Force inference of convert(::Type{T}, ::T) where T via typeasserts

base/Enums.jl

@@ -17,7 +17,7 @@ abstract type Enum{T<:Integer} end
 basetype(::Type{<:Enum{T}}) where {T<:Integer} = T
 
 (::Type{T})(x::Enum{T2}) where {T<:Integer,T2<:Integer} = T(bitcast(T2, x))::T
-Base.cconvert(::Type{T}, x::Enum{T2}) where {T<:Integer,T2<:Integer} = T(x)
+Base.cconvert(::Type{T}, x::Enum{T2}) where {T<:Integer,T2<:Integer} = T(x)::T
 Base.write(io::IO, x::Enum{T}) where {T<:Integer} = write(io, T(x))
 Base.read(io::IO, ::Type{T}) where {T<:Enum} = T(read(io, basetype(T)))
 

base/abstractarray.jl

@@ -14,8 +14,8 @@ See also: [`AbstractVector`](@ref), [`AbstractMatrix`](@ref), [`eltype`](@ref),
 AbstractArray
 
 convert(::Type{T}, a::T) where {T<:AbstractArray} = 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)
+convert(::Type{AbstractArray{T}}, a::AbstractArray) where {T} = AbstractArray{T}(a)::AbstractArray{T}
+convert(::Type{AbstractArray{T,N}}, a::AbstractArray{<:Any,N}) where {T,N} = AbstractArray{T,N}(a)::AbstractArray{T,N}
 
 """
     size(A::AbstractArray, [dim])

base/abstractdict.jl

@@ -565,7 +565,7 @@ push!(t::AbstractDict, p::Pair, q::Pair, r::Pair...) = push!(push!(push!(t, p),
 convert(::Type{T}, x::T) where {T<:AbstractDict} = x
 
 function convert(::Type{T}, x::AbstractDict) where T<:AbstractDict
-    h = T(x)
+    h = T(x)::T
     if length(h) != length(x)
         error("key collision during dictionary conversion")
     end

base/array.jl

@@ -610,7 +610,7 @@ oneunit(x::AbstractMatrix{T}) where {T} = _one(oneunit(T), x)
 
 ## Conversions ##
 
-convert(::Type{T}, a::AbstractArray) where {T<:Array} = a isa T ? a : T(a)
+convert(::Type{T}, a::AbstractArray) where {T<:Array} = a isa T ? a : T(a)::T
 
 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/baseext.jl

@@ -16,7 +16,7 @@ VecElement
 # hook up VecElement constructor to Base.convert
 VecElement{T}(arg) where {T} = VecElement{T}(convert(T, arg))
 convert(::Type{T}, arg::T) where {T<:VecElement} = arg
-convert(::Type{T}, arg)  where {T<:VecElement} = T(arg)
+convert(::Type{T}, arg)  where {T<:VecElement} = T(arg)::T
 
 # ## dims-type-converting Array constructors for convenience
 # type and dimensionality specified, accepting dims as series of Integers

base/bitarray.jl

@@ -577,7 +577,7 @@ julia> BitArray(x+y == 3 for x = 1:2 for y = 1:3)
 BitArray(itr) = gen_bitarray(IteratorSize(itr), itr)
 BitArray{N}(itr) where N = gen_bitarrayN(BitArray{N}, IteratorSize(itr), itr)
 
-convert(T::Type{<:BitArray}, a::AbstractArray) = a isa T ? a : T(a)
+convert(::Type{T}, a::AbstractArray) where {T<:BitArray} = a isa T ? a : T(a)::T
 
 # generic constructor from an iterable without compile-time info
 # (we pass start(itr) explicitly to avoid a type-instability with filters)

base/broadcast.jl

@@ -195,7 +195,7 @@ function broadcasted(::OrOr, a, bc::Broadcasted)
 end
 
 Base.convert(::Type{Broadcasted{NewStyle}}, bc::Broadcasted{Style,Axes,F,Args}) where {NewStyle,Style,Axes,F,Args} =
-    Broadcasted{NewStyle,Axes,F,Args}(bc.f, bc.args, bc.axes)
+    Broadcasted{NewStyle,Axes,F,Args}(bc.f, bc.args, bc.axes)::Broadcasted{NewStyle,Axes,F,Args}
 
 function Base.show(io::IO, bc::Broadcasted{Style}) where {Style}
     print(io, Broadcasted)

base/char.jl

@@ -181,9 +181,9 @@ end
 end
 
 convert(::Type{AbstractChar}, x::Number) = Char(x) # default to Char
-convert(::Type{T}, x::Number) where {T<:AbstractChar} = T(x)
-convert(::Type{T}, x::AbstractChar) where {T<:Number} = T(x)
-convert(::Type{T}, c::AbstractChar) where {T<:AbstractChar} = T(c)
+convert(::Type{T}, x::Number) where {T<:AbstractChar} = T(x)::T
+convert(::Type{T}, x::AbstractChar) where {T<:Number} = T(x)::T
+convert(::Type{T}, c::AbstractChar) where {T<:AbstractChar} = T(c)::T
 convert(::Type{T}, c::T) where {T<:AbstractChar} = c
 
 rem(x::AbstractChar, ::Type{T}) where {T<:Number} = rem(codepoint(x), T)

base/indices.jl

@@ -476,7 +476,7 @@ struct LinearIndices{N,R<:NTuple{N,AbstractUnitRange{Int}}} <: AbstractArray{Int
     indices::R
 end
 convert(::Type{LinearIndices{N,R}}, inds::LinearIndices{N}) where {N,R<:NTuple{N,AbstractUnitRange{Int}}} =
-    LinearIndices{N,R}(convert(R, inds.indices))
+    LinearIndices{N,R}(convert(R, inds.indices))::LinearIndices{N,R}
 
 LinearIndices(::Tuple{}) = LinearIndices{0,typeof(())}(())
 LinearIndices(inds::NTuple{N,AbstractUnitRange{<:Integer}}) where {N} =

base/multidimensional.jl

@@ -325,7 +325,7 @@ module IteratorsMD
         convert(Tuple{Vararg{UnitRange{Int}}}, R)
 
     convert(::Type{CartesianIndices{N,R}}, inds::CartesianIndices{N}) where {N,R} =
-        CartesianIndices(convert(R, inds.indices))
+        CartesianIndices(convert(R, inds.indices))::CartesianIndices{N,R}
 
     # equality
     Base.:(==)(a::CartesianIndices{N}, b::CartesianIndices{N}) where N =

base/namedtuple.jl

@@ -148,7 +148,7 @@ convert(::Type{NamedTuple{names,T}}, nt::NamedTuple{names,T}) where {names,T<:Tu
 convert(::Type{NamedTuple{names}}, nt::NamedTuple{names}) where {names} = nt
 
 function convert(::Type{NamedTuple{names,T}}, nt::NamedTuple{names}) where {names,T<:Tuple}
-    NamedTuple{names,T}(T(nt))
+    NamedTuple{names,T}(T(nt))::NamedTuple{names,T}
 end
 
 if nameof(@__MODULE__) === :Base

base/number.jl

@@ -4,7 +4,7 @@
 
 # Numbers are convertible
 convert(::Type{T}, x::T)      where {T<:Number} = x
-convert(::Type{T}, x::Number) where {T<:Number} = T(x)
+convert(::Type{T}, x::Number) where {T<:Number} = T(x)::T
 
 """
     isinteger(x) -> Bool

base/pair.jl

@@ -55,7 +55,7 @@ last(p::Pair) = p.second
 
 convert(::Type{Pair{A,B}}, x::Pair{A,B}) where {A,B} = x
 function convert(::Type{Pair{A,B}}, x::Pair) where {A,B}
-    Pair{A,B}(convert(A, x[1]), convert(B, x[2]))
+    Pair{A,B}(convert(A, x[1]), convert(B, x[2]))::Pair{A,B}
 end
 
 promote_rule(::Type{Pair{A1,B1}}, ::Type{Pair{A2,B2}}) where {A1,B1,A2,B2} =

base/pointer.jl

@@ -20,14 +20,14 @@ const C_NULL = bitcast(Ptr{Cvoid}, 0)
 # TODO: deprecate these conversions. C doesn't even allow them.
 
 # pointer to integer
-convert(::Type{T}, x::Ptr) where {T<:Integer} = T(UInt(x))
+convert(::Type{T}, x::Ptr) where {T<:Integer} = T(UInt(x))::T
 
 # integer to pointer
 convert(::Type{Ptr{T}}, x::Union{Int,UInt}) where {T} = Ptr{T}(x)
 
 # pointer to pointer
 convert(::Type{Ptr{T}}, p::Ptr{T}) where {T} = p
-convert(::Type{Ptr{T}}, p::Ptr) where {T} = bitcast(Ptr{T}, p)
+convert(::Type{Ptr{T}}, p::Ptr) where {T} = bitcast(Ptr{T}, p)::Ptr{T}
 
 # object to pointer (when used with ccall)
 

base/range.jl

@@ -252,7 +252,7 @@ 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)
+convert(::Type{T}, r::AbstractRange) where {T<:AbstractRange} = r isa T ? r : T(r)::T
 
 ## ordinal ranges
 

base/refpointer.jl

@@ -101,7 +101,7 @@ IteratorSize(::Type{<:Ref}) = HasShape{0}()
 unsafe_convert(::Type{Ref{T}}, x::Ref{T}) where {T} = unsafe_convert(Ptr{T}, x)
 unsafe_convert(::Type{Ref{T}}, x) where {T} = unsafe_convert(Ptr{T}, x)
 
-convert(::Type{Ref{T}}, x) where {T} = RefValue{T}(x)
+convert(::Type{Ref{T}}, x) where {T} = RefValue{T}(x)::RefValue{T}
 
 ### Methods for a Ref object that is backed by an array at index i
 struct RefArray{T,A<:AbstractArray{T},R} <: Ref{T}

base/set.jl

@@ -548,7 +548,7 @@ function hash(s::AbstractSet, h::UInt)
 end
 
 convert(::Type{T}, s::T) where {T<:AbstractSet} = s
-convert(::Type{T}, s::AbstractSet) where {T<:AbstractSet} = T(s)
+convert(::Type{T}, s::AbstractSet) where {T<:AbstractSet} = T(s)::T
 
 
 ## replace/replace! ##

base/show.jl

@@ -303,7 +303,7 @@ function IOContext(io::IO, dict::ImmutableDict)
     IOContext{typeof(io0)}(io0, dict)
 end
 
-convert(::Type{IOContext}, io::IO) = IOContext(unwrapcontext(io)...)
+convert(::Type{IOContext}, io::IO) = IOContext(unwrapcontext(io)...)::IOContext
 
 IOContext(io::IO) = convert(IOContext, io)
 

base/some.jl

@@ -35,7 +35,7 @@ end
 convert(::Type{T}, x::T) where {T>:Nothing} = x
 convert(::Type{T}, x) where {T>:Nothing} = convert(nonnothingtype_checked(T), x)
 convert(::Type{Some{T}}, x::Some{T}) where {T} = x
-convert(::Type{Some{T}}, x::Some) where {T} = Some{T}(convert(T, x.value))
+convert(::Type{Some{T}}, x::Some) where {T} = Some{T}(convert(T, x.value))::Some{T}
 
 function show(io::IO, x::Some)
     if get(io, :typeinfo, Any) == typeof(x)

base/strings/basic.jl

@@ -229,7 +229,7 @@ Symbol(s::AbstractString) = Symbol(String(s))
 Symbol(x...) = Symbol(string(x...))
 
 convert(::Type{T}, s::T) where {T<:AbstractString} = s
-convert(::Type{T}, s::AbstractString) where {T<:AbstractString} = T(s)
+convert(::Type{T}, s::AbstractString) where {T<:AbstractString} = T(s)::T
 
 ## summary ##
 

base/strings/substring.jl

@@ -55,13 +55,13 @@ SubString{T}(s::T) where {T<:AbstractString} = SubString{T}(s, 1, lastindex(s)::
 @propagate_inbounds maybeview(s::AbstractString, args...) = getindex(s, args...)
 
 convert(::Type{SubString{S}}, s::AbstractString) where {S<:AbstractString} =
-    SubString(convert(S, s))
+    SubString(convert(S, s))::SubString{S}
 convert(::Type{T}, s::T) where {T<:SubString} = s
 
 # Regex match allows only Union{String, SubString{String}} so define conversion to this type
 convert(::Type{Union{String, SubString{String}}}, s::String) = s
 convert(::Type{Union{String, SubString{String}}}, s::SubString{String}) = s
-convert(::Type{Union{String, SubString{String}}}, s::AbstractString) = convert(String, s)
+convert(::Type{Union{String, SubString{String}}}, s::AbstractString) = convert(String, s)::String
 
 function String(s::SubString{String})
     parent = s.string

base/twiceprecision.jl

@@ -268,10 +268,10 @@ TwicePrecision{T}(x::Number) where {T} = TwicePrecision{T}(T(x), zero(T))
 
 convert(::Type{TwicePrecision{T}}, x::TwicePrecision{T}) where {T} = x
 convert(::Type{TwicePrecision{T}}, x::TwicePrecision) where {T} =
-    TwicePrecision{T}(convert(T, x.hi), convert(T, x.lo))
+    TwicePrecision{T}(convert(T, x.hi), convert(T, x.lo))::TwicePrecision{T}
 
-convert(::Type{T}, x::TwicePrecision) where {T<:Number} = T(x)
-convert(::Type{TwicePrecision{T}}, x::Number) where {T} = TwicePrecision{T}(x)
+convert(::Type{T}, x::TwicePrecision) where {T<:Number} = T(x)::T
+convert(::Type{TwicePrecision{T}}, x::Number) where {T} = TwicePrecision{T}(x)::TwicePrecision{T}
 
 float(x::TwicePrecision{<:AbstractFloat}) = x
 float(x::TwicePrecision) = TwicePrecision(float(x.hi), float(x.lo))

doc/src/manual/conversion-and-promotion.md

@@ -181,7 +181,7 @@ For example, this definition states that it's valid to `convert` any `Number` ty
 any other by calling a 1-argument constructor:
 
 ```julia
-convert(::Type{T}, x::Number) where {T<:Number} = T(x)
+convert(::Type{T}, x::Number) where {T<:Number} = T(x)::T
 ```
 
 This means that new `Number` types only need to define constructors, since this

stdlib/Dates/test/periods.jl

@@ -283,7 +283,7 @@ Beat(p::Period) = Beat(Dates.toms(p) ÷ 86400)
     Dates.toms(b::Beat) = Dates.value(b) * 86400
     Dates._units(b::Beat) = " beat" * (abs(Dates.value(b)) == 1 ? "" : "s")
     Base.promote_rule(::Type{Dates.Day}, ::Type{Beat}) = Dates.Millisecond
-    Base.convert(::Type{T}, b::Beat) where {T<:Dates.Millisecond} = T(Dates.toms(b))
+    Base.convert(::Type{T}, b::Beat) where {T<:Dates.Millisecond} = T(Dates.toms(b))::T
 
     @test Beat(1000) == Dates.Day(1)
     @test Beat(1) < Dates.Day(1)

stdlib/LinearAlgebra/src/adjtrans.jl

@@ -308,8 +308,8 @@ IndexStyle(::Type{<:AdjOrTransAbsMat}) = IndexCartesian()
 @propagate_inbounds getindex(v::AdjOrTransAbsVec, ::Colon, ::Colon) = wrapperop(v)(v.parent[:])
 
 # conversion of underlying storage
-convert(::Type{Adjoint{T,S}}, A::Adjoint) where {T,S} = Adjoint{T,S}(convert(S, A.parent))
-convert(::Type{Transpose{T,S}}, A::Transpose) where {T,S} = Transpose{T,S}(convert(S, A.parent))
+convert(::Type{Adjoint{T,S}}, A::Adjoint) where {T,S} = Adjoint{T,S}(convert(S, A.parent))::Adjoint{T,S}
+convert(::Type{Transpose{T,S}}, A::Transpose) where {T,S} = Transpose{T,S}(convert(S, A.parent))::Transpose{T,S}
 
 # Strides and pointer for transposed strided arrays — but only if the elements are actually stored in memory
 Base.strides(A::Adjoint{<:Real, <:AbstractVector}) = (stride(A.parent, 2), stride(A.parent, 1))

stdlib/LinearAlgebra/src/bidiag.jl

@@ -200,7 +200,7 @@ promote_rule(::Type{<:Tridiagonal}, ::Type{<:Bidiagonal}) = Tridiagonal
 # 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)
+convert(::Type{T}, m::AbstractMatrix) where {T<:Bidiagonal} = m isa T ? m : T(m)::T
 
 similar(B::Bidiagonal, ::Type{T}) where {T} = Bidiagonal(similar(B.dv, T), similar(B.ev, T), B.uplo)
 similar(B::Bidiagonal, ::Type{T}, dims::Union{Dims{1},Dims{2}}) where {T} = zeros(T, dims...)

stdlib/LinearAlgebra/src/factorization.jl

@@ -54,9 +54,9 @@ function det(F::Factorization)
 end
 
 convert(::Type{T}, f::T) where {T<:Factorization} = f
-convert(::Type{T}, f::Factorization) where {T<:Factorization} = T(f)
+convert(::Type{T}, f::Factorization) where {T<:Factorization} = T(f)::T
 
-convert(::Type{T}, f::Factorization) where {T<:AbstractArray} = T(f)
+convert(::Type{T}, f::Factorization) where {T<:AbstractArray} = T(f)::T
 
 ### General promotion rules
 Factorization{T}(F::Factorization{T}) where {T} = F

stdlib/LinearAlgebra/src/givens.jl

@@ -44,7 +44,7 @@ struct Rotation{T} <: AbstractRotation{T}
 end
 
 convert(::Type{T}, r::T) where {T<:AbstractRotation} = r
-convert(::Type{T}, r::AbstractRotation) where {T<:AbstractRotation} = T(r)
+convert(::Type{T}, r::AbstractRotation) where {T<:AbstractRotation} = T(r)::T
 
 Givens(i1, i2, c, s) = Givens(i1, i2, promote(c, s)...)
 Givens{T}(G::Givens{T}) where {T} = G

stdlib/LinearAlgebra/src/special.jl

@@ -62,20 +62,20 @@ end
 const ConvertibleSpecialMatrix = Union{Diagonal,Bidiagonal,SymTridiagonal,Tridiagonal,AbstractTriangular}
 const PossibleTriangularMatrix = Union{Diagonal, Bidiagonal, AbstractTriangular}
 
-convert(T::Type{<:Diagonal},       m::ConvertibleSpecialMatrix) = m isa T ? m :
-    isdiag(m) ? T(m) : throw(ArgumentError("matrix cannot be represented as Diagonal"))
-convert(T::Type{<:SymTridiagonal}, m::ConvertibleSpecialMatrix) = m isa T ? m :
-    issymmetric(m) && isbanded(m, -1, 1) ? T(m) : throw(ArgumentError("matrix cannot be represented as SymTridiagonal"))
-convert(T::Type{<:Tridiagonal},    m::ConvertibleSpecialMatrix) = m isa T ? m :
-    isbanded(m, -1, 1) ? T(m) : throw(ArgumentError("matrix cannot be represented as Tridiagonal"))
-
-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)
-
-convert(T::Type{<:LowerTriangular}, m::PossibleTriangularMatrix) = m isa T ? m :
-    istril(m) ? T(m) : throw(ArgumentError("matrix cannot be represented as LowerTriangular"))
-convert(T::Type{<:UpperTriangular}, m::PossibleTriangularMatrix) = m isa T ? m :
-    istriu(m) ? T(m) : throw(ArgumentError("matrix cannot be represented as UpperTriangular"))
+convert(::Type{T}, m::ConvertibleSpecialMatrix) where {T<:Diagonal}       = m isa T ? m :
+    isdiag(m) ? T(m)::T : throw(ArgumentError("matrix cannot be represented as Diagonal"))
+convert(::Type{T}, m::ConvertibleSpecialMatrix) where {T<:SymTridiagonal} = m isa T ? m :
+    issymmetric(m) && isbanded(m, -1, 1) ? T(m)::T : throw(ArgumentError("matrix cannot be represented as SymTridiagonal"))
+convert(::Type{T}, m::ConvertibleSpecialMatrix) where {T<:Tridiagonal}    = m isa T ? m :
+    isbanded(m, -1, 1) ? T(m)::T : throw(ArgumentError("matrix cannot be represented as Tridiagonal"))
+
+convert(::Type{T}, m::Union{LowerTriangular,UnitLowerTriangular}) where {T<:LowerTriangular} = m isa T ? m : T(m)::T
+convert(::Type{T}, m::Union{UpperTriangular,UnitUpperTriangular}) where {T<:UpperTriangular} = m isa T ? m : T(m)::T
+
+convert(::Type{T}, m::PossibleTriangularMatrix) where {T<:LowerTriangular} = m isa T ? m :
+    istril(m) ? T(m)::T : throw(ArgumentError("matrix cannot be represented as LowerTriangular"))
+convert(::Type{T}, m::PossibleTriangularMatrix) where {T<:UpperTriangular} = m isa T ? m :
+    istriu(m) ? T(m)::T : throw(ArgumentError("matrix cannot be represented as UpperTriangular"))
 
 # 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

stdlib/LinearAlgebra/src/symmetric.jl

@@ -192,8 +192,8 @@ 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)
+convert(::Type{T}, m::Union{Symmetric,Hermitian}) where {T<:Symmetric} = m isa T ? m : T(m)::T
+convert(::Type{T}, m::Union{Symmetric,Hermitian}) where {T<:Hermitian} = m isa T ? m : T(m)::T
 
 const HermOrSym{T,        S} = Union{Hermitian{T,S}, Symmetric{T,S}}
 const RealHermSym{T<:Real,S} = Union{Hermitian{T,S}, Symmetric{T,S}}

stdlib/LinearAlgebra/src/uniformscaling.jl

@@ -118,7 +118,7 @@ function show(io::IO, ::MIME"text/plain", J::UniformScaling)
 end
 copy(J::UniformScaling) = UniformScaling(J.λ)
 
-Base.convert(::Type{UniformScaling{T}}, J::UniformScaling) where {T} = UniformScaling(convert(T, J.λ))
+Base.convert(::Type{UniformScaling{T}}, J::UniformScaling) where {T} = UniformScaling(convert(T, J.λ))::UniformScaling{T}
 
 conj(J::UniformScaling) = UniformScaling(conj(J.λ))
 real(J::UniformScaling) = UniformScaling(real(J.λ))

stdlib/SharedArrays/src/SharedArrays.jl

@@ -374,7 +374,7 @@ function SharedArray{TS,N}(A::Array{TA,N}) where {TS,TA,N}
     copyto!(S, A)
 end
 
-convert(T::Type{<:SharedArray}, a::Array) = T(a)
+convert(T::Type{<:SharedArray}, a::Array) = T(a)::T
 
 function deepcopy_internal(S::SharedArray, stackdict::IdDict)
     haskey(stackdict, S) && return stackdict[S]

test/testhelpers/Furlongs.jl

@@ -25,15 +25,15 @@ Base.promote_type(::Type{Furlong{p,T}}, ::Type{Furlong{p,S}}) where {p,T,S} =
     Furlong{p,promote_type(T,S)}
 
 # only Furlong{0} forms a ring and isa Number
-Base.convert(::Type{T}, y::Number) where {T<:Furlong{0}} = T(y)
+Base.convert(::Type{T}, y::Number) where {T<:Furlong{0}} = T(y)::T
 Base.convert(::Type{Furlong}, y::Number) = Furlong{0}(y)
 Base.convert(::Type{Furlong{<:Any,T}}, y::Number) where {T<:Number} = Furlong{0,T}(y)
 Base.convert(::Type{T}, y::Number) where {T<:Furlong} = typeassert(y, T) # throws, since cannot convert a Furlong{0} to a Furlong{p}
 # other Furlong{p} form a group
-Base.convert(::Type{T}, y::Furlong) where {T<:Furlong{0}} = T(y)
+Base.convert(::Type{T}, y::Furlong) where {T<:Furlong{0}} = T(y)::T
 Base.convert(::Type{Furlong}, y::Furlong) = y
 Base.convert(::Type{Furlong{<:Any,T}}, y::Furlong{p}) where {p,T<:Number} = Furlong{p,T}(y)
-Base.convert(::Type{T}, y::Furlong) where {T<:Furlong} = T(y)
+Base.convert(::Type{T}, y::Furlong) where {T<:Furlong} = T(y)::T
 
 Base.one(x::Furlong{p,T}) where {p,T} = one(T)
 Base.one(::Type{Furlong{p,T}}) where {p,T} = one(T)