Idea: Pre-allocating intermediate arrays

[tkf]

I've been thinking about writing a function cached (or allocate or optimize or something) such that

app = cached(@~ f.(A * B, C))

would be transformed to

app = @~ f.(materialize!(tmp, A * B), C)

with appropriate tmp array. This way, materialize!(dest, app) can be done without allocation. I think pre-allocations like this would be required between every boundary between Applied and Broadcasted, if you want to hoist out allocations.

A few questions:

• I see that there is a LazyArrays.cache function. Is it related to this idea?
• Does it make sense to have this in LazyArrays? Should it be developed outside?

[dlfivefifty]

cache is used to cache the entries of a lazy array, mostly for the infinite-dimensional case, e.g., C = cache(Zeros(∞)); C[100] = 5;.