment variable GOROOT and GOPATH. Packages from the standard library are available in the GOROOT location. The packages that are created by yourself, and third-party packages which you have imported, are available in the GOPATH location.
Import statements can be grouped
Installing third-party packages
Download and install third-party Go packages by using “Go get” command. The Go get command will fetch the packages from the source repository and put the packages on the GOPATH location.
go get github.com/aeiou/json