Unified ModeMap Type (#330)

1. Resolve unoccupied_modes method test failed when FermiFS is
   constructed with SortedParticleList

Author: lch

src/BitStringAddresses/fermifs.jl

@@ -132,7 +132,10 @@ num_occupied_modes(::FermiFS{N}) where {N} = N
 occupied_modes(a::FermiFS{N,<:Any,S}) where {N,S} = FermiOccupiedModes{N,S}(a.bs)
 
 num_unoccupied_modes(::FermiFS{N,M}) where {N,M} = M - N
-unoccupied_modes(a::FermiFS{N,M,S}) where {N,M,S} = FermiUnoccupiedModes{M - N,S}(~a.bs)
+function unoccupied_modes(a::FermiFS{N,M,S}) where {N,M,S}
+    s = ~a.bs
+    FermiUnoccupiedModes{M - N,typeof(s)}(s)
+end
 
 """
     unoccupied_mode_map(addr::FermiFS) <: AbstractVector

src/BitStringAddresses/fockaddress.jl

@@ -694,7 +694,7 @@ Base.eltype(::FermiOccupiedModes) = FermiFSIndex
 """
     FermiUnoccupiedModes{N,S<:BitString}
 
-Iterator over unoccupied modes in address. `N` is the number of fermions. See [`unoccupied_modes`](@ref).
+Iterator over unoccupied modes in address. `N` is the number of unoccupied orbitals. See [`unoccupied_modes`](@ref).
 """
 struct FermiUnoccupiedModes{N,S} <: ModeIterator
     storage::S

src/BitStringAddresses/sortedparticlelist.jl

@@ -277,3 +277,23 @@ function Base.iterate(fom::FermiOccupiedModes{<:Any,<:SortedParticleList}, i=1)
         return FermiFSIndex(res...), i
     end
 end
+
+import Base.:~
+function ~(ss::SortedParticleList{N,M,T}) where {N,M,T}
+    ss
+end
+Base.length(::FermiUnoccupiedModes{N,<:SortedParticleList}) where {N} = N
+function Base.iterate(fum::FermiUnoccupiedModes{<:Any,<:SortedParticleList{N,M}}, state=(1, 1)) where {N,M}
+    if isnothing(state)
+        return nothing
+    else
+        i, j = state
+        while i ∈ fum.storage.storage
+            i += 1
+        end
+        if i > M
+            return nothing
+        end
+        return FermiFSIndex(0, i, i - 1), (i + 1, j + 1)
+    end
+end