go

golang

golangbot Hello World

package main

import "fmt"

func main () {
    fmt.Println("Hello World")
}

• Every go file starts with a package name statement. This forces you to write modular code.
• import "fmt" means to import the fmt package, short for formatted. The package allows the developer to use formatted i/o.
• func main is where the program begins. The main function always lives in the main package.
• fmt.Println writes texts to standard output (Stdout)

golangbot Variables

• syntax: var name type
• example: var name string
• %T prints the type
• int's default value is 0!

Type Inference

• if you initialize the value of your variable, you can skip the type declaration
  • For example: var name = "Kim" does not need the type "string"

Multiple Variables

• If they have the same type, you can separate variable names with a comma during the declaration
  • For example: var first_name, last_name string = "Kim", "Schlesinger"
• type inference works here, too

Short hand declaration

• :=
  • for example: name, age := "Kim", 34
  • no var
• Only works for newly declared variables

Types

(come back to this)

Functions

• golang syntax for functions:

func functionname(parametername type) returntype {
    \\ function body
}

• parameters and parametertypes are optional, so a function can look like this: func functionname(){}

Multiple Return Values

• a function that takes the length and width of a rectangle and returns the area and perimeter

package main

import "fmt"

func runCacluation(length, width float64)(float64, float64){
    var area = length * width
    var perimeter = (length + width) * 2 
    return area, perimeter 
}

func main(){
    area, perimeter ;= runCalcuation(10.8, 5.6)
    fmt.Printf("Area %f Perimeter %f", area, perimeter)
}

Named Return Values

func rectProps(length, width float64)(area, perimeter float64) {  
    area = length * width
    perimeter = (length + width) * 2
    return //no explicit return value
}

Blank Identifier

• _
• A way to discard a parameter you aren't using.

package main

import (  
    "fmt"
)

func rectProps(length, width float64) (float64, float64) {  
    var area = length * width
    var perimeter = (length + width) * 2
    return area, perimeter
}
func main() {  
    area, _ := rectProps(10.8, 5.6) // perimeter is discarded
    fmt.Printf("Area %f ", area)
}

Packages

• Write small, modular code with packages
• Every executable go app has a main function
  • the main function is the entry point for execution
  • the main function lives in the main package
• go install
• A good practice: package names match the directory they live in
• Capitalize function names in packages (Average instead of average)
• You can alias pacakge names in the import statement: import m "golang-book/chapter11/math

Conditional Statements

if condition {

} else if condition {

} else condition {

}``` 

or 

```go
if statement; condition {

}``` 

Example of the latter: 
```go
if name := "Kim"; name == "Kim" {
    fmt.Println("your name is", name)
} else {
    fmt. Println("I do not know your name")
}





## Misc. 

* `%s` is for string interpolation 
* `rune` is a 32-bit integer value
* `template` directory 
* a `struct` is a data structure that holds information that will be displayed in our HTML file 
* `http.FileServer(http.Dir("static"))`