In Polkadot Apps developer tab how do you encode a Rust tuple?

Question

There are several examples for including custom Rust types declared in a runtime module that can be applied Polkadot Apps interface here. However I am not sure how to encode tuples. This would also be the case for anyone else planning on using Tuples in their code and runtime API for use in polkadot-js.

Here's how it is declared in a Substrate Runtime module:

// tuple (struct)
pub type Code = u16;
pub type Type = u16;
pub struct Tuple(Code, Type);

// Complex struct using tuple
pub struct Record<T::AccountId,Tuple> {
    pub address: T::AccountId,
    pub tuple_values: Tuple,
}

// Storage
Record get(record):
        map T::AccountId => Option<Record<T::AccountId,Tuple>>;

I am presuming I would add something like this to the Developer tab in the Polkadot Apps settings, but I don't know if this is the correct syntax to use.

{
    "Code": "u16",
    "Type": "u16",
    "Tuple": ["Code", "Type"],
    "Record": {
        "address": "AccountId",
        "tuple_values": "Tuple"
    }
}

score 4 · Accepted Answer · edited Feb 27 '22 at 12:08

Tuples, Tuple structs, and Named structs are all encoded the same way. From https://docs.substrate.io/v3/advanced/scale-codec#tuples :

Tuples A fixed-size series of values, each with a possibly different but predetermined and fixed type. This is simply the concatenation of each encoded value.
…
For structures, the values are named, but that is irrelevant for the encoding (names are ignored - only order matters).

So in your case something like this will work:

{
    "Code": "u16",
    "Type": "u16",
    "Tuple": {
        "bogus_name_1": "Code",
        "bogus_name_2": "Type"
    },
    "Record": {
        "address": "AccountId",
        "tuple_values": "Tuple"
    }
}

In Polkadot Apps developer tab how do you encode a Rust tuple?

1 Answers1