A record is a data structure for storing a fixed number of elements.
It has named fields and is similar to a struct in C.
If several fields are to be assigned the same value, the following construction can be used: . Since record expressions are expanded to tuple expressions, creating records and accessing record fields are allowed in guards.
However all subexpressions, for example, for field initiations, must be valid guard expressions as well.
Whenever you define a record type alias in Elm, you get the dotted getter functions for free.
Your setter functions however— to change something in your record (immutable-style of course)— you have to define for yourself.
You need to do this manually, or make your own setter function(s).
For this, I always follow a simple pattern, that has made updating records easier and my code a lot cleaner.
Now that we are all convinced that this is the behavior we want to implement, take a closer look at the code that implements it.
Hopefully these helpers can ease your pain of updating nesting records too.
If you just want to play with the pattern: you can tweak and run the demo below.
That's where the primary key ID of a database record and the attribute of its analogous Ruby object come in.
We need a way to select a Ruby object's analogous table row using some fixed and unique attribute.