As my functional programming adventure continues, I come across terms I'm not familiar with. Today, we'll look at when to use a Discriminated Union vs Record Type.
I strongly believe on the best way to learn something is to teach it to someone else.
It will solidify your knowledge.
(I'm learning F# and before I become too good at it, I'd to share my beginner's notes with you. Hopefully, it helps you to understand F# and functional programming.)
Discriminated Union
Let's skip all the boring jargon out there. Here's the simplest explanation I could find
possible [data] values for which can be enumerated.
Some examples:
type Status =
| Active
| Inactive
| Disabled
type Answer =
| Yes
| No
Answer up above can only be Yes or No.
It can't be anything else other than those two specific values.
It seems to work similar to C# enums.
Record Type
Skipping all the jargon again:
[used] for complex data which is described by several properties, like a database record or some model entity
These are the equivalent of your classes in a language like C#. But I feel like they are more structs than classes.
Some examples:
type User = { FirstName: string; LastName : string; Age: Int; }
type Cookie = { Name: string; Color: string; }
When to use a Discriminated Union vs Record Type
Think of it as a Record is 'and', while a discriminated union is 'or'.
This is the key.
Record = and
Discriminated Union = or
Example:
type MyRecord = { myString: string
myInt: int }
The following value can either be a string OR an int, but not both:
type MyUnion =
| Int of int
| Str of string
Here's another discriminated union example in a fictitious game:
type Game =
| Title
| Ingame
| Endgame
You can only be in one area at the time.
You can't be in the Title screen and be Ingame.
You can't be in the Ingame and be at Endgame.
Think of this as options for your radio buttons.
Closing Thoughts
If you skipped all the way to the end, make sure you read the When to use a Discriminated Union vs Record Type section at the very least.
Discriminated Union sounds very intimidating. But think of it asL multiple options your value can be.
The simplest comparison is options for your radio buttons.
What do you think? How would you define a discriminated union and a record type in F#?
Originally posted at:
http://www.mindbodysouldeveloper.com/
Top comments (2)
This is a good explanation of the two types.
Both types are very useful on there own, but things get interesting when you combine them. Also, there are choices for how to combine them.
For example, in a card game of sorts is there a record type
Cardthat has a discriminated unionCardTypeor does the union contain the records?See the following:
or
I think it depends on how the cards are going to be used. If the second pattern is followed then every interaction with a card will first have to handle the card type. If you need the cost before the type something like the first pattern should work.
Excellent example. You are right, it depends how you are going to use your cards.
There is no silver bullet but it's always good to know that there are options available.
Thank you for sharing your thoughts on this.