Fix NondecreasingIndices

src/Iteration/NondecreasingIndices.jl

@@ -41,6 +41,11 @@ julia> for v in NondecreasingIndices(4, 2)
 struct NondecreasingIndices
     n::Int
     m::Int
+
+    function NondecreasingIndices(n::Int, m::Int)
+        @assert n > 0 && m > 0 "require n > 0 and m > 0"
+        new(n, m)
+    end
 end
 
 Base.eltype(::Type{NondecreasingIndices}) = Vector{Int}
@@ -51,7 +56,8 @@ Base.length(ndi::NondecreasingIndices) = binomial(ndi.n + ndi.m - 1, ndi.m)
 # initialization
 function Base.iterate(ndi::NondecreasingIndices)
     v = ones(Int, ndi.m)
-    return (v, v)
+    next = ndi.n == 1 ? nothing : v
+    return (v, next)
 end
 
 # normal iteration

src/Iteration/StrictlyIncreasingIndices.jl

@@ -49,17 +49,15 @@ Base.length(sii::StrictlyIncreasingIndices) = binomial(sii.n, sii.m)
 # initialization
 function Base.iterate(sii::StrictlyIncreasingIndices)
     v = [1:sii.m;]
-    return (v, v)
+    next = sii.n == sii.m ? nothing : v
+    return (v, next)
 end
 
 # normal iteration
 function Base.iterate(sii::StrictlyIncreasingIndices, state::AbstractVector{Int})
     v = state
     i = sii.m
     diff = sii.n
-    if i == diff
-        return nothing
-    end
     while v[i] == diff
         i -= 1
         diff -= 1

test/Iteration/NondecreasingIndices.jl

@@ -1,7 +1,17 @@
 using ReachabilityBase.Iteration
 
 vectors = Vector{AbstractVector{Int}}()
-for v in NondecreasingIndices(2, 3)
+ndi = NondecreasingIndices(2, 3)
+@test length(ndi) == 4
+for v in ndi
     push!(vectors, copy(v))
 end
 @test vectors == [[1, 1, 1], [1, 1, 2], [1, 2, 2], [2, 2, 2]]
+
+vectors = Vector{AbstractVector{Int}}()
+ndi = NondecreasingIndices(1, 3)
+@test length(ndi) == 1
+for v in ndi
+    push!(vectors, copy(v))
+end
+@test vectors == [[1, 1, 1]]

test/Iteration/StrictlyIncreasingIndices.jl

@@ -1,7 +1,17 @@
 using ReachabilityBase.Iteration
 
 vectors = Vector{AbstractVector{Int}}()
-for v in StrictlyIncreasingIndices(5, 4)
+sii = StrictlyIncreasingIndices(5, 4)
+@test length(sii) == 5
+for v in sii
     push!(vectors, copy(v))
 end
 @test vectors == [[1, 2, 3, 4], [1, 2, 3, 5], [1, 2, 4, 5], [1, 3, 4, 5], [2, 3, 4, 5]]
+
+vectors = Vector{AbstractVector{Int}}()
+sii = StrictlyIncreasingIndices(2, 2)
+@test length(sii) == 1
+for v in sii
+    push!(vectors, copy(v))
+end
+@test vectors == [[1, 2]]