contains constant trait (#486)

* containsconstant trait

* traited Fun-Number promote_rule

* remove unused method

Author: jishnub

Project.toml

@@ -1,6 +1,6 @@
 name = "ApproxFunBase"
 uuid = "fbd15aa5-315a-5a7d-a8a4-24992e37be05"
-version = "0.8.34"
+version = "0.8.35"
 
 [deps]
 AbstractFFTs = "621f4979-c628-5d54-868e-fcf4e3e8185c"
@@ -20,6 +20,7 @@ IntervalSets = "8197267c-284f-5f27-9208-e0e47529a953"
 LazyArrays = "5078a376-72f3-5289-bfd5-ec5146d43c02"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 LowRankApprox = "898213cb-b102-5a47-900c-97e73b919f73"
+SimpleTraits = "699a6c99-e7fa-54fc-8d76-47d257e15c1d"
 SparseArrays = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"
 SpecialFunctions = "276daf66-3868-5448-9aa4-cd146d93841b"
 StaticArrays = "90137ffa-7385-5640-81b9-e52037218182"
@@ -45,6 +46,7 @@ Infinities = "0.1"
 IntervalSets = "0.5, 0.6, 0.7"
 LazyArrays = "0.20, 0.21, 0.22, 1"
 LowRankApprox = "0.2, 0.3, 0.4, 0.5"
+SimpleTraits = "0.9"
 SpecialFunctions = "0.10, 1.0, 2"
 StaticArrays = "0.12, 1.0"
 julia = "1.6"

src/ApproxFunBase.jl

@@ -3,7 +3,8 @@ using Base: AnyDict
 using Base, BlockArrays, BandedMatrices, BlockBandedMatrices, DomainSets,
               IntervalSets, SpecialFunctions, AbstractFFTs, FFTW,
               SpecialFunctions, DSP, DualNumbers, LinearAlgebra, SparseArrays,
-              LowRankApprox, FillArrays, InfiniteArrays, InfiniteLinearAlgebra
+              LowRankApprox, FillArrays, InfiniteArrays, InfiniteLinearAlgebra,
+              SimpleTraits
 
 import StaticArrays, Calculus
 using StaticArrays: SVector, @SArray, SArray

src/Fun.jl

@@ -216,8 +216,8 @@ one(::Type{Fun{S,T,VT}}) where {T,S<:Space,VT} = ones(T,S(AnyDomain()))
 zero(f::Fun) = zeros(cfstype(f), space(f))
 one(f::Fun) = ones(cfstype(f), space(f))
 
-cfstype(::Fun{S,T}) where {S,T} = T
-cfstype(::Type{Fun{S,T,VT}}) where {S,T,VT} = T
+cfstype(f::Fun) = cfstype(typeof(f))
+cfstype(::Type{<:Fun{<:Any,T}}) where {T} = T
 
 # Number and Array conform to the Fun interface
 cfstype(::Type{T}) where T<: Number = T

src/Space.jl

@@ -631,7 +631,7 @@ end
 ConstantSpace(d::Domain) = ConstantSpace{typeof(d),real(prectype(d))}(d)
 
 ConstantSpace(::Type{N},d::Domain) where {N<:Number} = ConstantSpace{typeof(d),real(N)}(d)
-ConstantSpace(::Type{N}) where {N<:Number} = ConstantSpace(N,AnyDomain())
+ConstantSpace(N::Type{<:Number}) = ConstantSpace(N,AnyDomain())
 ConstantSpace() = ConstantSpace(Float64)
 
 

src/Spaces/ConstantSpace.jl

@@ -31,18 +31,48 @@ coefficients(cfs::AbstractVector,::SequenceSpace) = cfs  # all vectors are conve
 
 ## Constant space defintions
 
+@traitdef ContainsConstant{X}
+@traitimpl ContainsConstant{X} <- containsconstant(X)
+
+containsconstant(@nospecialize(_)) = false
+
+promote_rule(TS1::Type{<:ConstantSpace}, TS2::Type{<:Space}) =
+    constspace_promote_rule(TS1, TS2)
+
+@traitfn function constspace_promote_rule(::Type{<:ConstantSpace},
+            B::Type{X}) where {X; !ContainsConstant{X}}
+    Union{}
+end
+@traitfn function constspace_promote_rule(::Type{<:ConstantSpace},
+            B::Type{X}) where {X; ContainsConstant{X}}
+    B
+end
+
+union_rule(A::ConstantSpace, B::Space) = constspace_union_rule(A, B)
+# TODO: this seems like it needs more thought
+@traitfn constspace_union_rule(A::ConstantSpace, B::X) where {X; !ContainsConstant{X}} =
+    ConstantSpace(domain(B))⊕B
+@traitfn constspace_union_rule(A::ConstantSpace, B::X) where {X; ContainsConstant{X}} = B
+
+promote_rule(TF::Type{<:Fun}, TN::Type{<:Number}) = fun_promote_rule(TF, TN)
+
+@traitfn fun_promote_rule(::Type{<:Fun{S,CT}},
+            ::Type{T}) where {T<:Number,CT,S; !ContainsConstant{S}} = Fun
+@traitfn function fun_promote_rule(::Type{<:Fun{S,CT}},
+            ::Type{T}) where {T<:Number,CT,S; ContainsConstant{S}}
+    ApproxFunBase.VFun{S,promote_type(CT,T)}
+end
+@traitfn fun_promote_rule(::Type{Fun{S}},
+            ::Type{T}) where {T<:Number,S; !ContainsConstant{S}} = Fun
+@traitfn function fun_promote_rule(::Type{<:Fun{S}},
+            ::Type{T}) where {T<:Number,S; ContainsConstant{S}}
+    ApproxFunBase.VFun{S,T}
+end
+
 # setup conversions for spaces that contain constants
 macro containsconstants(SP)
     esc(quote
-        ApproxFunBase.union_rule(A::(ApproxFunBase.ConstantSpace),B::$SP) = B
-        Base.promote_rule(A::Type{<:(ApproxFunBase.ConstantSpace)},B::Type{<:($SP)}) = B
-
-        Base.promote_rule(::Type{ApproxFunBase.Fun{S,V,VV}},::Type{T}) where {T<:Number,S<:$SP,V,VV} =
-        ApproxFunBase.VFun{S,promote_type(V,T)}
-        Base.promote_rule(::Type{ApproxFunBase.Fun{S}},::Type{T}) where {T<:Number,S<:$SP} = ApproxFunBase.VFun{S,T}
-        Base.promote_rule(::Type{ApproxFunBase.Fun{S,V,VV}},
-        ::Type{Fun{ApproxFunBase.ConstantSpace{ApproxFunBase.AnyDomain},T,VT}}) where {T,S<:$SP,V,VV,VT} =
-            ApproxFunBase.VFun{S,promote_type(V,T)}
+        ApproxFunBase.containsconstant(::Type{<:$SP}) = true
     end)
 end
 
@@ -78,7 +108,6 @@ Number(f::Fun) = strictconvert(Number, f)
 Base.promote_rule(::Type{Fun{CS}},::Type{T}) where {CS<:ConstantSpace,T<:Number} = Fun{CS,T}
 Base.promote_rule(::Type{Fun{CS,V}},::Type{T}) where {CS<:ConstantSpace,T<:Number,V} =
     Fun{CS,promote_type(T,V)}
-Base.promote_rule(::Type{IF},::Type{T}) where {T<:Number,IF<:Fun} = Fun
 
 
 # we know multiplication by constants preserves types
@@ -107,10 +136,6 @@ maxspace_rule(A::ZeroSpace,B::Space) = B
 Conversion(A::ZeroSpace,B::ZeroSpace) = ConversionWrapper(ZeroOperator(A,B))
 Conversion(A::ZeroSpace,B::Space) = ConversionWrapper(ZeroOperator(A,B))
 
-# TODO: this seems like it needs more thought
-union_rule(A::ConstantSpace,B::Space) = ConstantSpace(domain(B))⊕B
-
-
 ## Special Multiplication and Conversion for constantspace
 
 #  TODO: this is a special work around but really we want it to be blocks

test/SpacesTest.jl

@@ -198,6 +198,11 @@ using LinearAlgebra
             @test fs[1] == Fun(f1, sp)
             @test fs[2] == Fun(f2, sp)
         end
+
+        @testset "promote_rule" begin
+            F = Fun{typeof(PointSpace(1:3)), Float32}
+            @test ApproxFunBase.cfstype(F) == Float32
+        end
     end
 
     @testset "DiracSpace" begin