Allow overrides to be used for unknown types

[danieljharvey]

Hi! Hope you're well. I'm trying to work out a way of generating arbitraries for stuff like the date codec from io-ts-types, and came up with this. Is this something you'd consider?

Thanks
Dan

[giogonzo]

Hi @danieljharvey! In fact, support for custom codec was there in the first version, I removed it here because it is inherently unsafe unless we take extreme care in defining a proper signature.

I'm not OK with throwing, but we could define two overloads as follows:

export function getArbitrary<T extends HasArbitrary>(codec: T): fc.Arbitrary<t.TypeOf<T>> {
export function getArbitrary<T extends HasArbitrary>(codec: T, overrides: Overrides): Option<fc.Arbitrary<t.TypeOf<T>>>

and return none if nothing matched.

Also the "matching" part is looks a bit brittle as defined in your PR here (i.e. not all custom codecs will have a name property). I would prefer something along the lines of:

type Overrides = Array<(input: unknown???) => Option<Arbitrary<unknown>>>

[danieljharvey]

Hey! Thanks for taking a look - all sounds very sensible - will have a poke around with some of the other custom io-ts-types and see if I can come up with something that fits them all.

[danieljharvey]

Closing in favour of #4