V: Option type default value

[andrewda]

Take the example given in the documentation:

struct User {
    id int 
} 

struct Repo {
    users []User 
} 

fn new_repo() Repo {
        user := User{id:10}
        return Repo {
                users: [user]
        }
} 

fn (r Repo) find_user_by_id(id int) User? { 
    for user in r.users {
        if user.id == id {
            // V automatically wraps this into an option type  
            return user 
        } 
    } 
    return error('User $id not found') 
} 

fn main() {
    repo := new_repo() 
    user := repo.find_user_by_id(10) or { // Option types must be handled by `or` blocks  
        return  // `or` block must end with `return`, `break`, or `continue`  
    } 
    println(user.id) // ==> "10"  
} 

This will simply terminate the program if the user is not found. What if I instead wanted to specify a default value to use in this case? Kotlin handles this very elegantly, in my opinion, with the Elvis operator:

fn main() {
    repo := new_repo() 
    user := repo.find_user_by_id(99999) ?: User{id: 5}
    println(user.id) // ==> "5"  
}

Another way I could see implementing this is through the or block:

fn main() {
    repo := new_repo() 
    user := repo.find_user_by_id(99999) or {
        User{id: 5}
    }
    println(user.id) // ==> "5"  
}

I think something like this might be a very valuable addition.

[medvednikov]

Yes, I thought about this. Most likely the second option will be implemented:

user := repo.find_user_by_id(99999) or {
        User{id: 5}
}

[ntrel]

As the block just contains an expression, not statement(s), why not make or an expression instead:

user := repo.find_user_by_id(99999) or User{id: 5}

[ntrel]

As the block just contains an expression, not statement(s)

Alex explained for if expressions that the block can contain statements too, so I think or {st; value} is best for consistency.

[medvednikov]

This has been implemented: x := opt() or { 10 }