Strategic laziness.
The Deferred datatype in Procrastinate.jl does one simple thing. It waits until the
last possible moment to compute an object. It is useful for expensive to compute items
in a struct that may or may not ever be required. It takes a return type and
zero-argument closure.
julia> using Procrastinate
julia> d = Deferred() do
# Some expensive function
println("Computing!")
return "result"
end
julia> d()
Computing!
"result"
julia> d()
"result"struct Demo
item1::Deferred
item2::Deferred
Demo(d1::Deferred, d2::Deferred) = new(d1,d2)
end
fn(n) = n ∈ (0, 1) ? 1 : fn(n-2) + fn(n-1) # slow!
n, str = 42, "It's a bird!"
dd = Demo(
Deferred() do
Base.sleep(2)
str
end,
Deferred(()->fn(n)) # takes a few seconds
)
dd.item1() # returns "It's a bird!" after a couple seconds
dd.item2() # returns 433494437 after a few seconds
dd.item1() # returns "It's a bird!" almost immediately
dd.item2() # returns 433494437 almost immediately