If you’re reading this post, you probably know about F#’s Units of Measure already, it’s very useful when working with real-world units and adds extra safety to code that needs to work with and convert from one unit to another.
Here’s a quick snippet that shows you how to define and use units-of-measure:
This code outputs the following, note the units associated with the float values:
As you can see, units of measure can also be compounded by multiplication or division!
If you have a function that requires a int<m>, you won’t be able to call the function with a normal int, hence providing you with extra protection to ensure the correctness of your application because the unit of a numeric value is now a formal contract between a function and its caller:
Having said that, there are cases where you want to be able to convert between an int and an int<m>. For instance, to provide better interoperability with other .Net languages, as units-of-measure only exists in F# there’s no way to create a numeric value with units-of-measure in C# (that I’m aware of anyway).
To convert from int<m> to int (or any other numeric type) is easy, just do a straight cast:
Going the other way is slightly more tricky, you can’t use int<m> to cast an int to an int<m>, but you can either multiply the value with 1<m> or use the Int32WithMeasure method on the LanguagePrimitives core module:
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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.
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