narrow array conversions. fixes #26294, fixes #26178.

Not all array types can convert from any AbstractArray via a
1-argument constructor call.

Author: JeffBezanson

base/abstractarray.jl

@@ -12,7 +12,8 @@ Supertype for `N`-dimensional arrays (or array-like types) with elements of type
 AbstractArray
 
 convert(::Type{T}, a::T) where {T<:AbstractArray} = a
-convert(::Type{T}, a::AbstractArray) where {T<:AbstractArray} = T(a)
+convert(::Type{AbstractArray{T}}, a::AbstractArray) where {T} = AbstractArray{T}(a)
+convert(::Type{AbstractArray{T,N}}, a::AbstractArray{<:Any,N}) where {T,N} = AbstractArray{T,N}(a)
 
 if nameof(@__MODULE__) === :Base  # avoid method overwrite
 # catch undefined constructors before the deprecation kicks in

base/array.jl

@@ -413,8 +413,7 @@ oneunit(x::AbstractMatrix{T}) where {T} = _one(oneunit(T), x)
 
 ## Conversions ##
 
-# arises in similar(dest, Pair{Union{},Union{}}) where dest::Dict:
-convert(::Type{Vector{Union{}}}, a::Vector{Union{}}) = a
+convert(::Type{T}, a::AbstractArray) where {T<:Array} = a isa T ? a : T(a)
 
 promote_rule(a::Type{Array{T,n}}, b::Type{Array{S,n}}) where {T,n,S} = el_same(promote_type(T,S), a, b)
 

base/bitarray.jl

@@ -532,6 +532,8 @@ julia> BitArray(x+y == 3 for x = 1:2 for y = 1:3)
 """
 BitArray(itr) = gen_bitarray(IteratorSize(itr), itr)
 
+convert(T::Type{<:BitArray}, a::AbstractArray) = a isa T ? a : T(a)
+
 # generic constructor from an iterable without compile-time info
 # (we pass start(itr) explicitly to avoid a type-instability with filters)
 gen_bitarray(isz::IteratorSize, itr) = gen_bitarray_from_itr(itr, start(itr))

base/range.jl

@@ -97,6 +97,8 @@ abstract type AbstractRange{T} <: AbstractArray{T,1} end
 RangeStepStyle(::Type{<:AbstractRange}) = RangeStepIrregular()
 RangeStepStyle(::Type{<:AbstractRange{<:Integer}}) = RangeStepRegular()
 
+convert(::Type{T}, r::AbstractRange) where {T<:AbstractRange} = r isa T ? r : T(r)
+
 ## ordinal ranges
 
 abstract type OrdinalRange{T,S} <: AbstractRange{T} end

stdlib/LinearAlgebra/src/bidiag.jl

@@ -172,6 +172,8 @@ Bidiagonal{T}(A::Bidiagonal) where {T} =
 # When asked to convert Bidiagonal to AbstractMatrix{T}, preserve structure by converting to Bidiagonal{T} <: AbstractMatrix{T}
 AbstractMatrix{T}(A::Bidiagonal) where {T} = convert(Bidiagonal{T}, A)
 
+convert(T::Type{<:Bidiagonal}, m::AbstractMatrix) = m isa T ? m : T(m)
+
 broadcast(::typeof(big), B::Bidiagonal) = Bidiagonal(big.(B.dv), big.(B.ev), B.uplo)
 
 # For B<:Bidiagonal, similar(B[, neweltype]) should yield a Bidiagonal matrix.

stdlib/LinearAlgebra/src/special.jl

@@ -58,6 +58,15 @@ Tridiagonal(A::AbstractTriangular) =
         throw(ArgumentError("matrix cannot be represented as Tridiagonal"))
 
 
+const ConvertibleSpecialMatrix = Union{Diagonal,Bidiagonal,SymTridiagonal,Tridiagonal,AbstractTriangular}
+
+convert(T::Type{<:Diagonal},       m::ConvertibleSpecialMatrix) = m isa T ? m : T(m)
+convert(T::Type{<:SymTridiagonal}, m::ConvertibleSpecialMatrix) = m isa T ? m : T(m)
+convert(T::Type{<:Tridiagonal},    m::ConvertibleSpecialMatrix) = m isa T ? m : T(m)
+
+convert(T::Type{<:LowerTriangular}, m::Union{LowerTriangular,UnitLowerTriangular}) = m isa T ? m : T(m)
+convert(T::Type{<:UpperTriangular}, m::Union{UpperTriangular,UnitUpperTriangular}) = m isa T ? m : T(m)
+
 # Constructs two method definitions taking into account (assumed) commutativity
 # e.g. @commutative f(x::S, y::T) where {S,T} = x+y is the same is defining
 #     f(x::S, y::T) where {S,T} = x+y

stdlib/LinearAlgebra/src/symmetric.jl

@@ -163,6 +163,9 @@ for (S, H) in ((:Symmetric, :Hermitian), (:Hermitian, :Symmetric))
     end
 end
 
+convert(T::Type{<:Symmetric}, m::Union{Symmetric,Hermitian}) = m isa T ? m : T(m)
+convert(T::Type{<:Hermitian}, m::Union{Symmetric,Hermitian}) = m isa T ? m : T(m)
+
 const HermOrSym{T,S} = Union{Hermitian{T,S}, Symmetric{T,S}}
 const RealHermSymComplexHerm{T<:Real,S} = Union{Hermitian{T,S}, Symmetric{T,S}, Hermitian{Complex{T},S}}
 const RealHermSymComplexSym{T<:Real,S} = Union{Hermitian{T,S}, Symmetric{T,S}, Symmetric{Complex{T},S}}

stdlib/LinearAlgebra/test/diagonal.jl

@@ -27,6 +27,8 @@ srand(1)
             @test Diagonal{elty}(x)::Diagonal{elty,typeof(x)} == DM
             @test Diagonal{elty}(x).diag === x
         end
+        # issue #26178
+        @test_throws MethodError convert(Diagonal, [1, 2, 3, 4])
     end
 
     @testset "Basic properties" begin

stdlib/SharedArrays/src/SharedArrays.jl

@@ -358,6 +358,8 @@ function SharedArray{TS,N}(A::Array{TA,N}) where {TS,TA,N}
     copyto!(S, A)
 end
 
+convert(T::Type{<:SharedArray}, a::Array) = T(a)
+
 function deepcopy_internal(S::SharedArray, stackdict::IdDict)
     haskey(stackdict, S) && return stackdict[S]
     R = SharedArray{eltype(S),ndims(S)}(size(S); pids = S.pids)

stdlib/SparseArrays/src/sparsematrix.jl

@@ -412,6 +412,8 @@ function Matrix(S::SparseMatrixCSC{Tv}) where Tv
 end
 Array(S::SparseMatrixCSC) = Matrix(S)
 
+convert(T::Type{<:SparseMatrixCSC}, m::AbstractMatrix) = m isa T ? m : T(m)
+
 float(S::SparseMatrixCSC) = SparseMatrixCSC(S.m, S.n, copy(S.colptr), copy(S.rowval), float.(S.nzval))
 complex(S::SparseMatrixCSC) = SparseMatrixCSC(S.m, S.n, copy(S.colptr), copy(S.rowval), complex(copy(S.nzval)))
 

stdlib/SparseArrays/src/sparsevector.jl

@@ -420,6 +420,10 @@ SparseVector{Tv,Ti}(s::SparseVector) where {Tv,Ti} =
 SparseVector{Tv}(s::SparseVector{<:Any,Ti}) where {Tv,Ti} =
     SparseVector{Tv,Ti}(s.n, s.nzind, convert(Vector{Tv}, s.nzval))
 
+convert(T::Type{<:SparseVector}, m::AbstractVector) = m isa T ? m : T(m)
+
+convert(T::Type{<:SparseVector}, m::SparseMatrixCSC) = T(m)
+convert(T::Type{<:SparseMatrixCSC}, v::SparseVector) = T(v)
 
 ### copying
 function prep_sparsevec_copy_dest!(A::SparseVector, lB, nnzB)

stdlib/SuiteSparse/src/cholmod.jl

@@ -1082,6 +1082,7 @@ function SparseMatrixCSC{Tv,SuiteSparse_long}(A::Sparse{Tv}) where Tv
         return B
     end
 end
+
 function (::Type{Symmetric{Float64,SparseMatrixCSC{Float64,SuiteSparse_long}}})(A::Sparse{Float64})
     s = unsafe_load(pointer(A))
     if !issymmetric(A)
@@ -1099,6 +1100,8 @@ function (::Type{Symmetric{Float64,SparseMatrixCSC{Float64,SuiteSparse_long}}})(
         return B
     end
 end
+convert(T::Type{Symmetric{Float64,SparseMatrixCSC{Float64,SuiteSparse_long}}}, A::Sparse{Float64}) = T(A)
+
 function Hermitian{Tv,SparseMatrixCSC{Tv,SuiteSparse_long}}(A::Sparse{Tv}) where Tv<:VTypes
     s = unsafe_load(pointer(A))
     if !ishermitian(A)
@@ -1116,6 +1119,8 @@ function Hermitian{Tv,SparseMatrixCSC{Tv,SuiteSparse_long}}(A::Sparse{Tv}) where
         return B
     end
 end
+convert(T::Type{Hermitian{Tv,SparseMatrixCSC{Tv,SuiteSparse_long}}}, A::Sparse{Tv}) where {Tv<:VTypes} = T(A)
+
 function sparse(A::Sparse{Float64}) # Notice! Cannot be type stable because of stype
     s = unsafe_load(pointer(A))
     if s.stype == 0