zero for OneElement (#332)

* zero for OneElement

* Specialize iszero

* Specialize isone

* Return a OneElement instead of a Zero

src/oneelement.jl

@@ -115,6 +115,17 @@ Base.@propagate_inbounds function Base.setindex(A::AbstractZeros{T,N}, v, kj::Va
     OneElement(convert(T, v), kj, axes(A))
 end
 
+zero(A::OneElement) = OneElement(zero(A.val), A.ind, A.axes)
+
+iszero(A::OneElement) = iszero(getindex_value(A))
+
+function isone(A::OneElementMatrix)
+    lenA = length(A)
+    lenA == 0 && return true
+    lenA > 1 && return false
+    isone(getindex_value(A))
+end
+
 *(x::OneElement, b::Number) = OneElement(x.val * b, x.ind, x.axes)
 *(b::Number, x::OneElement) = OneElement(b * x.val, x.ind, x.axes)
 /(x::OneElement, b::Number) = OneElement(x.val / b, x.ind, x.axes)

test/runtests.jl

@@ -2501,6 +2501,28 @@ end
         @test A / (2 + 3.0im) === OneElement(val / (2 + 3.0im), (2,2), (3,4)) == B / (2 + 3.0im)
     end
 
+    @testset "zero/iszero" begin
+        v = OneElement(10, 3, 4)
+        @test v + zero(v) == v
+        @test typeof(zero(v)) == typeof(v)
+
+        @test !iszero(v)
+        @test iszero(OneElement(0, 3, 4))
+        @test iszero(OneElement(0, 5, 4))
+        @test iszero(OneElement(3, (2,2), (0,0)))
+        @test iszero(OneElement(3, (2,2), (1,2)))
+
+        v = OneElement(SMatrix{2,2}(1:4), 3, 4)
+        @test v + zero(v) == v
+        @test typeof(zero(v)) == typeof(v)
+    end
+
+    @testset "isone" begin
+        @test isone(OneElement(3, (0,0), (0,0)))
+        @test isone(OneElement(1, (1,1), (1,1)))
+        @test !isone(OneElement(2, (1,1), (1,1)))
+        @test !isone(OneElement(1, (2,2), (2,2)))
+    end
 
     @testset "tril/triu" begin
         for A in (OneElement(3, (4,2), (4,5)), OneElement(3, (2,3), (4,5)), OneElement(3, (3,3), (4,5)))