Discriminated unions are a powerful data structure to use when modelling a domain in an application.

The name of this data type varies between programming languages, for instance:

• F# calls itDiscriminated unions
• OCaml calls itVariants
• TypeScript calls itTagged Union Types some times, and other times discriminated unions
• Haskell calls itAlgebraic data types

Pattern matching and discriminated unions are great together and makes it really easy to express complex models in the code.

Here is a simple example to make a boolish type in F#:

typeAnswer=Yes|Noletresponseanswer=matchanswerwith|Yes->"Correct answer"|No->"Wrong answer"

One popular example in OOP is to show inheritance with aShape class. Here is an example but with discriminated unions instead:

typeShape=|Circleoffloat|Rectangleoffloat*float|SquareoffloatletcalculateAreashape=matchshapewith|Circle(radius)->Math.PI*radius*radius|Rectangle(width,height)->width*height|Square(side)->side*side

In other words:

Use discriminated unions for concise and type-safe representation of complex data structures, promoting clarity, pattern matching, and compiler-enforced correctness.

Happy hacking!