Implement memoization #6887
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Implement memoization #6887
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soronpo
reviewed
Jul 21, 2019
| in the parentheses is computed only the first time and is cached for subsequent recalculuations. | ||
| The memoized program expands to the following code: | ||
| ``` | ||
| class C(x: T) { |
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missing [T] (and in all other examples)
|
(I need this now! 😄) class C[T](x: T) {
var someState : Boolean = false //somewhere this is modified
def costly(x : T) : Int = {
if (someState) ???
else ???
}
def f(y: Int) = memo(costly(x)) * y
}How do we prevent this? Is there a way for the compiler to verify the function is pure? |
|
@soronpo There is not currently a mechanism to indicate that a function is pure. There might be in the future, but it will take a while to get there. The problem you outline is exactly the same for a lazy val, so not specific to |
Implement `memo(...)` function which caches its argument on first evaluation and re-uses the cached value afterwards. The cache is placed next to the method enclosing the memo(...) call. `memo` is a member of package `compiletime`.
Maybe we should always set the positions of these generated definitions automatically from the symbol's span. It's an easy trap to fall into.
Stale symbol errors can happen when inspecting symbols while comparing the trees before and after pickling.
... and also make it work on several nested levels together.
Restricting `entered` and `enteredAfter` to class members is more a trap to fall into than a helpful check.
|
Superseded by #6967 |
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Implement
memo(...)function which caches its argument on first evaluationand re-uses the cached value afterwards. The cache is placed next to the
method enclosing the memo(...) call.
memois a member of packagecompiletime.