RFC: promote ranges to the largest of the the start, step, or length (as applicable)

base/broadcast.jl

@@ -1130,6 +1130,7 @@ broadcasted(::DefaultArrayStyle{1}, ::typeof(*), r::LinRange, x::Number) = LinRa
 broadcasted(::DefaultArrayStyle{1}, ::typeof(*), r::OrdinalRange, x::AbstractFloat) =
     Base.range_start_step_length(first(r)*x, step(r)*x, length(r))
 
+#broadcasted(::DefaultArrayStyle{1}, ::typeof(/), r::AbstractRange, x::Number) = range(first(r)/x, last(r)/x, length=length(r))
 broadcasted(::DefaultArrayStyle{1}, ::typeof(/), r::AbstractRange, x::Number) = range(first(r)/x, step=step(r)/x, length=length(r))
 broadcasted(::DefaultArrayStyle{1}, ::typeof(/), r::StepRangeLen{T}, x::Number) where {T} =
     StepRangeLen{typeof(T(r.ref)/x)}(r.ref/x, r.step/x, length(r), r.offset)

base/math.jl

@@ -682,7 +682,7 @@ function _hypot(x, y)
 
     # Return Inf if either or both inputs is Inf (Compliance with IEEE754)
     if isinf(ax) || isinf(ay)
-        return oftype(axu, Inf)
+        return typeof(axu)(Inf)
     end
 
     # Order the operands
@@ -745,7 +745,7 @@ _hypot(x::ComplexF16, y::ComplexF16) = Float16(_hypot(ComplexF32(x), ComplexF32(
 function _hypot(x...)
     maxabs = maximum(abs, x)
     if isnan(maxabs) && any(isinf, x)
-        return oftype(maxabs, Inf)
+        return typeof(maxabs)(Inf)
     elseif (iszero(maxabs) || isinf(maxabs))
         return maxabs
     else

base/range.jl

@@ -1,21 +1,21 @@
 # This file is a part of Julia. License is MIT: https://julialang.org/license
 
-(:)(a::Real, b::Real) = (:)(promote(a,b)...)
+(:)(a::Real, b::Real) = (:)(promote(a, b)...)
 
 (:)(start::T, stop::T) where {T<:Real} = UnitRange{T}(start, stop)
 
 (:)(start::T, stop::T) where {T} = (:)(start, oftype(stop >= start ? stop - start : start - stop, 1), stop)
 
 # promote start and stop, leaving step alone
-(:)(start::A, step, stop::C) where {A<:Real,C<:Real} =
-    (:)(convert(promote_type(A,C),start), step, convert(promote_type(A,C),stop))
+(:)(start::A, step, stop::C) where {A<:Real, C<:Real} =
+    (:)(convert(promote_type(A, C), start), step, convert(promote_type(A, C), stop))
 
 # AbstractFloat specializations
 (:)(a::T, b::T) where {T<:AbstractFloat} = (:)(a, T(1), b)
 
-(:)(a::T, b::AbstractFloat, c::T) where {T<:Real} = (:)(promote(a,b,c)...)
-(:)(a::T, b::AbstractFloat, c::T) where {T<:AbstractFloat} = (:)(promote(a,b,c)...)
-(:)(a::T, b::Real, c::T) where {T<:AbstractFloat} = (:)(promote(a,b,c)...)
+(:)(a::T, b::AbstractFloat, c::T) where {T<:Real} = (:)(promote(a, b, c)...)
+(:)(a::T, b::AbstractFloat, c::T) where {T<:AbstractFloat} = (:)(promote(a, b, c)...)
+(:)(a::T, b::Real, c::T) where {T<:AbstractFloat} = (:)(promote(a, b, c)...)
 
 (:)(start::T, step::T, stop::T) where {T<:AbstractFloat} =
     _colon(OrderStyle(T), ArithmeticStyle(T), start, step, stop)
@@ -167,49 +167,39 @@ range_length(len::Integer) = OneTo(len)
 range_stop(stop) = range_start_stop(oftype(stop, 1), stop)
 range_stop(stop::Integer) = range_length(stop)
 
-# Stop and length as the only argument
-range_stop_length(a::Real,          len::Integer) = UnitRange{typeof(a)}(oftype(a, a-len+1), a)
-range_stop_length(a::AbstractFloat, len::Integer) = range_step_stop_length(oftype(a, 1), a, len)
-range_stop_length(a,                len::Integer) = range_step_stop_length(oftype(a-a, 1), a, len)
-
 range_step_stop_length(step, stop, length) = reverse(range_start_step_length(stop, -step, length))
 
-range_start_length(a::Real,          len::Integer) = UnitRange{typeof(a)}(a, oftype(a, a+len-1))
-range_start_length(a::AbstractFloat, len::Integer) = range_start_step_length(a, oftype(a, 1), len)
-range_start_length(a,                len::Integer) = range_start_step_length(a, oftype(a-a, 1), len)
-
-range_start_stop(start, stop) = start:stop
-
-function range_start_step_length(a::AbstractFloat, step::AbstractFloat, len::Integer)
-    range_start_step_length(promote(a, step)..., len)
-end
-
-function range_start_step_length(a::Real, step::AbstractFloat, len::Integer)
-    range_start_step_length(float(a), step, len)
-end
-
-function range_start_step_length(a::AbstractFloat, step::Real, len::Integer)
-    range_start_step_length(a, float(step), len)
+# Stop and length as the only argument
+function range_stop_length(a, len::Integer)
+    step = oftype(a - a, 1) # assert that step is representable
+    start = a - (len - oneunit(len))
+    if start isa Signed
+        # overflow in recomputing length from stop is okay
+        return UnitRange(start, oftype(start, a))
+    end
+    return range_step_stop_length(oftype(a - a, 1), a, len)
 end
 
-function range_start_step_length(a::T, step::T, len::Integer) where {T <: AbstractFloat}
-    _rangestyle(OrderStyle(T), ArithmeticStyle(T), a, step, len)
+# Start and length as the only argument
+function range_start_length(a, len::Integer)
+    step = oftype(a - a, 1) # assert that step is representable
+    stop = a + (len - oneunit(len))
+    if stop isa Signed
+        # overflow in recomputing length from stop is okay
+        return UnitRange(oftype(stop, a), stop)
+    end
+    return range_start_step_length(a, oftype(a - a, 1), len)
 end
 
-function range_start_step_length(a::T, step, len::Integer) where {T}
-    _rangestyle(OrderStyle(T), ArithmeticStyle(T), a, step, len)
-end
+range_start_stop(start, stop) = start:stop
 
-function _rangestyle(::Ordered, ::ArithmeticWraps, a, step, len::Integer)
-    start = a + zero(step)
-    stop = a + step * (len - 1)
-    T = typeof(start)
-    return StepRange{T,typeof(step)}(start, step, convert(T, stop))
-end
-function _rangestyle(::Any, ::Any, a, step, len::Integer)
-    start = a + zero(step)
-    T = typeof(a)
-    return StepRangeLen{typeof(start),T,typeof(step)}(a, step, len)
+function range_start_step_length(a, step, len::Integer)
+    stop = a + step * (len - oneunit(len))
+    if stop isa Signed
+        # overflow in recomputing length from stop is okay
+        return StepRange{typeof(stop),typeof(step)}(convert(typeof(stop), a), step, stop)
+    end
+    return StepRangeLen{typeof(stop),typeof(a),typeof(step)}(a, step, len)
 end
 
 range_start_step_stop(start, step, stop) = start:step:stop
@@ -893,7 +883,7 @@ _in_unit_range(v::UnitRange, val, i::Integer) = i > 0 && val <= v.stop && val >=
 function getindex(v::UnitRange{T}, i::Integer) where T
     @inline
     i isa Bool && throw(ArgumentError("invalid index: $i of type Bool"))
-    val = convert(T, v.start + (i - 1))
+    val = convert(T, v.start + (i - oneunit(i)))
     @boundscheck _in_unit_range(v, val, i) || throw_boundserror(v, i)
     val
 end
@@ -904,7 +894,7 @@ const OverflowSafe = Union{Bool,Int8,Int16,Int32,Int64,Int128,
 function getindex(v::UnitRange{T}, i::Integer) where {T<:OverflowSafe}
     @inline
     i isa Bool && throw(ArgumentError("invalid index: $i of type Bool"))
-    val = v.start + (i - 1)
+    val = v.start + (i - oneunit(i))
     @boundscheck _in_unit_range(v, val, i) || throw_boundserror(v, i)
     val % T
 end
@@ -919,7 +909,7 @@ end
 function getindex(v::AbstractRange{T}, i::Integer) where T
     @inline
     i isa Bool && throw(ArgumentError("invalid index: $i of type Bool"))
-    ret = convert(T, first(v) + (i - 1)*step_hp(v))
+    ret = convert(T, first(v) + (i - oneunit(i))*step_hp(v))
     ok = ifelse(step(v) > zero(step(v)),
                 (ret <= last(v)) & (ret >= first(v)),
                 (ret <= first(v)) & (ret >= last(v)))
@@ -949,13 +939,14 @@ end
 
 function unsafe_getindex(r::LinRange, i::Integer)
     i isa Bool && throw(ArgumentError("invalid index: $i of type Bool"))
-    lerpi(i-1, r.lendiv, r.start, r.stop)
+    lerpi(i-oneunit(i), r.lendiv, r.start, r.stop)
 end
 
 function lerpi(j::Integer, d::Integer, a::T, b::T) where T
     @inline
-    t = j/d
-    T((1-t)*a + t*b)
+    t = j/d # ∈ [0,1]
+    # compute approximately fma(t, b, -fma(t, a, a))
+    return T((1-t)*a + t*b)
 end
 
 getindex(r::AbstractRange, ::Colon) = copy(r)
@@ -968,8 +959,10 @@ function getindex(r::AbstractUnitRange, s::AbstractUnitRange{T}) where {T<:Integ
         return range(first(s) ? first(r) : last(r), length = last(s))
     else
         f = first(r)
-        start = oftype(f, f + first(s)-firstindex(r))
-        return range(start, length=length(s))
+        start = oftype(f, f + first(s) - firstindex(r))
+        len = length(s)
+        stop = oftype(f, start + (len - oneunit(len)))
+        return range(start, stop)
     end
 end
 
@@ -984,11 +977,14 @@ function getindex(r::AbstractUnitRange, s::StepRange{T}) where {T<:Integer}
     @boundscheck checkbounds(r, s)
 
     if T === Bool
-        return range(first(s) ? first(r) : last(r), step=oneunit(eltype(r)), length = last(s))
+        return range(first(s) ? first(r) : last(r), step=oneunit(eltype(r)), length=last(s))
     else
         f = first(r)
-        start = oftype(f, f + s.start-firstindex(r))
-        return range(start, step=step(s), length=length(s))
+        start = oftype(f, f + s.start - firstindex(r))
+        st = step(s)
+        len = length(s)
+        stop = oftype(f, start + (len - oneunit(len)) * st)
+        return range(start, stop; step=st)
     end
 end
 
@@ -1011,9 +1007,13 @@ function getindex(r::StepRange, s::AbstractRange{T}) where {T<:Integer}
         return range(start, step=step(r); length=len)
     else
         f = r.start
+        fs = first(s)
         st = r.step
-        start = oftype(f, f + (first(s)-oneunit(first(s)))*st)
-        return range(start; step=st*step(s), length=length(s))
+        start = oftype(f, f + (fs - oneunit(fs)) * st)
+        st = st * step(s)
+        len = length(s)
+        stop = oftype(f, start + (len - oneunit(len)) * st)
+        return range(start, stop; step=st)
     end
 end
 
@@ -1042,7 +1042,7 @@ function getindex(r::StepRangeLen{T}, s::OrdinalRange{S}) where {T, S<:Integer}
         # Find closest approach to offset by s
         ind = LinearIndices(s)
         offset = L(max(min(1 + round(L, (r.offset - first(s))/sstep), last(ind)), first(ind)))
-        ref = _getindex_hiprec(r, first(s) + (offset-1)*sstep)
+        ref = _getindex_hiprec(r, first(s) + (offset - oneunit(offset)) * sstep)
         return StepRangeLen{T}(ref, rstep*sstep, len, offset)
     end
 end

stdlib/Dates/test/periods.jl

@@ -179,10 +179,8 @@ end
     @test_throws InexactError y * 3//4
     @test (1:1:5)*Second(5) === Second(5)*(1:1:5) === Second(5):Second(5):Second(25) === (1:5)*Second(5)
     @test collect(1:1:5)*Second(5) == Second(5)*collect(1:1:5) == (1:5)*Second(5)
-    @test (Second(2):Second(2):Second(10))/Second(2) === 1.0:1.0:5.0
-    @test collect(Second(2):Second(2):Second(10))/Second(2) == 1:1:5
-    @test (Second(2):Second(2):Second(10)) / 2 === Second(1):Second(1):Second(5)
-    @test collect(Second(2):Second(2):Second(10)) / 2 == Second(1):Second(1):Second(5)
+    @test (Second(2):Second(2):Second(10))/Second(2) === 1.0:1.0:5.0 == collect(Second(2):Second(2):Second(10))/Second(2)
+    @test (Second(2):Second(2):Second(10)) / 2 == Second(1):Second(1):Second(5) == collect(Second(2):Second(2):Second(10)) / 2
     @test Dates.Year(4) / 2 == Dates.Year(2)
     @test Dates.Year(4) / 2f0 == Dates.Year(2)
     @test Dates.Year(4) / 0.5 == Dates.Year(8)

stdlib/LinearAlgebra/test/special.jl

@@ -395,12 +395,18 @@ using .Main.Furlongs
     @test one(S) isa SymTridiagonal
 
     # eltype with dimensions
-    D = Diagonal{Furlong{2, Int64}}([1, 2, 3, 4])
-    Bu = Bidiagonal{Furlong{2, Int64}}([1, 2, 3, 4], [1, 2, 3], 'U')
-    Bl =  Bidiagonal{Furlong{2, Int64}}([1, 2, 3, 4], [1, 2, 3], 'L')
-    T = Tridiagonal{Furlong{2, Int64}}([1, 2, 3], [1, 2, 3, 4], [1, 2, 3])
-    S = SymTridiagonal{Furlong{2, Int64}}([1, 2, 3, 4], [1, 2, 3])
-    mats = [D, Bu, Bl, T, S]
+    D0 = Diagonal{Furlong{0, Int64}}([1, 2, 3, 4])
+    Bu0 = Bidiagonal{Furlong{0, Int64}}([1, 2, 3, 4], [1, 2, 3], 'U')
+    Bl0 =  Bidiagonal{Furlong{0, Int64}}([1, 2, 3, 4], [1, 2, 3], 'L')
+    T0 = Tridiagonal{Furlong{0, Int64}}([1, 2, 3], [1, 2, 3, 4], [1, 2, 3])
+    S0 = SymTridiagonal{Furlong{0, Int64}}([1, 2, 3, 4], [1, 2, 3])
+    F2 = Furlongs.Furlong{2}(1)
+    D2 = Diagonal{Furlong{2, Int64}}([1, 2, 3, 4].*F2)
+    Bu2 = Bidiagonal{Furlong{2, Int64}}([1, 2, 3, 4].*F2, [1, 2, 3].*F2, 'U')
+    Bl2 =  Bidiagonal{Furlong{2, Int64}}([1, 2, 3, 4].*F2, [1, 2, 3].*F2, 'L')
+    T2 = Tridiagonal{Furlong{2, Int64}}([1, 2, 3].*F2, [1, 2, 3, 4].*F2, [1, 2, 3].*F2)
+    S2 = SymTridiagonal{Furlong{2, Int64}}([1, 2, 3, 4].*F2, [1, 2, 3].*F2)
+    mats = Any[D0, Bu0, Bl0, T0, S0, D2, Bu2, Bl2, T2, S2]
     for A in mats
         @test iszero(zero(A))
         @test isone(one(A))

test/ranges.jl

@@ -1517,8 +1517,10 @@ isdefined(Main, :Furlongs) || @eval Main include("testhelpers/Furlongs.jl")
 using .Main.Furlongs
 
 @testset "dimensional correctness" begin
-    @test length(Vector(Furlong(2):Furlong(10))) == 9
-    @test length(range(Furlong(2), length=9)) == checked_length(range(Furlong(2), length=9)) == 9
+    @test_throws TypeError Furlong(2):Furlong(10)
+    @test_throws TypeError range(Furlong(2), length=9)
+    @test length(Vector(Furlong(2):Furlong(1):Furlong(10))) == 9
+    @test length(range(Furlong(2), step=Furlong(1), length=9)) == checked_length(range(Furlong(2), step=Furlong(1), length=9)) == 9
     @test @inferred(length(StepRange(Furlong(2), Furlong(1), Furlong(1)))) == 0
     @test Vector(Furlong(2):Furlong(1):Furlong(10)) == Vector(range(Furlong(2), step=Furlong(1), length=9)) == Furlong.(2:10)
     @test Vector(Furlong(1.0):Furlong(0.5):Furlong(10.0)) ==
@@ -2257,3 +2259,19 @@ let r = Ptr{Cvoid}(20):-UInt(2):Ptr{Cvoid}(10)
     @test step(r) === -UInt(2)
     @test last(r) === Ptr{Cvoid}(10)
 end
+
+# test behavior of wrap-around and promotion of empty ranges (#35711)
+@test length(range(0, length=UInt(0))) === UInt(0)
+@test isempty(range(0, length=UInt(0)))
+@test length(range(typemax(Int), length=UInt(0))) === UInt(0)
+@test isempty(range(typemax(Int), length=UInt(0)))
+@test length(range(0, length=UInt(0), step=UInt(2))) == UInt(0)
+@test isempty(range(0, length=UInt(0), step=UInt(2)))
+@test length(range(typemax(Int), length=UInt(0), step=UInt(2))) === UInt(0)
+@test isempty(range(typemax(Int), length=UInt(0), step=UInt(2)))
+@test length(range(typemax(Int), length=UInt(0), step=2)) === UInt(0)
+@test isempty(range(typemax(Int), length=UInt(0), step=2))
+@test length(range(typemax(Int), length=0, step=UInt(2))) === 0
+@test isempty(range(typemax(Int), length=0, step=UInt(2)))
+
+@test length(range(1, length=typemax(Int128))) === typemax(Int128)

test/testhelpers/Furlongs.jl

@@ -15,13 +15,26 @@ end
 Furlong(x::T) where {T<:Number} = Furlong{1,T}(x)
 Furlong(x::Furlong) = x
 (::Type{T})(x::Furlong{0}) where {T<:Number} = T(x.val)::T
+(::Type{T})(x::Furlong{0}) where {T<:Furlong{0}} = T(x.val)::T
+(::Type{T})(x::Furlong{0}) where {T<:Furlong} = typeassert(x, T)
 Furlong{p}(v::Number) where {p} = Furlong{p,typeof(v)}(v)
-Furlong{p}(x::Furlong{q}) where {p,q} = (@assert(p==q); Furlong{p,typeof(x.val)}(x.val))
-Furlong{p,T}(x::Furlong{q}) where {T,p,q} = (@assert(p==q); Furlong{p,T}(T(x.val)))
+Furlong{p}(x::Furlong{q}) where {p,q} = (typeassert(x, Furlong{p}); Furlong{p,typeof(x.val)}(x.val))
+Furlong{p,T}(x::Furlong{q}) where {T,p,q} = (typeassert(x, Furlong{p}); Furlong{p,T}(T(x.val)))
 
 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{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{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.one(x::Furlong{p,T}) where {p,T} = one(T)
 Base.one(::Type{Furlong{p,T}}) where {p,T} = one(T)
 Base.oneunit(x::Furlong{p,T}) where {p,T} = Furlong{p,T}(one(T))