Swift function vs lazy var vs computed property – difference?

lazy vars are actually stored properties, so you can’t put it in extensions or anywhere stored properties are not allowed.
The getter for computed properties is run every time you refer to that property. This can be significant especially if the getter is time-consuming or has side-effects to other parts of the code.
The getter for lazy vars are only run when the property is first referred to and never again.
lazy vars are variables. You can mutate them.
Computed properties can optionally have a setter, so sometimes they are read-only.
Using a function like that is very similar to a read only computed property. You just have to add () when getting its value.