Implement promote_operation

src/arithmetic.jl

@@ -1,5 +1,14 @@
-_coeff_type(X::AlgebraElement) = eltype(X)
-_coeff_type(a) = typeof(a)
+_coeff_type(::Type{A}) where {A<:AlgebraElement} = eltype(A)
+_coeff_type(a::Type) = a
+_coeff_type(a) = _coeff_type(typeof(a))
+
+function algebra_promote_operation(op, args::Vararg{Type,N}) where {N}
+    T = MA.promote_operation(op, _coeff_type.(args)...)
+    if args[2] <: AlgebraElement && MA.promote_operation(coeffs, args[2]) <: DenseArray # what a hack :)
+        return similar_type(args[2], T)
+    end
+    return similar_type(args[1], T)
+end
 
 function _preallocate_output(op, args::Vararg{Any,N}) where {N}
     T = MA.promote_operation(op, _coeff_type.(args)...)
@@ -18,25 +27,31 @@ Base.:(//)(X::AlgebraElement, a::Number) = 1 // a * X
 function Base.:-(X::AlgebraElement)
     return MA.operate_to!(_preallocate_output(*, X, -1), -, X)
 end
+function MA.promote_operation(::typeof(*), ::Type{T}, ::Type{A}) where {T<:Number, A<:AlgebraElement}
+    return algebra_promote_operation(*, A, T)
+end
 function Base.:*(a::Number, X::AlgebraElement)
     return MA.operate_to!(_preallocate_output(*, X, a), *, X, a)
 end
 function Base.:div(X::AlgebraElement, a::Number)
     return MA.operate_to!(_preallocate_output(div, X, a), div, X, a)
 end
 
-function Base.:+(X::AlgebraElement, Y::AlgebraElement)
-    return MA.operate_to!(_preallocate_output(+, X, Y), +, X, Y)
-end
-function Base.:-(X::AlgebraElement, Y::AlgebraElement)
-    return MA.operate_to!(_preallocate_output(-, X, Y), -, X, Y)
-end
-function Base.:*(X::AlgebraElement, Y::AlgebraElement)
-    return MA.operate_to!(_preallocate_output(*, X, Y), *, X, Y)
+for op in [:+, :-, :*]
+    @eval begin
+        function MA.promote_operation(::typeof($op), ::Type{X}, ::Type{Y}) where {X<:AlgebraElement,Y<:AlgebraElement}
+            return algebra_promote_operation($op, X, Y)
+        end
+        function Base.$op(X::AlgebraElement, Y::AlgebraElement)
+            return MA.operate_to!(_preallocate_output($op, X, Y), $op, X, Y)
+        end
+    end
 end
+
 function Base.:*(args::Vararg{AlgebraElement,N}) where {N}
     return MA.operate_to!(_preallocate_output(*, args...), *, args...)
 end
+
 Base.:^(a::AlgebraElement, p::Integer) = Base.power_by_squaring(a, p)
 
 # mutable API

src/coefficients.jl

@@ -38,6 +38,9 @@ Base.iszero(ac::AbstractCoefficients) = isempty(keys(ac))
 
 Base.similar(ac::AbstractCoefficients) = similar(ac, valtype(ac))
 
+similar_type(::Type{<:Vector}, ::Type{T}) where {T} = Vector{T}
+similar_type(::Type{<:SparseArrays.SparseVector{C,I}}, ::Type{T}) where {C,I,T} = SparseArrays.SparseVector{T,I}
+
 """
     canonical(ac::AbstractCoefficients)
 Compute the canonical form of `ac` (e.g. grouping coefficients together, etc).

src/sparse_coeffs.jl

@@ -47,6 +47,13 @@ _similar(x::Tuple, ::Type{T}) where {T} = Vector{T}(undef, length(x))
 _similar(x) = similar(x)
 _similar(x, ::Type{T}) where {T} = similar(x, T)
 
+_similar_type(::Type{<:Tuple}, ::Type{T}) where {T} = Vector{T}
+_similar_type(::Type{V}, ::Type{T}) where {V,T} = similar_type(V, T)
+
+function similar_type(::Type{SparseCoefficients{K,V,Vk,Vv}}, ::Type{T}) where {K,V,Vk,Vv,T}
+    return SparseCoefficients{K,T,_similar_type(Vk, K),_similar_type(Vv, T)}
+end
+
 function Base.similar(s::SparseCoefficients, ::Type{T} = valtype(s)) where {T}
     return SparseCoefficients(_similar(s.basis_elements), _similar(s.values, T))
 end

src/types.jl

@@ -25,6 +25,7 @@ struct StarAlgebra{O,T,B<:AbstractBasis{T}} <: AbstractStarAlgebra{O,T}
 end
 
 basis(A::StarAlgebra) = A.basis
+MA.promote_operation(::typeof(basis), ::Type{StarAlgebra{O,T,B}}) where {O,T,B} = B
 object(A::StarAlgebra) = A.object
 
 struct AlgebraElement{A,T,V} <: MA.AbstractMutable
@@ -33,14 +34,21 @@ struct AlgebraElement{A,T,V} <: MA.AbstractMutable
 end
 
 Base.parent(a::AlgebraElement) = a.parent
-Base.eltype(a::AlgebraElement) = valtype(coeffs(a))
+Base.eltype(::Type{A}) where {A<:AlgebraElement} = valtype(MA.promote_operation(coeffs, A))
+Base.eltype(a::AlgebraElement) = eltype(typeof(a))
+function MA.promote_operation(::typeof(coeffs), ::Type{AlgebraElement{A,T,V}}) where {A,T,V}
+    return V
+end
 coeffs(a::AlgebraElement) = a.coeffs
 function coeffs(x::AlgebraElement, b::AbstractBasis)
     return coeffs(coeffs(x), basis(x), b)
 end
 function adjoint_coeffs(a::AlgebraElement, target::AbstractBasis)
     return adjoint_coeffs(coeffs(a), target, basis(a))
 end
+function MA.promote_operation(::typeof(basis), ::Type{<:AlgebraElement{A}}) where {A}
+    return MA.promote_operation(basis, A)
+end
 basis(a::AlgebraElement) = basis(parent(a))
 
 function AlgebraElement(coeffs, A::AbstractStarAlgebra)
@@ -106,6 +114,10 @@ end
 
 (A::AbstractStarAlgebra)(x::Number) = x * one(A)
 
+function similar_type(::Type{AlgebraElement{A,T,V}}, ::Type{C}) where {A,T,V,C}
+    return AlgebraElement{A,C,similar_type(V, C)}
+end
+
 function Base.similar(X::AlgebraElement, T = eltype(X))
     return AlgebraElement(similar(coeffs(X), T), parent(X))
 end

test/caching_allocations.jl

@@ -8,6 +8,12 @@
     end
 end
 
+function _test_op(op, a, b)
+    result = @inferred op(a, b)
+    @test typeof(result) == MA.promote_operation(op, typeof(a), typeof(b))
+    return result
+end
+
 @testset "FixedBasis caching && allocations" begin
     alph = [:a, :b, :c]
     A★ = FreeWords(alph)
@@ -88,8 +94,10 @@ end
         (1,),
     )
     Z = AlgebraElement(z, fRG)
-    @test Z + Z == 2 * Z
-    @test Z + Z == Y + Y
-    @test Y + Z == Y + Y
-    @test Z + Y == Y + Y
+    @test _test_op(+, Z, Z) == _test_op(*, 2, Z)
+    @test _test_op(+, Z, Z) == _test_op(+, Y, Y)
+    @test _test_op(+, Y, Z) == _test_op(+, Y, Y)
+    @test _test_op(+, Z, Y) == _test_op(+, Y, Y)
+    @test _test_op(-, Z, Z) == _test_op(*, 0, Z)
+    @test _test_op(-, Z, Z) == _test_op(-, Y, Z)
 end

test/constructors.jl

@@ -13,6 +13,7 @@ end
     A★ = FreeWords(alph)
     B = SA.DiracBasis(A★)
     RG = StarAlgebra(A★, B)
+    @test typeof(@inferred basis(RG)) == MA.promote_operation(basis, typeof(RG))
 
     @test typeof(zero(RG)) == typeof(RG(0))
     @test typeof(one(RG)) == typeof(RG(1))
@@ -33,6 +34,8 @@ end
     @test AlgebraElement(x, RG) isa AlgebraElement
 
     X = AlgebraElement(x, RG)
+    @test typeof(@inferred coeffs(X)) == MA.promote_operation(coeffs, typeof(X))
+    @test typeof(@inferred basis(X)) == MA.promote_operation(basis, typeof(X))
 
     @test AlgebraElement{Float64}(X) isa AlgebraElement
     Y = AlgebraElement{Float64}(X)