Allow destructure to make an empty vector (#68)

* allow destructure to make an empty vector

* bump version, rm undef exports

* change to Bool[]

Author: mcabbott

Project.toml

@@ -1,7 +1,7 @@
 name = "Optimisers"
 uuid = "3bd65402-5787-11e9-1adc-39752487f4e2"
 authors = ["Mike J Innes <[email protected]>"]
-version = "0.2.2" 
+version = "0.2.3"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"

src/Optimisers.jl

@@ -6,7 +6,7 @@ using LinearAlgebra
 include("interface.jl")
 
 include("destructure.jl")
-export destructure, total, total2
+export destructure
 
 include("rules.jl")
 export Descent, ADAM, Momentum, Nesterov, RMSProp,

src/destructure.jl

@@ -64,6 +64,7 @@ function _flatten(x)
     len[] = o + length(y)
     o
   end
+  isempty(arrays) && return Bool[], off, 0
   reduce(vcat, arrays), off, len[]
 end
 

test/destructure.jl

@@ -220,3 +220,24 @@ tmp1
 @test tmp2 isa Vector{<:ForwardDiff.Dual}
 
 =#
+
+@testset "empty, issue 67" begin
+    m0 = (nothing, missing, isempty)
+    @test destructure(m0)[1] isa Vector{<:Real}
+    v0, re0 = destructure(m0)
+    @test re0(Float32[]) === m0
+    @test_throws DimensionMismatch re0([1])
+
+    # This is an elaborate way of checking that it doesn't cause promotions, even of small floats:
+    m01 = [(x=nothing, y=0), (x=Float16[1, 2], y=Float16[3])]
+    v01, _ = destructure(m01)
+    v012 = vcat(destructure(m01[1])[1], destructure(m01[2])[1])
+    @test v01 == v012
+    @test v012 isa Vector{Float16}
+
+    y, bk = Zygote.pullback(x -> sum(destructure(x)[1]), ("a", :beta))
+    @test bk(1.0) == (nothing,)
+    # Zygote regards 3,4 as differentiable, but Optimisers does not regard them as parameters:
+    y, bk = Zygote.pullback(x -> sum(destructure(x)[1]), (3, 4))
+    @test bk(1.0) == (nothing,)
+end