Implicit cast of string vs. []byte

[Ivan Bertona]

Hello,

When I try to compile this piece of code:

package main

type MyString string

type MyBytes []byte

func GetString() (string, error) {

return "", nil

}

func GetBytes() ([]byte, error) {

return nil, nil

}

func main() {

var s MyString

var b MyBytes

var err error

s, err = GetString()

b, err = GetBytes()

}

I get this error: tmp/sandbox008752331/main.go:19: cannot assign string to s (type MyString) in multiple assignment 

Does anyone know why implicit casting from []byte to MyBytes works, but it doesn't for string to MyString?

Best,

Ivan

[Ayan George]

On 06/24/2017 08:16 PM, Ivan Bertona wrote:
> Hello,
>
> When I try to compile this piece of code:
>

I think it violates the second assignability rule since both 'string'
and MyString are named types. string happens to be a a pre-declared
named type:

https://golang.org/ref/spec#Assignability

Whereas []byte is unnamed therefore at least one of the types in the
expression is unnamed.

Here are a couple of relevant blog posts about it:

https://medium.com/learning-the-go-programming-language
http://www.laktek.com/2012/01/27/learning-go-types/

Someone please correct me if I'm wrong.

-ayan

[Ivan Bertona]

I see, thank you!

[Stefan Nilsson]

This may not be what you want, but starting from Go 1.9 it's possible to declare a type alias using the syntax

type MyString = string

As opposed to a type definition, an alias declaration doesn't create a new distinct type different from the type it's created from. Type aliases are not meant to be an everyday feature of Go, but are intended to be used during large and complex code refactoring.