gopherlabs.collabnix.com - Types - slice, map, new, make, struct in Golang

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Types - slice, map, new, make, struct

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3. https://golang.org/ref/spec

4. ● slice
https://play.golang.org/p/pYxENZqmCOU

6. https://play.golang.org/p/9U46JgUx9zW
0 - a
1 - b
2 - c
3 - g
4 - m
5 - z

7. ● making a Slice
https://play.golang.org/p/ZZVKKlFpSpC
0 Kannada - Shubhodava
1 Konkani - Dev Tuka Boro Dis Divum
2 Korean - Annyunghaseyo
3 Latvian - Labrit
4 Lithuanian – Labas Rytas
5 Macedonian - Dobro utro
6 Malayalam – Namaskaram
7 Maltese – L-Ghodwa t-Tajba
8 Mandarin – Nin hao
9 Marathi - Suprabhat
Kannada - Shubhodava
Konkani - Dev Tuka Boro Dis Divum
Korean - Annyunghaseyo
Latvian – Labrit
Lithuanian – Labas Rytas
Macedonian - Dobro utro
Malayalam – Namaskaram
Maltese – L-Ghodwa t-Tajba
Mandarin – Nin hao
Marathi - Suprabhat

8. ● Slicing a Slices
https://play.golang.org/p/IKvj069CHzv

9. ● making a slice
https://play.golang.org/p/r21LWwwQ9y-
If we think that our slice might grow, we can set a capacity larger than
length. This gives our slice room to grow without golang having to create
a new underlying array every time our slice grows. When the slice
exceeds capacity, then a new underlying array will be created. These arrays
double in size each time they’re created (2, 4, 8, 16) up to a certain point,
and then they scale in some smaller proportion.

10. ● appending to slice
https://play.golang.org/p/dSDiSBTiJC7

11. ● appending beyond capacity to a slice
https://play.golang.org/p/jJdMcszsJRM
If we think that our slice might grow, we can set a capacity larger than
length. This gives our slice room to grow without golang having to
create a new underlying array every time our slice grows. When the
slice exceeds capacity, then a new underlying array will be created.
These arrays typically double in size each time they’re created (2, 4, 8,
16).

12. ● appending slice to a slice
notice the syntax
args...
https://play.golang.org/p/6OIh7zeM5Nj

13. ● delete from Slice
https://play.golang.org/p/Z7H6GdPgDMy

14. ● exercise
● write a program that creates a slice of ints
using shorthand notation then prints the slice
● write a program that creates a slice of strings
using shorthand notation then prints the slice
● create a slice of ints using make;set the length
to 5 and capacity to 10
● append a slice to a slice
● delete an element from a slice.

15. ● Map [key , value]

16. ● map
● basic info
○ key:value
○ maps keys to values
○ called “dictionaries” in some languages
○ built into the language (not an additional library
you must import) so they’re first-class citizens
● Map Keys
○ need to be unique
○ the type used for a key needs to have the
equality operator defined for it
■ the type must allow equals comparisons
■ can’t use these types
● slice
● map
● Maps are Reference Types
○ they behave like pointers
○ when you pass a map variable to a function
■ any changes to that mapped variable
in the function
■ change that original mapped variable
outside the function
● Maps are Not Thread Safe
○ best to avoid using maps concurrently

17. ● Shorthand for Creating Map
https://play.golang.org/p/ptO8KjvdKNt

18. ● adding an entry to a map
https://play.golang.org/p/Tia8HLGK3mD https://play.golang.org/p/0dZnCo440k7

19. ● updating /delete an entry
https://play.golang.org/p/LbZJt2y8UFn https://play.golang.org/p/MAXxKaxgfnw

20. ● comma-ok-idiom
check for existence
comma ok idiom

21. ● comma-ok-idiom
check for existence
comma ok idiom
https://play.golang.org/p/f9LMgiobYMm

22. ● range loop
https://play.golang.org/p/K0G_Etz_uVo

23. ● make a map
https://play.golang.org/p/fTAwe3wEWoL

24. ● exercise
create a program that:
● creates a map using shorthand notation
● adds an entry to the map
● changes an entry in the map
● deletes an entry in the map
● prints all of the entries in the map using range
● prints the len of the map
● uses the comma ok idiom

25. ● make vs new
● make
○ slices, maps, channels
○ allocates memory
○ initializes
■ puts 0 or empty string into values
● new
○ returns a pointer
■ newly allocated
■ zeroed value
● “returns a pointer to a
newly allocated zeroed
value of type T”
https://play.golang.org/p/ij1aXv6J7HE

26. ● new
○ returns a pointer
■ newly allocated
■ zeroed value
● “returns a pointer to a newly allocated
zeroed value of type T”
make vs new
● make
○ slices, maps, channels
○ allocates memory
○ initializes
■ puts 0 or empty string into values
https://play.golang.org/p/rKcc3Lv8bOY

27. ● zero value
false for booleans, 0 for integers, 0.0 for floats, "" for strings
nil for pointers, functions, interfaces, slices, channels, and maps

28. ● make vs new
● new
○ returns a pointer
■ newly allocated
■ zeroed value
● “returns a pointer to a newly
allocated zeroed value of type T”
● make
○ slices, maps, channels
○ allocates memory
○ initializes
■ puts 0 or empty string into values
https://play.golang.org/p/hYm8y3AiQDV

29. ● make vs new
● make
○ slices, maps, channels
○ allocates memory
○ initializes
■ puts 0 or empty string into values
● new
○ returns a pointer
■ newly allocated
■ zeroed value
● “returns a pointer to a newly
allocated zeroed value of type T”
https://play.golang.org/p/zXpIGWTFP5A

30. ● make vs new
● make
○ slices, maps, channels
○ allocates memory
○ initializes
■ puts 0 or empty string into values
https://play.golang.org/p/r77ksucKjSi
● new
○ returns a pointer
■ newly allocated
■ zeroed value
● “returns a pointer to a newly
allocated zeroed value of type T”

31. ● make
○ slices, maps, channels
○ allocates memory
● initializes
■ puts 0 or empty string into values
● make vs new
https://play.golang.org/p/lhOc5lXQizU

32. ● make vs new
● make
○ slices, maps, channels
○ allocates memory
● initializes
■ puts 0 or empty string into values
https://play.golang.org/p/RRyqZc8q0oI

33. ● make vs new
● make
○ slices, maps, channels
○ allocates memory
● initializes
■ puts 0 or empty string into values
https://play.golang.org/p/Z64HscwjFc_L

34. ● make vs new
● make
○ slices, maps, channels
○ allocates memory
● initializes
■ puts 0 or empty string into values
https://play.golang.org/p/qI1mMyumewG

37. ● exercise
create a program that:
● declares a variable of type int using new
○ (note: this is not idiomatic go code to create an int this way)
● print out the memory address of the variable
● print out the value of the variable
● true or false:
○ new returned a pointer
create a program that:
● declares a variable of type string using new
○ (note: this is not idiomatic go code to create an string this way)
● print out the memory address of the variable
● print out the value of the variable
● true or false:
○ new returned a pointer

38. ● exercise
create a program that:
● declares a variable of type bool using new
○ (note: this is not idiomatic go code to create an bool this way)
● print out the memory address of the variable
● print out the value of the variable
● true or false:
○ new returned a pointer

39. ● exercise
create a program that:
● declares a variable of type[]int using make
● print out the value of the variable
● true or false:
○ make returned a pointer
create a program that:
● declares a variable of type map[int]string using make
● print out the value of the variable
● true or false:
○ make returned a pointer

40. ● What are the zeroed values for int, string,
bool?
● What are the zeroed values for slice and map
● Explain the difference between make and
new

41. ● struct – grouped fields
create a struct
and initialize it
https://play.golang.org/p/UJ1xEwy4VOP

42. accessing fields using
dot notation
https://play.golang.org/p/rb1oslM6Y3r

43. accessing fields using
dot notation

44. initialize a variable
naming the fields
https://play.golang.org/p/sV4dqi5UJI-

45. initialize a variable
omitting fields
https://play.golang.org/p/I4hJzlyQurZ

46. viewing the type
of p1
We have created our own type
which is interesting to think about!
https://play.golang.org/p/FiT64-Cel9_m

47. taking the address of a struct
p1 is of type *person
https://play.golang.org/p/tSM8aNvoO4n

48. ● new
○ returns a pointer
■ newly allocated
■ zeroed value
● “returns a pointer to a newly allocated zeroed
value of type T”

49. ● question
Can we use make with a struct?

50. question
Can we use make with a struct?
no
make is for slices, maps, and channels
● make
○ slices, maps, channels
○ allocates memory
● initializes
■ puts 0 or empty string into values

51. https://play.golang.org/p/ysOO98tL_3t

52. https://play.golang.org/p/OBlHXTz3pEO

54. ● exercise
create a program that:
● defines a struct type to hold customer info
● initialize two variables using that struct type
● uses dot-notation to print a field from each of
the variables
● changes the value of one of the fields
● prints the changed field
● Can you use new to create a variable of a
struct type?

55. ● question
Can you use make to create a variable of a struct type?

56. ● Review
● slice vs. slicing vs. index access
● slice
○ list
○ mySlice := []int{1, 3, 5, 7, 9, 11}
○ greeting := make([]string, 3, 5)
○ greeting = append(greeting, "Hello")
○ mySlice = append(mySlice, myOtherSlice...)
○ mySlice = append(mySlice[:2], mySlice[3:]...)
● map
○ key, value
■ key type, element type
○ initializing
■ myMap := map[int]string{<entries>}
■ otras := make(map[string]string)
○ adding new entry
■ otras[“new key”] = “new value”
○ changing entry
■ otras[“new key”] = “newer value”
○ delete entry
■ delete(otras, “new key”)
● comma ok idiom
○ if val, ok := myGreeting[2]; ok {
fmt.Println("val: ", val)
fmt.Println("exists: ", exists)
}
● make
○ slices, maps, channels
○ allocates memory
● initializes
■ puts 0 or empty string into values
● new
○ returns a pointer
■ newly allocated
■ zeroed value
● “returns a pointer to a newly
allocated zeroed value of
type T”
● struct
○ grouped fields
○ type person struct { name string age int
}
○ p1 := person{name: "James"}

57. ● References
● https://gopherlabs.collabnix.com
● https://godoc.org/
● https://golang.org/doc/

58. Thanks!
Any questions?
@sangambiradar@BiradarSangamSangam Biradar