Skip to main content

Units of Measure in F#

One of the nice features of F#, is the support for units of measure. This allows you to associate a unit of measure(e.g. liters, centimeters,...) to a type(typically floating point, integral and decimal types). Now the compiler becomes your friend and helps you avoid the unit mismatch errors that can occur.

With the compile time checking you now exactly the expected input or output type.

Built-in units

For some of the common unit types Microsoft has a unit library available in the FSharp.Data.UnitSystems.SI namespace. It includes SI units in both their symbol form (like m for meter) in the UnitSymbols subnamespace, and in their full name (like meter for meter) in the UnitNames subnamespace.

Here you can find the list of available units: https://fsharp.github.io/fsharp-core-docs/reference/fsharp-data-unitsystems-si-unitsymbols.html

To convert a unitless value to a value that has units, the easiest way is to multiply by a 1 or 1.0 value that is annotated with the appropriate units.

Custom units

You are not limited to the built-in types and can create your own using the following syntax:

[<Measure>] type unit-name [ = measure ]

Here is an example:

It is also possible to derive a unit from an existing unit type:

More information:

Labels:

Popular posts from this blog

Podman– Command execution failed with exit code 125

After updating WSL on one of the developer machines, Podman failed to work. When we took a look through Podman Desktop, we noticed that Podman had stopped running and returned the following error message: Error: Command execution failed with exit code 125 Here are the steps we tried to fix the issue: We started by running podman info to get some extra details on what could be wrong: >podman info OS: windows/amd64 provider: wsl version: 5.3.1 Cannot connect to Podman. Please verify your connection to the Linux system using `podman system connection list`, or try `podman machine init` and `podman machine start` to manage a new Linux VM Error: unable to connect to Podman socket: failed to connect: dial tcp 127.0.0.1:2655: connectex: No connection could be made because the target machine actively refused it. That makes sense as the podman VM was not running. Let’s check the VM: >podman machine list NAME         ...
Read more

Cache stampede: when our cache turned against us

While investigating some performance issues, we ran into an ASP.NET Core API that cached a fairly expensive aggregation query for 60 seconds. Under normal load, that was fine: one request rebuilds the cache, everyone else reads from it. Under peak load, dozens of requests would arrive in that same expiry window, all see a cache miss, and all fire the same expensive query in parallel. The database didn't like that. That was the moment when our caching layer stopped helping and started hurting. A burst of requests comes in at the same time, all miss the cache, and all go hammer the database or the downstream API at once. That's a cache stampede . The cache was supposed to protect our backend, and for a few hundred milliseconds it did the opposite. Why this happens IMemoryCache.GetOrCreate (and its async sibling) looks like it protects you, but it doesn't add any locking on its own. Look at the naive version: public async Task<Report> GetReportAsync(string key) ...
Read more

A complex system designed from scratch never works

A few years ago, I worked as an architect on a big mainframe rewrite. I still count it as one of my failures. Not because the technology was wrong, but because I couldn't convince the management team to simplify the approach. Years later, the organization is still struggling to get the new system up and running. I left the project at the time, because I couldn't put my name behind an approach that would take very long and cost a lot of money without a working system to show for it along the way. Gall’s Law That memory keeps coming back to me, because it's a textbook case of Gall's Law playing out in real life. Gall's Law , from John Gall's Systemantics , states it plainly: A complex system that works is invariably found to have evolved from a simple system that worked. A complex system designed from scratch never works, and it cannot be patched to make it work. You have to start over with a simple system that works. What does that mean in practice,...
Read more