IDL Types inheritance and casting into IDL

[SerafimArts]

I did not find answers to these questions in the spec: http://facebook.github.io/graphql/
In this I want to set some details.

The question concerns all types that allow the use of inheritance in the following cases:

1. type Object implements Interface {...}
2. type Object {...} extend Object {...}

Extending the number of arguments

# section-1
interface Interface {
    field: String
}

# section-2
type Object implements Interface {
    field(arg1: String): String
}

# section-3
extend type Object {
    field(arg2: String): String
}

1. Is it possible to expand the number of arguments during the interface implementation (section-2)? Or should there be an error?
2. Is it possible to expand the number of arguments during a type extension (section-3)? Or should there be an error?
   2.1) Extend complements field arguments? (The result looks like: field (arg1: String, arg2: String): String)
   2.2) Does the extension redefine the field arguments? (The result looks like: field (arg2: String): String)

It seems to me that the answers are the following (please correct):

1. Yes
2. Yes
   2.1) Yes
   2.2) No

Overriding of Container Types

The question concerns types NonNull and List.

# section-1
interface Interface {
    field(arg1: String): String
}

# section-2
type Object implements Interface {
    field(arg1: String!): String!
}

The table of allowed overrides ("container type-cast coercion") looks like this (correct, if I'm wrong):

Tags:

• :ok: - Allowed
• ❌ - Not allowed
• ? - I do not know

Definition	Implementation	Is acceptable?
Type	Type!	🆗
Type	[Type]	❌
Type	[Type!]	❌
Type	[Type]!	❌
Type	[Type!]!	❌
------------	----------------	----------------
Type!	Type	❌
Type!	[Type]	❌
Type!	[Type!]	❌
Type!	[Type]!	❌
Type!	[Type!]!	❌
------------	----------------	----------------
[Type]	Type	❌
[Type]	Type!	❌
[Type]	[Type!]	🆗
[Type]	[Type]!	🆗
[Type]	[Type!]!	🆗
------------	----------------	----------------
[Type!]	Type	❌
[Type!]	Type!	❌
[Type!]	[Type]	❌
[Type!]	[Type]!	❌
[Type!]	[Type!]!	🆗
------------	----------------	----------------
[Type]!	Type	❌
[Type]!	Type!	❌
[Type]!	[Type]	❌
[Type]!	[Type!]	❌
[Type]!	[Type!]!	🆗
------------	----------------	----------------
[Type!]!	Type	❌
[Type!]!	Type!	❌
[Type!]!	[Type]	❌
[Type!]!	[Type!]	❌
[Type!]!	[Type]!	❌

Overriding of Scalar Types

The question concerns the rules for converting scalar types during inheritance.

Example code:

# section-1
interface Interface {
    field: Int
}

# section-2
type Object implements Interface {
    field: Float
}

1. Are these type conversions permissible?
2. The table of allowed overrides ("scalar type-cast coercion") I can't imagine how it should look like :D

@leebyron I will be glad to receive help in answering these questions. Excuse me if I missed some nuances from the specification document =)))

[SerafimArts]

Thank you very much for helping emptiness =)))

Now you can safely implement LSP overriding, like:

interface UserInterface {
    id: String
}

interface UsersRepository {
    user: UserInterface
}

type User implements UserInterface {
    id: ID # String postcondition overridden by ID
}

type UserQuery implements UsersRepository {
    user: User! # Nullable Interface postcondition overridden by NonNull interface implementation
}