Procrastinate.jl

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.

Minimal Example

julia> using Procrastinate
julia> d = Deferred() do
    # Some expensive function
    println("Computing!")
    return "result"
end
julia> d()
Computing!
"result"
julia> d()
"result"

More typical usage

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