once.md

Define a function such that it only executes its body once. The value from first execution is memoized at the module level.

module X

export once
let x = Ref{Any}()
    global function once(f::Function)
        isassigned(x) && return x[]
        x[] = f()
        return x[]
    end
end

end #module

REPL:

julia> using .X: once

julia> once() do
           println("cool")
           1
       end
cool
1

julia> once() do
           println("cool")
           1
       end
1