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I talked about the XML and JSON serialization of F# types in a previous post, and since then F# 3.0 has been released and a new [CLIMutable] was quietly added amidst the hype surrounding the awesome type providers!
When applied to a F# record type, the CLIMutable attribute tells the F# compiler to generate a default parameterless constructor as well as property getters and setters so that when working with the record type from other .Net languages it’ll appear as a pretty standard, mutable CLI type that you’d expect.
However, when working in F#, the normal rules as far as record types are concerned still apply – immutability by default, pattern matching, cloning using the with keyword, etc.
For a simple record type Person, let’s have a look at the compile code with and without the CLIMutable attribute:
Without the CLIMutable attribute, this is how the record type is normally compiled:
With the CLIMutable attribute applied, things look a lot different:
That’s all well and good, but why is this useful you might ask?
Because many serializers, such as the BCL’s XmlSerializer (as well as other serializers available in the open source space) only work with types that has a default constructor and contains property setters.
XmlSerializer and Record types
Unlike the DataContractSerializer which only requires a type to be decorated with a Serializable or DataContract attribute, the XmlSerializer on the other hand, also requires the type to define a parameterless constructor.
Whilst both serializers generate XML outputs, DataContractSerializer is intended for marshalling data (that conforms to a ‘contract’) for transportation over the wire and therefore less concerned with readability of its output and offers little option for you to customize the generated XML. It’s therefore quite happy to spit out rather unreadable XML for our Person record type above:
Meanwhile, in the land of the XmlSerializer, its sole purpose of existence is to generate XML and offers a platoon of options to help ensure its output meets your functional and aesthetic needs. By default it’ll generate nice, indented output for our CLIMutable version of Person record type:
In addition, you can customize the XML output using the normal XML-related attributes:
Of the OSS JSON serializers I benchmark regularly, JSON.Net (v4.5.11 tested) works with both normal and CLIMutable record types from F#. ServiceStack.Text (v3.9.37 tested) doesn’t work with ‘vanilla’ record types on deserialization (fields are left with default values), but you can workaround by making the fields mutable or add the CLIMutable attribute to the type.
I hope this proves to be useful to you, and if like us you have a lot of C# code hanging around just to get pretty XML out of your F# record types, dare I say it’s about to throw away those C# code!
Hi, I’m Yan. I’m an AWS Serverless Hero and I help companies go faster for less by adopting serverless technologies successfully.
Are you struggling with serverless or need guidance on best practices? Do you want someone to review your architecture and help you avoid costly mistakes down the line? Whatever the case, I’m here to help.
Skill up your serverless game with this hands-on workshop.
My 4-week Production-Ready Serverless online workshop is back!
This course takes you through building a production-ready serverless web application from testing, deployment, security, all the way through to observability. The motivation for this course is to give you hands-on experience building something with serverless technologies while giving you a broader view of the challenges you will face as the architecture matures and expands.
We will start at the basics and give you a firm introduction to Lambda and all the relevant concepts and service features (including the latest announcements in 2020). And then gradually ramping up and cover a wide array of topics such as API security, testing strategies, CI/CD, secret management, and operational best practices for monitoring and troubleshooting.
If you enrol now you can also get 15% OFF with the promo code “yanprs15”.
Check out my new podcast Real-World Serverless where I talk with engineers who are building amazing things with serverless technologies and discuss the real-world use cases and challenges they face. If you’re interested in what people are actually doing with serverless and what it’s really like to be working with serverless day-to-day, then this is the podcast for you.
Check out my new course, Learn you some Lambda best practice for great good! In this course, you will learn best practices for working with AWS Lambda in terms of performance, cost, security, scalability, resilience and observability. We will also cover latest features from re:Invent 2019 such as Provisioned Concurrency and Lambda Destinations. Enrol now and start learning!
Check out my video course, Complete Guide to AWS Step Functions. In this course, we’ll cover everything you need to know to use AWS Step Functions service effectively. There is something for everyone from beginners to more advanced users looking for design patterns and best practices. Enrol now and start learning!
Here is a complete list of all my posts on serverless and AWS Lambda. In the meantime, here are a few of my most popular blog posts.
- All you need to know about caching for serverless applications
- Lambda optimization tip – enable HTTP keep-alive
- You are wrong about serverless and vendor lock-in
- You are thinking about serverless costs all wrong
- Just how expensive is the full AWS SDK?
- Check-list for going live with API Gateway and Lambda
- How to choose the right API Gateway auth method
- CloudFormation protip: use !Sub instead of !Join
- AWS Lambda – should you have few monolithic functions or many single-purposed functions?
- Guys, we’re doing pagination wrong
- Top 10 Serverless framework best practices
- How to break the “senior engineer” career ceiling
- My advice to junior developers