deprecate convert-to-construct fallback

Author: JeffBezanson

NEWS.md

@@ -17,6 +17,10 @@ Language changes
   * The syntax for parametric methods, `function f{T}(x::T)`, has been
     changed to `function f(x::T) where {T}` ([#11310]).
 
+  * The fallback constructor that calls `convert` is deprecated. Instead, new types should
+    prefer to define constructors, and add `convert` methods that call those constructors
+    only as necessary ([#15120]).
+
   * The syntax `1.+2` is deprecated, since it is ambiguous: it could mean either
     `1 .+ 2` (the current meaning) or `1. + 2` ([#19089]).
 

base/abstractarray.jl

@@ -11,6 +11,17 @@ 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)
+
+if module_name(@__MODULE__) === :Base  # avoid method overwrite
+# catch undefined constructors before the deprecation kicks in
+# TODO: remove when deprecation is removed
+function (::Type{T})(arg) where {T<:AbstractArray}
+    throw(MethodError(T, (arg,)))
+end
+end
+
 """
     size(A::AbstractArray, [dim...])
 
@@ -839,14 +850,6 @@ isempty(a::AbstractArray) = (_length(a) == 0)
 # keys with an IndexStyle
 keys(s::IndexStyle, A::AbstractArray, B::AbstractArray...) = eachindex(s, A, B...)
 
-## Conversions ##
-
-convert(::Type{AbstractArray{T,N}}, A::AbstractArray{T,N}) where {T,N  } = A
-convert(::Type{AbstractArray{T,N}}, A::AbstractArray{S,N}) where {T,S,N} = copy!(similar(A,T), A)
-convert(::Type{AbstractArray{T}},   A::AbstractArray{S,N}) where {T,S,N} = convert(AbstractArray{T,N}, A)
-
-convert(::Type{Array}, A::AbstractArray{T,N}) where {T,N} = convert(Array{T,N}, A)
-
 """
    of_indices(x, y)
 

base/array.jl

@@ -549,23 +549,14 @@ end
 one(x::AbstractMatrix{T}) where {T} = _one(one(T), x)
 oneunit(x::AbstractMatrix{T}) where {T} = _one(oneunit(T), x)
 
-## Conversions ##
-
-convert(::Type{Vector}, x::AbstractVector{T}) where {T} = convert(Vector{T}, x)
-convert(::Type{Matrix}, x::AbstractMatrix{T}) where {T} = convert(Matrix{T}, x)
-
-convert(::Type{Array{T}}, x::Array{T,n}) where {T,n} = x
-convert(::Type{Array{T,n}}, x::Array{T,n}) where {T,n} = x
-
-convert(::Type{Array{T}}, x::AbstractArray{S,n}) where {T,n,S} = convert(Array{T,n}, x)
-convert(::Type{Array{T,n}}, x::AbstractArray{S,n}) where {T,n,S} = copy!(Array{T,n}(size(x)), x)
-
 promote_rule(a::Type{Array{T,n}}, b::Type{Array{S,n}}) where {T,n,S} = el_same(promote_type(T,S), a, b)
 
-# constructors should make copies
+## Constructors ##
 
 if module_name(@__MODULE__) === :Base  # avoid method overwrite
-(::Type{T})(x::T) where {T<:Array} = copy(x)
+# constructors should make copies
+Array{T,N}(x::AbstractArray{S,N})         where {T,N,S} = copy!(Array{T,N}(size(x)), x)
+AbstractArray{T,N}(A::AbstractArray{S,N}) where {T,N,S} = copy!(similar(A,T), A)
 end
 
 ## copying iterators to containers

base/bitarray.jl

@@ -497,21 +497,19 @@ function _bitreshape(B::BitArray, dims::NTuple{N,Int}) where N
     return Br
 end
 
-## Conversions ##
+## Constructors ##
 
-convert(::Type{Array{T}}, B::BitArray{N}) where {T,N} = convert(Array{T,N}, B)
-convert(::Type{Array{T,N}}, B::BitArray{N}) where {T,N} = _convert(Array{T,N}, B) # see #15801
-function _convert(::Type{Array{T,N}}, B::BitArray{N}) where {T,N}
-    A = Array{T}(size(B))
+function Array{T,N}(B::BitArray{N}) where {T,N}
+    A = Array{T,N}(size(B))
     Bc = B.chunks
     @inbounds for i = 1:length(A)
         A[i] = unsafe_bitgetindex(Bc, i)
     end
     return A
 end
 
-convert(::Type{BitArray}, A::AbstractArray{T,N}) where {T,N} = convert(BitArray{N}, A)
-function convert(::Type{BitArray{N}}, A::AbstractArray{T,N}) where N where T
+BitArray(A::AbstractArray{<:Any,N}) where {N} = BitArray{N}(A)
+function BitArray{N}(A::AbstractArray{T,N}) where N where T
     B = BitArray(size(A))
     Bc = B.chunks
     l = length(B)
@@ -536,7 +534,7 @@ function convert(::Type{BitArray{N}}, A::AbstractArray{T,N}) where N where T
     return B
 end
 
-function convert(::Type{BitArray{N}}, A::Array{Bool,N}) where N
+function BitArray{N}(A::Array{Bool,N}) where N
     B = BitArray(size(A))
     Bc = B.chunks
     l = length(B)
@@ -545,16 +543,9 @@ function convert(::Type{BitArray{N}}, A::Array{Bool,N}) where N
     return B
 end
 
-convert(::Type{BitArray{N}}, B::BitArray{N}) where {N} = B
-convert(::Type{AbstractArray{T,N}}, B::BitArray{N}) where {T,N} = convert(Array{T,N}, B)
-
 reinterpret(::Type{Bool}, B::BitArray, dims::NTuple{N,Int}) where {N} = reinterpret(B, dims)
 reinterpret(B::BitArray, dims::NTuple{N,Int}) where {N} = reshape(B, dims)
 
-## Constructors from generic iterables ##
-
-BitArray(A::AbstractArray{<:Any,N}) where {N} = convert(BitArray{N}, A)
-
 if module_name(@__MODULE__) === :Base  # avoid method overwrite
 (::Type{T})(x::T) where {T<:BitArray} = copy(x)
 end

base/boot.jl

@@ -382,6 +382,13 @@ Array{T}(m::Int, n::Int, o::Int) where {T} = Array{T,3}(m, n, o)
 
 Array{T,1}() where {T} = Array{T,1}(0)
 
+(::Type{Array{T,N} where T})(x::AbstractArray{S,N}) where {S,N} = Array{S,N}(x)
+
+Array(A::AbstractArray{T,N})    where {T,N}   = Array{T,N}(A)
+Array{T}(A::AbstractArray{S,N}) where {T,N,S} = Array{T,N}(A)
+
+AbstractArray{T}(A::AbstractArray{S,N}) where {T,S,N} = AbstractArray{T,N}(A)
+
 # primitive Symbol constructors
 function Symbol(s::String)
     return ccall(:jl_symbol_n, Ref{Symbol}, (Ptr{UInt8}, Int),
@@ -602,6 +609,7 @@ UInt128(x::BuiltinInts) = toUInt128(x)::UInt128
 UInt32(x::Char) = bitcast(UInt32, x)
 Char(x::UInt32) = bitcast(Char, x)
 Char(x::Number) = Char(UInt32(x))
+Char(x::Char) = x
 (::Type{T})(x::Char) where {T<:Number} = T(UInt32(x))
 
 (::Type{T})(x::T) where {T<:Number} = x

base/dates/periods.jl

@@ -401,8 +401,13 @@ function divexact(x, y)
     return q
 end
 
+# TODO: this is needed to prevent undefined Period constructors from
+# hitting the deprecated construct-to-convert fallback.
+(::Type{T})(p::Period) where {T<:Period} = convert(T, p)::T
+
 # FixedPeriod conversions and promotion rules
-const fixedperiod_conversions = [(Week, 7), (Day, 24), (Hour, 60), (Minute, 60), (Second, 1000), (Millisecond, 1000), (Microsecond, 1000), (Nanosecond, 1)]
+const fixedperiod_conversions = [(:Week, 7), (:Day, 24), (:Hour, 60), (:Minute, 60), (:Second, 1000),
+                                 (:Millisecond, 1000), (:Microsecond, 1000), (:Nanosecond, 1)]
 for i = 1:length(fixedperiod_conversions)
     T, n = fixedperiod_conversions[i]
     N = Int64(1)

base/deprecated.jl

@@ -1697,6 +1697,21 @@ export hex2num
 
 @deprecate convert(dt::Type{<:Integer}, ip::IPAddr)  dt(ip)
 
+function (::Type{T})(arg) where {T}
+    if applicable(convert, T, arg)
+        sig = which(convert, (Type{T}, typeof(arg))).sig
+        if sig == (Tuple{typeof(convert),Type{S},Number} where S<:Number) ||
+           sig == (Tuple{typeof(convert),Type{S},AbstractArray} where S<:AbstractArray)
+            # matches a catch-all converter; will stack overflow
+            throw(MethodError(T, (arg,)))
+        end
+        # if `convert` call would not work, just let the method error happen
+        depwarn("Constructors no longer fall back to `convert`. A constructor `$T(::$(typeof(arg)))` should be defined instead.", :Type)
+    end
+    convert(T, arg)::T
+end
+# related items to remove in: abstractarray.jl, dates/periods.jl
+
 # Issue #19923
 @deprecate ror                  circshift
 @deprecate ror!                 circshift!

base/libgit2/types.jl

@@ -20,6 +20,7 @@ struct GitHash <: AbstractGitHash
     GitHash(val::NTuple{OID_RAWSZ, UInt8}) = new(val)
 end
 GitHash() = GitHash(ntuple(i->zero(UInt8), OID_RAWSZ))
+GitHash(h::GitHash) = h
 
 """
     GitShortHash(hash::GitHash, len::Integer)

base/linalg/bidiag.jl

@@ -93,6 +93,8 @@ function Bidiagonal(A::AbstractMatrix, uplo::Symbol)
     Bidiagonal(diag(A, 0), diag(A, uplo == :U ? 1 : -1), uplo)
 end
 
+Bidiagonal(A::Bidiagonal) = A
+
 function getindex(A::Bidiagonal{T}, i::Integer, j::Integer) where T
     if !((1 <= i <= size(A,2)) && (1 <= j <= size(A,2)))
         throw(BoundsError(A,(i,j)))
@@ -131,7 +133,7 @@ function Base.replace_in_print_matrix(A::Bidiagonal,i::Integer,j::Integer,s::Abs
 end
 
 #Converting from Bidiagonal to dense Matrix
-function convert(::Type{Matrix{T}}, A::Bidiagonal) where T
+function Matrix{T}(A::Bidiagonal) where T
     n = size(A, 1)
     B = zeros(T, n, n)
     for i = 1:n - 1
@@ -145,14 +147,14 @@ function convert(::Type{Matrix{T}}, A::Bidiagonal) where T
     B[n,n] = A.dv[n]
     return B
 end
-convert(::Type{Matrix}, A::Bidiagonal{T}) where {T} = convert(Matrix{T}, A)
-convert(::Type{Array}, A::Bidiagonal) = convert(Matrix, A)
-full(A::Bidiagonal) = convert(Array, A)
+Matrix(A::Bidiagonal{T}) where {T} = Matrix{T}(A)
+Array(A::Bidiagonal) = Matrix(A)
+full(A::Bidiagonal) = Array(A)
 promote_rule(::Type{Matrix{T}}, ::Type{<:Bidiagonal{S}}) where {T,S} = Matrix{promote_type(T,S)}
 
 #Converting from Bidiagonal to Tridiagonal
-Tridiagonal(M::Bidiagonal{T}) where {T} = convert(Tridiagonal{T}, M)
-function convert(::Type{Tridiagonal{T}}, A::Bidiagonal) where T
+Tridiagonal(M::Bidiagonal{T}) where {T} = Tridiagonal{T}(M)
+function Tridiagonal{T}(A::Bidiagonal) where T
     dv = convert(AbstractVector{T}, A.dv)
     ev = convert(AbstractVector{T}, A.ev)
     z = fill!(similar(ev), zero(T))
@@ -161,12 +163,12 @@ end
 promote_rule(::Type{<:Tridiagonal{T}}, ::Type{<:Bidiagonal{S}}) where {T,S} = Tridiagonal{promote_type(T,S)}
 
 # No-op for trivial conversion Bidiagonal{T} -> Bidiagonal{T}
-convert(::Type{Bidiagonal{T}}, A::Bidiagonal{T}) where {T} = A
+Bidiagonal{T}(A::Bidiagonal{T}) where {T} = A
 # Convert Bidiagonal to Bidiagonal{T} by constructing a new instance with converted elements
-convert(::Type{Bidiagonal{T}}, A::Bidiagonal) where {T} =
+Bidiagonal{T}(A::Bidiagonal) where {T} =
     Bidiagonal(convert(AbstractVector{T}, A.dv), convert(AbstractVector{T}, A.ev), A.uplo)
 # When asked to convert Bidiagonal to AbstractMatrix{T}, preserve structure by converting to Bidiagonal{T} <: AbstractMatrix{T}
-convert(::Type{AbstractMatrix{T}}, A::Bidiagonal) where {T} = convert(Bidiagonal{T}, A)
+AbstractMatrix{T}(A::Bidiagonal) where {T} = convert(Bidiagonal{T}, A)
 
 broadcast(::typeof(big), B::Bidiagonal) = Bidiagonal(big.(B.dv), big.(B.ev), B.uplo)
 

base/linalg/cholesky.jl

@@ -347,32 +347,32 @@ function cholfact(x::Number, uplo::Symbol=:U)
 end
 
 
-function convert(::Type{Cholesky{T}}, C::Cholesky) where T
+function Cholesky{T}(C::Cholesky) where T
     Cnew = convert(AbstractMatrix{T}, C.factors)
     Cholesky{T, typeof(Cnew)}(Cnew, C.uplo, C.info)
 end
-convert(::Type{Factorization{T}}, C::Cholesky{T}) where {T} = C
-convert(::Type{Factorization{T}}, C::Cholesky) where {T} = convert(Cholesky{T}, C)
-convert(::Type{CholeskyPivoted{T}},C::CholeskyPivoted{T}) where {T} = C
-convert(::Type{CholeskyPivoted{T}},C::CholeskyPivoted) where {T} =
+Factorization{T}(C::Cholesky{T}) where {T} = C
+Factorization{T}(C::Cholesky) where {T} = Cholesky{T}(C)
+CholeskyPivoted{T}(C::CholeskyPivoted{T}) where {T} = C
+CholeskyPivoted{T}(C::CholeskyPivoted) where {T} =
     CholeskyPivoted(AbstractMatrix{T}(C.factors),C.uplo,C.piv,C.rank,C.tol,C.info)
-convert(::Type{Factorization{T}}, C::CholeskyPivoted{T}) where {T} = C
-convert(::Type{Factorization{T}}, C::CholeskyPivoted) where {T} = convert(CholeskyPivoted{T}, C)
+Factorization{T}(C::CholeskyPivoted{T}) where {T} = C
+Factorization{T}(C::CholeskyPivoted) where {T} = CholeskyPivoted{T}(C)
 
-convert(::Type{AbstractMatrix}, C::Cholesky) = C.uplo == 'U' ? C[:U]'C[:U] : C[:L]*C[:L]'
-convert(::Type{AbstractArray}, C::Cholesky) = convert(AbstractMatrix, C)
-convert(::Type{Matrix}, C::Cholesky) = convert(Array, convert(AbstractArray, C))
-convert(::Type{Array}, C::Cholesky) = convert(Matrix, C)
-full(C::Cholesky) = convert(AbstractArray, C)
+AbstractMatrix(C::Cholesky) = C.uplo == 'U' ? C[:U]'C[:U] : C[:L]*C[:L]'
+AbstractArray(C::Cholesky) = AbstractMatrix(C)
+Matrix(C::Cholesky) = Array(AbstractArray(C))
+Array(C::Cholesky) = Matrix(C)
+full(C::Cholesky) = AbstractArray(C)
 
-function convert(::Type{AbstractMatrix}, F::CholeskyPivoted)
+function AbstractMatrix(F::CholeskyPivoted)
     ip = invperm(F[:p])
     (F[:L] * F[:U])[ip,ip]
 end
-convert(::Type{AbstractArray}, F::CholeskyPivoted) = convert(AbstractMatrix, F)
-convert(::Type{Matrix}, F::CholeskyPivoted) = convert(Array, convert(AbstractArray, F))
-convert(::Type{Array}, F::CholeskyPivoted) = convert(Matrix, F)
-full(F::CholeskyPivoted) = convert(AbstractArray, F)
+AbstractArray(F::CholeskyPivoted) = AbstractMatrix(F)
+Matrix(F::CholeskyPivoted) = Array(AbstractArray(F))
+Array(F::CholeskyPivoted) = Matrix(F)
+full(F::CholeskyPivoted) = AbstractArray(F)
 
 copy(C::Cholesky) = Cholesky(copy(C.factors), C.uplo, C.info)
 copy(C::CholeskyPivoted) = CholeskyPivoted(copy(C.factors), C.uplo, C.piv, C.rank, C.tol, C.info)