When comparing Elm vs Unity, the Slant community recommends Elm for most people. In the question“What are the best game engines for web games?” Elm is ranked 1st while Unity is ranked 6th. The most important reason people chose Elm is:
Lack of run-time exceptions makes it easy to produce large swathes of reliable front-end code without drowning in tests.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro No run-time exceptions
Lack of run-time exceptions makes it easy to produce large swathes of reliable front-end code without drowning in tests.
Pro Inferred static typing
ML static typing is great because it's always there, you just choose how explicit you want to be and how much you want the compiler to do.
Pro Super easy refactoring with very helpful compiler errors
In no other language you can refactor so easy without any worries, since the compiler will guide you through. It is like TDD but than compiler-error driven.
Pro Designed around high-level front-end development
As Elm was designed as a front-end langauge, it has out of the box support for things like DOM-element creation, letting programmers focus on their application logic, rather than implementation details specific to the web.
Pro Great and simple way to learn Purely Functional Programming
You can try to apply some functional programming ideas in other languages that have an imperative basis, but you haven't seen the real power unless you tried it in the environment of purely functional programming. Elm is a simple language with great learning resources and easy graphical output, which makes it easy to explore the power of functional programming. Plus programming in Elm is very readable.
Pro Good tooling
All major editors have great support. With Atom for example, Elm plugins are available for linting, formatting, make/compiler support and Elmjutsu will simply overflow you with super useful functions, like navigate to referenced definition and show expression type.
Pro Batteries included
The Elm Architecture means you don't need to spend valuable time and effort choosing the right frameworks, state management libraries, or build tooling. It's all built in.
Pro Static module system
Elm uses easy to use modules.
Use:
import List
import List as L
import List exposing (..)
import List exposing ( map, foldl )
import Maybe exposing ( Maybe )
import Maybe exposing ( Maybe(..) )
import Maybe exposing ( Maybe(Just) )
Creation:
module MyModule exposing (foo, bar)
Pro Missing syntactic sugar
Easy to learn, most functions have only one way, not 5 alternatives where you must study where to best use what.
Pro Growing community
Pro Interactive Programming and Hot Swapping
Support for hot swapping and interactive programming is included.
Pro Easy to code review
The lack of side-effects and simple, consistent language semantics make it easy to quickly review incoming changes.
Pro Higher confidence in code correctness and quality
Pure functions, immutable data structures, amazing compiler, clean and homologous syntax used for HTML, logic, and optionally to replace CSS, elimination of entire classes of bugs so you don't even need most unit tests. These factors lead to better code, better programs, higher confidence, and ultimately, more satisfaction.
Pro Not quite Haskell semantics
Luckily you do not have to learn Haskell to be able to do any Elm. It is meant to be a language that compiles to Javascript, so for Javascript programmers (Front end) not for CS students who want to learn as many different algorithms as possible.
Pro Great community support
Unity is bolstered by a huge, helpful community via its official forums, wiki, Unity Answers, and Unity Asset Store; plus the most-subscribed subreddit of any game engine.
Pro OUYA support
Pro Over 20 platforms
Unity offers over 20 platforms for publishing including mobile, console, web, VR, and more.
Pro Versatile
Not tailored for specific types of games (like Unreal...), so it won't get in your way if you want to make something unique.
Pro Well structured
Overall, a coherent engine with a rational approach. People who complain a lot about being forced to hack around it usually do not read the docs, like the one that describes orders of execution, or specific functions hooks and such. Some like to say it lacks raw power where people who are used to standard optimizations have no problem. For example It is not uncommon to encounter users who complain about low FPS but forgot to activate occlusion, flag static elements, activate animations culling, and so on. As for complaints about C#, people who are transitioning from C++ were already bad at C++ before being bad at C#. They often come from the PC world where the sheer power of today's machines is very forgiving compared to the platforms we had to develop for in the 80s~90s. One of their errors is for example to never read this doc.
Pro Very optimized
Unity runs very smoothly even on systems that are considered "weak" by today's standards.
Pro Lots of assets can be found in the Asset Store
For those developers who can't afford an artist, or aren't skilled enough to create their own art, Unity features an Asset Store full of a wide variety of free and paid assets that can be easily added to a game. The Asset Store has more than just music and art. It also has code and modules that can be added to games including unique lighting or GUI systems. It also has powerful asset management and attribute inspection.
Pro Works with 3rd party IDEs
You can use any C# IDE for it, but the ones tested which have Unity integration are:
- Microsoft Visual Studio
- MonoDevelop
- Visual Studio Code (much faster than VS, but a bit harder to set up for Unity development)
- JetBrains Rider (very fast, has lots of functionality and best Unity integration, but it is not free)
Pro Flexibility is provided by a strong component programming model
Pro Has a great animation system
Unity provides a great state machine animation system called Mechanim allowing to separate animation from the model and assign the same animoations to different models.
Pro Powerful standard shaders
The built in standard shader in Unity 5 is incredibly optimized and supports PBS/PBR.
Pro Allows for rapid prototyping
Unity's modular system and usability allows for quickly developing a prototype of an idea. It has features like drag & drop editing, shaders, animation and other systems already in place to allow diving right into developing a game.
Pro Easy learning curve
The way the editor is structured, by setting scripts on objects, and the use of a high-level language, C#, makes it easy to learn.
Pro Can create custom forms and tools
Pro Very popular
Unity is a proven game engine. It is used by a wide range of developers - from small indies to triple-A companies such as Microsoft, Paradox, Square Enix and Sega.
Pro Lots of resources to learn from
Unity3D provides an exhaustive documentation where everything is given a full description supplied by a number of examples as well as video and text tutorials and live training sessions to understand the ins and outs of the engine. In addition there's an ever-growing community that can offer advice to help resolve any situations that may arise.
Along with the official Unity resources, there are many high quality (and often free) third party tutorials available.
Pro Great editor
The editor GUI is very powerful and intuitive. It allows pausing gameplay and manipulating the scene at any time as well as progress gameplay frame by frame. It also has powerful asset management and attribute inspection.
This allows it to be more powerful than other, simpler drag-and-drop engines such as Game Maker Studio, although it can take a bit more experience to learn the workflow.
Pro As of Unity 5 all engine features are free for everyone
As long as the company makes $100k or less, Unity's free version can be used to release games without purchasing the pro version.
Pro Supports 2D and 3D
With Unity knowledge of just one engine is needed to be able to create both 2D and 3D games.
Pro Great community
Great Community support through Forums and Unity Answers.
Pro Provides access to a huge list of assets through Asset Store
There's an Asset Store, providing free and paid assets (including components). It also has powerful asset management and attribute inspection.
Cons
Con Lack of typeclasses
Elm doesn't have typeclasses which means some code needs to be duplicated. A fix in a function that needs typeclasses means all of the duplicates need to be fixed too.
Con limited js interop
only one way ports are available as a crude js FFI. This means you can only call functions both directions but will not get a result.
Con Harder to get buy-in from devs and mgmt
It's a total divergence from what most people are used to in the JS ecosystem. The change in syntax can be scary, the change in approaching problems can be scary. The fact that it's not backed by FANG can be scary. The fact that it's not v1.0 can be scary. The governance model and the deliberately slow release cadence can be scary. There are a couple harsh medium articles, hackernews/reddit posts out there made by people with an ax to grind that can be scary if you don't have a better picture of the Elm community, the tradeoffs that have been made, or the benefits to be had over other options. None of these are good reasons to write off further investigation of a great tech, but it happens.
Con Code Repetition
Because of the lack of genericness Elm needs a lot of code to be repeated. There are 130+ implementations of map in elms core libraries.
Con Features get removed without warning
Often features that are deemed to be misused by the community like infix operators get removed without much of a warning.
Con Community harsh if criticised
If one even dares to start a discussion about a feature on elms slack, discord, subreddit or github one will be aggressively shut down often argueing that one should use purescript instead
Con Poor Windows support
Few if any of Elm's core contributors are Windows users and breaking bugs are sometimes left for weeks or months.
Con Good for beginners not good for experts
Development in elm is quite nice until you need some more advanced features. These however are actively discontinued and removed because elm wants to establish a "single way of doing things" philosophy
Con Updates break existing code often
The last few updates of elm broke existing code in major ways.
Con Adds an additional layer of abstraction
Some users claim that Elm adds an additional layer of abstraction, meaning that it is one more hurdle between the brain and the product.
Con Functional programming itself has quite a steep learning curve
Functional programming can be quite difficult to get your head around. It takes time to unlearn object orientational habits.
Con No Genericness in the future
Currently there is no code genericness like typeclasses possible, it has been officially stated that this will never change.
Con Not database-friendly
It is lots of work to make a server or database your "one source of truth", as Elm makes you write endless JSON parse boilerplate to talk to the server.
Con No Syntactic Sugar
Often you need to write longer and less readable code because there are no alternatives that are more concise.
Con No native editor for Linux
Though it builds for Linux, the Unity Editor runs only on Windows and Mac. Some users have successfully run the Windows version on Linux via Wine.