Units of measure in F#

A very interesting feature of F# – besides many others – is that we can assign a unit of measure to a variable value. These units of measure are located in the Microsoft.FSharp.Data.UnitSystems.SI.UnitNames namespace. As the namespace suggests the units are taken from the international system of units.

They are surrounded with angled brackets in code. Here’s an example:

open Microsoft.FSharp.Data.UnitSystems.SI.UnitNames
let meterValue = 100
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We can easily define our own units of measure that are not part of the namespace. The following example shows the “pound” type and how we can convert it to kilos:

namespace units

module Units =
open Microsoft.FSharp.Data.UnitSystems.SI.UnitNames

[]
type pound =
static member toKilos = 0.453592

let asKilos pounds:float = pounds * pound.toKilos

.
.
.
let converted = Units.asKilos 1.
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“converted” will be 0.453592 as expected.

View all F# related articles here.