类型<名称> <数据类型>和类型<名称> = <数据类型>之间的区别是什么

Question

I'm new to Golang. I'm sorry but I'm still confused on what's the difference between:

type <Name> <dataType>

and

type <Name> = <dataType>

Here's an example:

package main

import "fmt"

func main() {
    var (
        strWord Word
        strText Text
    )
    strWord = "gopher"
    strText = "golang"

    fmt.Printf("strWord = %s, Type of Value = %T
", strWord, strWord)
    fmt.Printf("strText = %s, Type of Value = %T
", strText, strText)

}

type Word string

type Text = string

Output

strWord = gopher, Type of Value = main.Word
strText = golang, Type of Value = string

Then, when should we use between the two?

Answer 1

The first is a type declaration, the second is a type alias

Type declaration

Docs: https://golang.org/ref/spec#Type_declarations

This allows you to create a new distinct type <Name>, with the underlying type <datatype>.

You could define something like:

type Password string

And then reimplement the String() method for it so that it's never accidentally printed.

func (p Password) String() string {
    return "<redacted>"
}

Type alias

Type aliases are used mostly for iterative refactoring, where moving a type from one package to another would create too large a change / break too many things.

This article explains some usecases for it:

https://talks.golang.org/2016/refactor.article

But it essentially allows you to use one type as another.

package mypackage
type Foo struct {}


package other
type Bar = mypackage.Foo

You can now use other.Bar and mypackage.Foo interchangeably. They are the same type, with different names. Whereas type declaration is a new type.