I saw a message come across about Memoization, and I thought of using a
slightly different approach for similar benefit.
I commonly want to store the result of a complex calculation in a private
variable in a struct to avoid recalculation cost… but now I have to mark that
calculation as *mutating* even though it isn’t really mutating in the semantic
sense (since it will have the same value). It is an implementation detail
leaking out… the caller shouldn’t care if I am memoizing.
Also, my attempt to speed things up may have actually slowed things down, since
a bunch of other stuff had to be copied...
It would be nice to mark a calculated property of a struct as “memo" so that
the calculation result is stored… but the calculation shouldn’t need to be
marked as mutable (unless it actually mutates other things). That memo should
be automatically cleared whenever an actual mutating method is called on the
struct.
Ideally, the compiler would eventually be smart enough to only clear the memos
when properties used in the calculations change, but I think just clearing it
whenever the struct is mutated is a good first step.
struct MyStruct {
var a:Int
var b:Int
memo var c {
//Complex calculation here
}
}
let s = MyStruct(a:2, b:3)
print(s.c) // result of c is automatically memoized
print(s.c) // returns memoized result
s.a = 5 //This clears the memo for c as it may affect the calculation
print(s.c) // New result of c is automatically memoized
The other alternative is to do things manually. Letting the programmer declare
special private variables on a struct that are allowed to mutate without the
“mutating” key word. That is potentially more powerful, but also more error
prone. I prefer the set-it-and-forget-it approach.
If “memo" is the wrong word for this, I am completely open to calling it
something else. I would really like to see this functionality in Swift 3
though (whatever it is called).
Thanks,
Jon_______________________________________________
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