Software Engineering

Numbers

Conversion between numbers can be done using a global built-in function with the type name.

myId := 10

myTicketPrice := 55.7



myIdAsFloat := float64(myId)
myTicketPriceAsInt := int(myTicketPrice)











Not every conversion is possible, e.g. a string into a bool.












Strings

Multiline strings can be created using backticks.

strSingle := "Just a single line of text."

strMulti := `We are
on multiple
lines here!`











Collections

What do we have?


Arrays

Fixed length

[5]int

Slices

Similar to dynamic length arrays, but are in practice chunks of arrays

[]int

Maps

Key-value dictionaries

map[keyType]valueType

// Example
map[string]int

Generics

Since Go version 1.18












TRY IT OUT

Rob Pike


  • Declare a new array with a length of 20 and type string.
  • Declare a new slice with the type int.
  • Declare a new map with a key of type int and a value of type string.
  • Discuss the special function init. This is not the same as main() ! Not a constructor.
  • The len() function returns the length of a collection.











Collections are not objects. We use global functions to work with collections, such as len() and cap().












Arrays and slices

Remember, arrays are fixed length and slices are dynamic length.


Arrays

var countries [180]string
countries[0] = "Denmark"

// Initialize with values, shorthand notation
accounts := [5]int{1, 2, 3, 4, 5}

Slices

Declaring a string slice.

We use append to add values and note that the new slice is assigned back to the variable.

var countries []string
countries = append(countries, "Denmark")

Initialize with values.

Overrides any capacity defined in the declaration.

var countries = []string{"Denmark", "Sweden", "Norway"}
println(len(countries))

Initialize with a capacity of 5.

This defines the default increment size when the slice runs out of space.

var countries = make([]string, 5)











Maps

Pay attention to the type definition.

  • For maps the default value is nil—initialization is required.

var platformUsers = map[string]int{"Facebook": 1000000, "Twitter": 500000}











The make() function can also be used to initialize a map and this is most commonly what is done as maps are rarely small in size.

var platformUsers = make(map[string]int)

platformUsers["Facebook"] = 1000000
platformUsers["Twitter"] = 500000