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Chris Noring for Microsoft Azure

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Go from the beginning - Structs

Go from the beginning - Structs

Let's start with a simple scenario, you have an account balance. You might store it in a variable like so:

accountBalance int32
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Now that's great, but if you want to describe something more complex, like a bank account? A bank account consists of more information like that like id, balance, account owner and so on. You could try representing each one of those properties an integers like so:

var accountBalance int32
var owner string
var id int
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However, what happens if you need to operate on more than one bank account, I mean you could try to store it like so:

var accountBalance int32
var owner string
var id int

var accountBalance2 int32
var owner2 string
var id2 int
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It doesn't really scale though, what you need is a more complex type, like a struct that's able to group all this information like so:

type Account struct {
  accountBalance int32
  owner string
  id int
}
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Β References

https://www.golangprograms.com/go-language/struct.html

Defining a struct

Ok, so we understand why we need a struct, to gather related information, and we've seen one example so far Account. But let's try breaking the parts down and see how we go about defining a struct. Here's what the syntax looks like:

type <a name for the struct> struct {
  ... fields
}
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Let's show another example but this time we create a struct for an address:

type Address struct {
 city string
 street string
 postal string
}
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Create a struct instance

To create an instance from a struct, we can use one of two approaches:

  • define a variable, and set the fields after the variable declaration:
   var address Address
   address.city = "London"
   address.street = "Buckingham palace"
   address.postal = "SW1"
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  • define all at once, we can set all the values in one go as well:
   address2 := Address{"New York", "Central park", "111"}
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Embedding a struct

We can also embed a struct in another struct. Let's see we have our Address struct, an address is something that a higher level struct like Person can use. Here's how that can look:

type Person struct {
 name    string
 address Address
}
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In this code, the Person struct has a field address of type Address.

To instantiate this struct, we can type like so:

person := Person{
  name: "chris",
  address: Address{
   city: "Stockholm",
  },
 }
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Relying on default naming

Note how we created a field address, we can skip typing a few characters by defining it like so instead:

type Employee struct {
 Address
 company string
}
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Note how we omit the name for the field and just type Address, this means the field name and field type will be the same name. Creating an instance from it is very similar:

employee := Employee{
  Address: Address{
   city: "LA",
  },
  company: "Microsoft",
 }
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Adding implementation to structs

Structs are by its very nature just data fields that describes something complex. You can add behavior to it though by creating functions that operate on a struct. Here's an example:

func (a Address) string() string {
 return fmt.Sprintf("City: %s, Street: %s, Postal address: %s", a.city, a.street, a.postal)
}
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We've added a string() method. The method belongs to Address and we can see that with (...) right after the func keyword that takes a Address. The rest of the implementation returns a formatted string via Sprintf(). Given the following code:

var address Address
address.city = "London"
address.street = "Buckingham palace"
address.postal = "SW1"
fmt.Println(address.string())
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We would get the following output, when calling string():

City: London, Street: Buckingham palace, Postal address: SW1
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Summary

In this article, you've learned why you should group fields into a struct when you have many properties that describes something complex. Hopefully, you will use structs for these cases.

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