blocklengths when empty (#182)

* blocklengths when empty

* add tests

* Update blockaxis.jl

* v0.16.5

Author: dlfivefifty

Project.toml

@@ -1,6 +1,6 @@
 name = "BlockArrays"
 uuid = "8e7c35d0-a365-5155-bbbb-fb81a777f24e"
-version = "0.16.4"
+version = "0.16.5"
 
 [deps]
 ArrayLayouts = "4c555306-a7a7-4459-81d9-ec55ddd5c99a"

src/blockaxis.jl

@@ -60,7 +60,7 @@ _blocklengths2blocklasts(blocks) = cumsum(blocks) # extra level to allow changin
 
 _diff(a::AbstractVector) = diff(a)
 _diff(a::Tuple) = diff(collect(a))
-@inline blocklengths(a::BlockedUnitRange) = [first(a.lasts)-a.first+1; _diff(a.lasts)]
+@inline blocklengths(a::BlockedUnitRange) = isempty(a.lasts) ? _diff(a.lasts) : [first(a.lasts)-a.first+1; _diff(a.lasts)]
 
 length(a::BlockedUnitRange) = isempty(a.lasts) ? 0 : Integer(last(a.lasts)-a.first+1)
 

test/test_blockarrays.jl

@@ -555,4 +555,9 @@ end
         @test (a')[:,Block.(1:2)] isa Adjoint
         @test transpose(a)[:,Block.(1:2)] isa Transpose
     end
+
+    @testset "empty blocklengths" begin
+        A = BlockVector{Float64}(undef,Int[])
+        @test @inferred(isempty(blocklengths(axes(A,1))))
+    end
 end