GenericDict

A wrapper over Dict from elm/core that allows you to use any types as keys.

Unlike existing solutions, doesn't store functions in the data structure and doesn't have any performance implications (except slightly higher memory usage because it stores both original keys and their stringified versions), but requires you to explicitly pass a key -> String function that tells how to convert your key type to a String to all functions that need it.

Other differences from elm/core

The standard Dict sorts key-value pairs in the order of keys. In this library key-value pairs are sorted by stringified versions of keys. But with non-comparable types that are just converted to String, thinking about the order doesn't make that much sense. So the idea is that you should consider the order an implementation detail and shouldn't rely on it when using functions like keys and values. And because of this, instead of having foldl and foldr, this library exposes only one function, which is named fold.

Example

module User exposing (Id, User, new, idFromString, idToString)


-- In reality I would use custom types for `name`, `email`, and `age`.
-- And I would also add checks for `Id` format!


type Id
    = Id String


type User
    = User
        { name : String
        , email : String
        , age : Int
        }


new : 
    { name : String
    , email : String
    , age : Int
    }
    -> User
new =
    User


idFromString : String -> Id
idFromString =
    Id


idToString : Id -> String
idToString (Id string) =
    string

module Data exposing (users)

import User exposing (User)
import GenericDict as Dict exposing (Dict)


users : Dict User.Id User
users =
    Dict.fromList User.idToString
        [ ( User.idFromString "ef5f03aa-30d8-41fa-9730-9074daffbfd2" 
          , User.new
              { name = "Bob"
              , email = "[email protected]"
              , age = 25
              }
          )
        , ( User.idFromString "b6c87ad8-d8b8-4f91-a680-6fec7c1aefb6" 
          , User.new
              { name = "Alice"
              , email = "[email protected]"
              , age = 22
              }
          )
        , ( User.idFromString "3a84502a-2423-4168-9f5e-1b5fe8eff034" 
          , User.new
              { name = "Chuck"
              , email = "[email protected]"
              , age = 30
              }
          )
        ]

-- Get a user
Dict.get User.idToString id Data.users

-- Add a new user
Dict.insert
    User.idToString
    id
    (User.new { name = "Eve", email = "[email protected]", age = 26 })
    Data.users

-- Remove a user
Dict.remove User.idToString id Data.users