Suppose I have the following code:
type User struct {
ID string
Username string
Name string
Password string
}
What I want to do is create another struct that can access certain fields from the User struct, instead of accessing all of it, to prevent people from seeing the password, for example. This does not work:
type Note struct {
ID string
Text string
UserID User.ID
}
Is there any way to do this, or do I simply create the Note.UserID field to have the same data type as the ID in the User struct?
Assuming the types are in different packages you can do this by exporting vs not exporting the fields. A field who's name begins with a lower case letter is not exported, meaning it is not visible outside the package where it is declared/defined. So, in this case if the user existed in one package, call it user while the other type were declared in another you could accomplish this 'hiding' of properties by changing the definition to;
type User struct {
ID string
username string
name string
password string
}
If the two types live in the same package there is no way of making a field private/hidden/ect, everything will be available in that scope.
The Go Programming Language Specification
An identifier may be exported to permit access to it from another package. An identifier is exported if both:
the first character of the identifier's name is a Unicode upper case letter (Unicode class "Lu"); and
the identifier is declared in the package block or it is a field name or method name.
All other identifiers are not exported.
Give User its own package and don't export the password.
For example,
package user
type User struct {
ID string
Username string
Name string
password string
}
func (u *User) IsPassword(password string) bool {
return password == u.password
}