Dicts with any type as a key and Sets with any type as a member

elm-package install edkelly303/elm-any-type-collections 1.0.0


Any-type collections

This package allows you to use any custom types, records and other non-comparable types as keys for a Dict or members for a Set.

Quick example

type Id = 
    Id Int

dict = 
        { fromComparable = Id
        , toComparable = \(Id int) -> int

myFirstDict = 
        [ (Id 1, "foo")
        , (Id 2, "bar")

anotherDict =
    dict.insert (Id 3) "baz" myFirstDict

See "How to use this package" for a more detailed walkthrough.

Differences from elm/core's Dict and Set

1. Type signature

The Dict and Set types in this package each have an additional type parameter, which represents the comparable type used to store the key/member under the hood.

  • Instead of Dict comparable value, we have Dict key value comparable
  • Instead of Set comparable, we have Set member comparable.

2. Use of Interface types

We do not use top-level functions like Dict.get or Set.insert to interact with the Dict and Set types from this package.

Instead, we create Interfaces for each type. An Interface is simply a record containing functions that mirror the API of elm/core's Dict and Set implementations.

Why would you use this package?

  • Its Dict and Set data structures do not contain any functions, which means you can use them in Model and Msg types without any caveats. This is a different approach from several other packages, including:

  • turboMaCk/any-dict

  • jjant/elm-dict

  • owanturist/elm-avl-dict

  • timo-weike/generic-collections in its AutoDict and AutoSet modules

  • It offers similar performance characteristics to the elm/core Dict and Set implementations. Each function has the same Big-O complexity as its elm-core equivalent. By contrast:

  • pzp1997/assoc-list has similar performance characteristics to a List, which is no problem for small dictionaries but may get slower with larger ones.

  • jjant/elm-dict takes an interesting approach, which may make it faster in some circumstances and slower in others - check its README for more details.

  • See the "Performance" section for benchmarks.

  • Depending on your preferences, it may feel more ergonomic than packages whose API requires conversion functions to be passed in as an argument each time you call a Dict/Set function, such as:

  • truqu/elm-dictset

  • timo-weike/generic-collections in its ManualDict and ManualSet modules

Why wouldn't you use this package?

  • It requires the user to define an Interface type for each type of Dict or Set, as well as functions to convert the key/member type to and from a comparable type - so there is a certain amount of boilerplate involved.

  • It may just feel too weird to call dict.get instead of Dict.get. This type of API, based on a record-of-functions, is not common in Elm packages, and may make the code harder to understand for people who are not familiar with it.

  • It may increase asset size, since the final bundle of compiled code will include all the functions from elm-core Dict and/or Set, even if your code doesn't use them all. See the "Asset size" section for more details.

How to use this package

A common use case is when you have a wrapper type, such as an Id:

-- module Id exposing (Id, fromInt)

type Id
    = Id Int

toInt : Id -> Int
toInt (Id int) = 

fromInt : Int -> Id
fromInt int = 
    Id int

You cannot use an Id as a key for an elm-core Dict, because Id is a custom type, and custom types are not comparable.

However, with the Dict implementation from this package, you can get around the problem. You just have to create an Interface by supplying two functions:

  • A function to turn your Id type into a comparable
  • A function to turn that comparable type back into an Id

Let's define the Interface as a top-level value inside our Id module. We'll call it dict, and expose it from the module:

-- module Id exposing (Id, dict, fromInt)

import Any.Dict

dict = 
        { fromComparable = fromInt 
        , toComparable = toInt

Now, we can use this Interface to create and work with Id-keyed Dicts anywhere in our code:

-- module SomeOtherModule exposing (..)

import Any.Dict exposing (Dict)
import Id exposing (Id)

myFirstDict : Dict Id String Int
myFirstDict = 
        [ (Id.fromInt 1, "foo")
        , (Id.fromInt 2, "bar")

anotherDict : Dict Id String Int
anotherDict =
    Id.dict.insert (Id.fromInt 3) "baz" myFirstDict


The benchmarks folder contains some basic benchmarks comparing some of the commonly used Dict functions in this package to their equivalents in other similar Elm packages.

Without going into too much detail, this package offers broadly similar performance characteristics to elm-core Dict. It is slightly slower in all cases due to the need to convert between the user's key type and the comparable type used to represent it internally.

Side note: jjant/elm-dict seems crazy fast for a lot of these operations! So if you don't need to worry about the fact that its data structure contains functions, it might be worth checking out.

See the README in the benchmarks folder for instructions on how to run the benchmarks.

Asset size

The asset-size folder contains a script that allows you to compare the size of the JavaScript output from this package against the output of an equivalent elm-core program.

On my machine, the results are as follows:

>> Compiled size
Any.js:         121261 bytes
Core.js:        91544 bytes

>> Minified size
Any.min.js:     15144 bytes
Core.min.js:    7057 bytes

>> Gzipped size
Any.min.js.gz:  5241 bytes
Core.min.js.gz: 2927 bytes

See the README in the asset-size folder for instructions on how to run the script.