elm-review-no-primitive-type-alias

Provides elm-review rules to point out type aliases to simple primitive types (String, Char, Bool, Int, Float, ()).

Rationale

Type Aliases that point to simple primitive types can give a false sense of security because these type aliases provide a label that you could use in unintended ways without getting compiler feedback. For example, if you have two type definitions

type alias UserId = String
type alias ShippingAddress = String

Then you could miss out on helpful compiler feedback in the following scenarios:

Mistakenly use the type alias UserId on a value which actually represents a shipping address, or
Mistakenly use the type annotation String on a value which is actually a UserId
Mistakenly label a user ID value with the type ShippingAddress
Mix up positional arguments with types like ShippingAddress and UserId, but since they're just Strings as far as the compiler is concerned, there is no error to let you know.

All of these cases could provide you with more helpful compiler feedback if you use custom types like

type UserId = UserId String

and

type ShippingAddress = ShippingAddress String

instead.

See a more in-depth discussion in the Elm Radio episode about Primitive Obsession.

Provided rules

NoPrimitiveTypeAlias - Reports type aliases for simple primitive types.

Configuration

module ReviewConfig exposing (config)

import NoPrimitiveTypeAlias
import Review.Rule exposing (Rule)

config : List Rule
config =
    [ NoPrimitiveTypeAlias.rule
    ]

Try it out

You can try the example configuration above out by running the following command:

elm-review --template dillonkearns/elm-review-no-primitive-type-alias/preview

Modules

NoPrimitiveTypeAlias