Remove access of .data field on abstract types (#57)

---------

Co-authored-by: Stefan Krastanov <[email protected]>
Co-authored-by: Stefan Krastanov <[email protected]>

Author: akirakyle

CHANGELOG.md

@@ -1,7 +1,8 @@
 # News
 
-## dev
+## v0.4.0 - dev
 
+- **(breaking)** Move methods which access a `.data` field but are defined only on an abstract types to QuantumOpticsBase
 - Declare `mutual_information`, without any implemented methods.
 
 ## v0.3.10 - 2025-04-21

Project.toml

@@ -1,7 +1,7 @@
 name = "QuantumInterface"
 uuid = "5717a53b-5d69-4fa3-b976-0bf2f97ca1e5"
 authors = ["QuantumInterface.jl contributors"]
-version = "0.3.10"
+version = "0.4.0"
 
 [deps]
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"

src/QuantumInterface.jl

@@ -1,6 +1,6 @@
 module QuantumInterface
 
-import Base: ==, +, -, *, /, ^, length, one, exp, conj, conj!, transpose, copy
+import Base: ==, +, -, *, /, ^, length, one, exp, conj, conj!, transpose
 import LinearAlgebra: tr, ishermitian, norm, normalize, normalize!
 import Base: show, summary
 import SparseArrays: sparse, spzeros, AbstractSparseMatrix # TODO move to an extension

src/julia_base.jl

@@ -1,26 +1,27 @@
 # Common error messages
-arithmetic_unary_error(funcname, x::AbstractOperator) = throw(ArgumentError("$funcname is not defined for this type of operator: $(typeof(x)).\nTry to convert to another operator type first with e.g. dense() or sparse()."))
-arithmetic_binary_error(funcname, a::AbstractOperator, b::AbstractOperator) = throw(ArgumentError("$funcname is not defined for this combination of types of operators: $(typeof(a)), $(typeof(b)).\nTry to convert to a common operator type first with e.g. dense() or sparse()."))
-addnumbererror() = throw(ArgumentError("Can't add or subtract a number and an operator. You probably want 'op + identityoperator(op)*x'."))
+# We use these error messages instead of:
+# - MethodErrors, which are not very informative about the fact that there might very well be a convenient conversion to the desired type
+# - error hints, which are a bit too cumbersome to register for so many different types and functions
+# TODO use error hints instead of these custom error messages
+arithmetic_unary_error(funcname, x::AbstractOperator) = throw(ArgumentError("$funcname is not defined for this type of operator: $(typeof(x)).\nYou can try to convert to another operator type first, e.g. with `dense()` or `sparse()` from `QuantumOptics` or other type conversions from other packages."))
+arithmetic_binary_error(funcname, a::AbstractOperator, b::AbstractOperator) = throw(ArgumentError("$funcname is not defined for this combination of types of operators: $(typeof(a)), $(typeof(b)).\nYou can try to convert to another (common) operator type first, e.g. with `dense()` or `sparse()` from `QuantumOptics` or other type conversions from other packages."))
+addnumbererror() = throw(ArgumentError("Can't add or subtract a number and an operator. You probably want `op + identityoperator(op)*x`."))
 
 
 ##
 # States
 ##
 
--(a::T) where {T<:StateVector} = T(a.basis, -a.data) # FIXME issue #12
+-(a::StateVector) = arithmetic_unary_error("Negation", a)
 *(a::StateVector, b::Number) = b*a
-copy(a::T) where {T<:StateVector} = T(a.basis, copy(a.data)) # FIXME issue #12
 length(a::StateVector) = length(a.basis)::Int # FIXME issue #12
 basis(a::StateVector) = a.basis # FIXME issue #12
 directsum(x::StateVector...) = reduce(directsum, x)
 
 # Array-like functions
-Base.size(x::StateVector) = size(x.data) # FIXME issue #12
-@inline Base.axes(x::StateVector) = axes(x.data) # FIXME issue #12
+Base.size(x::StateVector) = length(basis(x))
 Base.ndims(x::StateVector) = 1
 Base.ndims(::Type{<:StateVector}) = 1
-Base.eltype(x::StateVector) = eltype(x.data) # FIXME issue #12
 
 # Broadcasting
 Base.broadcastable(x::StateVector) = x

src/julia_linalg.jl

@@ -17,7 +17,7 @@ tr(x::AbstractOperator) = arithmetic_unary_error("Trace", x)
 
 Norm of the given bra or ket state.
 """
-norm(x::StateVector) = norm(x.data) # FIXME issue #12
+norm(x::StateVector) = arithmetic_unary_error("norm", x)
 
 """
     normalize(x::StateVector)
@@ -31,7 +31,7 @@ normalize(x::StateVector) = x/norm(x)
 
 In-place normalization of the given bra or ket so that `norm(x)` is one.
 """
-normalize!(x::StateVector) = (normalize!(x.data); x) # FIXME issue #12
+normalize!(x::StateVector) = arithmetic_unary_error("normalize!", x)
 
 """
     normalize(op)