How do I create an arktype equivalent to Record<string, CustomInterface[]> with 2.0.0-beta.0?

[BinToss]

Context: I'm type-validating the JSON output of MSBuild project evaluation commands. One of the nested types in the JSON object is Record<string, IItemMetadata[]> where interface IItemMetadataWellKnown is MSBuild well-known item metadata & Record<string, string>.

I understand generics are W.I.P. and the tests for Record types are commented out. The solution, if there is one, will likely be esoteric.

import { type } from "arktype"

// I know Record types can be created with only builtin types...
const record_string_string = type("Record<string, string>");
const record_string_stringArray = type("Record<string, string[]>");
const record_string_objectArray = type("Record<string, object[]>");
const record_string_MapArray = type("Record<string, Map[]>");

// ...but Records with custom-typed values don't work—the custom type cannot be resolved.

const arrayItem = type({
  knownProp0: "string",
  knownProp1: "string"
}).and("Record<string, string>");
type ArrayItem = typeof arrayItem.infer

const arrayItemArray = type(arrayItem.array())
type ArrayItemArray = typeof arrayItemArray.infer

// Record<string, (typeof arrayItem.infer)[]

// Argument of type '"Record<string, typeof arrayItemArray.infer>"' is not assignable to parameter of type '"'typeof' is unresolvable "'. ts(2345)
const record0 = type("Record<string, typeof arrayItemArray.infer>")
// Argument of type '"Record<string, arrayItemArray>"' is not assignable to parameter of type '"'arrayItemArray' is unresolvable "'. ts(2345)
const record1 = type("Record<string, arrayItemArray>");
// Argument of type '"Record<string, ArrayItemArray>"' is not assignable to parameter of type '"'ArrayItemArray' is unresolvable "'. ts(2345)
const record2 = type("Record<string, ArrayItemArray>");
// Type 'Type<{ [x: string]: string; knownProp0: string; knownProp1: string; }[], {}>' is not assignable to type '"'$' is unresolvable "'. ts(2322)
const record3 = type({ "[$: string]": arrayItemArray })
// Argument of type '"{ [x:string]: arrayItemArray }"' is not assignable to parameter of type '"'{' is unresolvable "'. ts(2345)
const record4 = type("{ [x:string]: arrayItemArray }")

I've fiddled with Type<T0,T1>.constraint, pipe, and other methods that sound like they might help, but I couldn't figure out their intended usage even after referring to the unit tests.

[maurice]

Does this work for you?

import { type, scope } from "arktype";

////// with type

const iItemMetadata = type({ key1: "string", key2: "string" }, "&", { "[string]": "string" });

/*
type IItemMetadata = {
  [x: string]: string;
  key1: string;
  key2: string;
}
*/
type IItemMetadata = typeof iItemMetadata.infer;

const myRecord = type({ "[string]": iItemMetadata.array() });

/*
type MyRecord = {
  [x: string]: {
    [x: string]: string;
    key1: string;
    key2: string;
  }[];
}
*/
type MyRecord = typeof myRecord.infer;

////// or with scope

const types = scope({
	IItemMetadata: [
		{ key1: "string", key2: "string" },
		"&",
		{ "[string]": "string",	},
	],
	MyRecord: { "[string]": "IItemMetadata[]" },
}).export();

type IItemMetadata2 = typeof types.IItemMetadata.infer;
type MyRecord2 = typeof types.MyRecord.infer;

There may be a cleaner/more idiomatic way to do it though?

[ssalbdivad]

I would recommend @maurice's answer with the slight adjustment that you don't need an intersection to specify an index signature alongside literal keys:

const iItemMetadata = type({ key1: "string", key2: "string", "[string]": "string" });

const myRecord = type({ "[string]": iItemMetadata.array() });

Additionally, there will be an option to invoke builtin generics like Record directly on arbitrary definitions in the next release, so you will be able to use something like:

ark.Record("string", iItemMetadata)

Working on better docs for this now, sorry for the confusion in the meantime!

[nidomiro]

For anyone coming here in 2025, the syntax is nearly the same: type.Record("string", iItemMetadata)

[ssalbdivad]

ark is also available as an important containing all keywords.

Some of the most common like Record were attached to type as a convenience so that is definitely a convenient way to handle it in that case!

[nidomiro]

I just started using arktype, so I did not know that. Thanks for the Info👍