I am using io-ts to parse objects from JSON that can be any of a known variety of types. Each object comes in with a string key @type specifying what its type is. I would like to keep a Record/map of type names to io-ts type "class objects" so i can find the parsing class to use. This table needs to be the input to a function, and can be supplied by other libraries who consume this library. So I can't make assumptions about what sort of types are allowed, though I want to assume they will all have @type as a key.
but I am struggling to figure out how to specify what this table's type should be as a parameter. It seems to be something like "map of string to subclass of t.Type with at least the property @type." How would I specify that?
Example data:
[
{ "@type": "A",
"a": "hello"
},
{ "@type": "B",
"b": "world"
}
]
Code I am trying to write:
import * as t from 'io-ts';
export const A = t.type({
'@type': t.literal('A'),
a: t.string,
});
export const B = t.type({
'@type': t.literal('B'),
b: t.string,
});
// conceivably, any number of these may exist
export type TypesTable = Record<string, ???>
myParsingFunc(data: Data, table: TypesTable) {...}
One option I have been trying to get working is like this, but with the mystifying error showing up as commented:
export const SuperType = t.Type({
'@type': t.string
})
export type TypesTable = Record<string, T extends SuperType> // E: '?' expected
// Another option that produces an error, but doesn't even express the right thing, because i don't want every entry in the table to refer to the same type:
export type TypesTable<T extends SuperType> = Record<string, T> // E: SuperType refers to a value, but is used as a type here
Any guidance in interpreting this error or how to represent subclasses in type signatures like this would be super appreciated!
