If your have a type that represents a collection of values, adding a custom indexer gives you a natural way to index directly into the object using the .[ ] operator.
By adding a custom indexer here I’m now able to write code like this:
Also, as you may have noticed already, F# allows you to use non-integer parameters in your indexer! In this case, I’m using a tuple of int * string * int. You can use this indexer from your C# code too:
That’s pretty cool, but we can go a step further by allowing you to use slicers on our types too. To allow users to get all the notes associated with a range of years, e.g. from 1999 to 2009, let’s add a slicer:
So now we can do this:
Pretty awesome, right? But what if we want to refine our search criteria even more and let you specify a year range as well a range of months, e.g. get me all notes for April/May/June in the years 1999 to 2009. Thankfully, F# lets you define a two-dimensional slicer too:
This two-dimensional slicer allows me to query the calendar with a year range as well as a month range:
As you can see, indexers and slicers give the consumers of your code a much more intuitive way to interact with the data encapsulated in your type. Keep in mind though, that F# does not allow you to add slicer with more than two dimensions, but I think two-dimensional slicers should be good enough for most day-to-day requirements.
Swapped out my verbose optional argument handling with defaultArg as Arseny Kapoulkine pointed out in the comments.
Enjoy what you’re reading? Subscribe to my newsletter and get more content on AWS and serverless technologies delivered straight to your inbox.
I’m an AWS Serverless Hero and the author of Production-Ready Serverless. I have run production workload at scale in AWS for nearly 10 years and I have been an architect or principal engineer with a variety of industries ranging from banking, e-commerce, sports streaming to mobile gaming. I currently work as an independent consultant focused on AWS and serverless.
In this course, we’ll cover everything you need to know to use AWS Step Functions service effectively. Including basic concepts, HTTP and event triggers, activities, design patterns and best practices.
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.
- Lambda optimization tip – enable HTTP keep-alive
- You are thinking about serverless costs all wrong
- Many faced threats to Serverless security
- We can do better than percentile latencies
- I’m afraid you’re thinking about AWS Lambda cold starts all wrong
- Yubl’s road to Serverless
- AWS Lambda – should you have few monolithic functions or many single-purposed functions?
- AWS Lambda – compare coldstart time with different languages, memory and code sizes
- Guys, we’re doing pagination wrong