Types you define · 3 MIN READ

A struct is data, and its fields have names

Declare a struct type and build values of it without positional guessing.

A struct groups fields under a type name. Point{X: 1, Y: 2} names its fields; Point{1, 2} relies on declaration order. Reordering same-typed fields can silently change an unkeyed literal's meaning. Adding a field usually makes an existing unkeyed literal fail to compile. Keyed literals make intent clearer, and vet checks unkeyed literals for structs from other packages.

A struct's zero value is a struct, not nil. Each field begins at its own zero value. Fields beginning with an uppercase letter are exported; visibility is decided per field.

SEE THE IDEA

Field names make construction readable

01
Type
go
```
type Point struct { X, Y int }
```
A fixed set of fields
02
Keyed literal
go
```
Point{X: 3}
```
Omitted fields receive zero values
03
Copy
go
```
next := point
```
Copies the struct value

A struct value carries its fields together; assigning it copies that value.

In practice

Prefer keyed literals when the field meanings are not obvious. An omitted field is deliberately zero, which is helpful for configuration structs. A struct copy is shallow: slice, map and pointer fields still refer to the same backing data even though the outer struct is a new value.

Watch out

A copied struct containing a mutex must not be used as an independent lock after the original lock has been used.

Official reference ↗

Work through the exercise

package main

// Declare a Rect type with Width and Height fields of type int,
// then finish Area so it returns their product.

func Area(r Rect) int {
	return 0
}

func main() {
	println(Area(Rect{Width: 3, Height: 4}))
}

Try it yourself

Trace each value and write down your reasoning. Copy the source into GopherForge or your local Go environment to compile and check it. This web page does not execute your code or send it to a compiler service.

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