Add function interface for relevant properties of each basis

Author: akirakyle

src/QuantumInterface.jl

@@ -14,6 +14,32 @@ an [`IncompatibleBases`](@ref) error is thrown.
 """
 function basis end
 
+"""
+    fullbasis(a)
+
+Return the full basis of an object.
+
+Returns subtype of `Basis` when a is a subtype of `StateVector`.
+Returns a subtype of `OperatorBasis` a is a subtype of `AbstractOperator`.
+Returns a subtype of `SuperOperatorBasis` when a is a subtype of `AbstractSuperOperator`.
+"""
+function fullbasis end
+
+"""
+    length(b::Basis)
+
+Total dimension of the Hilbert space.
+"""
+function length end
+
+function bases end
+
+function spinnumber end
+
+function cutoff end
+
+function offset end
+
 ##
 # Standard methods
 ##

src/bases.jl

@@ -39,6 +39,7 @@ end
 CompositeBasis(bases) = CompositeBasis([length(b) for b ∈ bases], bases)
 CompositeBasis(bases::Basis...) = CompositeBasis((bases...,))
 CompositeBasis(bases::Vector) = CompositeBasis((bases...,))
+bases(b::CompositeBasis) = b.bases
 
 Base.:(==)(b1::T, b2::T) where T<:CompositeBasis = equal_shape(b1.shape, b2.shape)
 
@@ -258,6 +259,8 @@ struct FockBasis{T} <: Basis
         new{T}([N-offset+1], N, offset)
     end
 end
+cutoff(b::FockBasis) = b.N
+offset(b::FockBasis) = b.offset
 
 Base.:(==)(b1::FockBasis, b2::FockBasis) = (b1.N==b2.N && b1.offset==b2.offset)
 
@@ -323,6 +326,7 @@ struct SpinBasis{S,T} <: Basis
 end
 SpinBasis(spinnumber::Rational) = SpinBasis{spinnumber}(spinnumber)
 SpinBasis(spinnumber) = SpinBasis(convert(Rational{Int}, spinnumber))
+spinnumber(b::SpinBasis) = b.spinnumber
 
 Base.:(==)(b1::SpinBasis, b2::SpinBasis) = b1.spinnumber==b2.spinnumber