better fallback ::Integer methods for flipsign and cmp

[JeffreySarnoff]

(It happened yesterday, a holdover from v0.2)

while trying approaches to keeping SafeInt types stickier than Ints
(a) just follow JuliaMath/IntegerRounding
(b) (a) with specific conversions xor constructions
(c) (a) with specific conversions and constructions
at some point, these errors occur, each as the prior is fixed

flipsign not defined for SafeInt64
( flipsign(SafeInt64, Int64), -SafeInt64, SafeInt<SafeInt were defined )

flipsign(flipee:SafeInt64, flipper::Int64)
could fallback to flipper < 0 ? -flippee : flippee
if that evaluates unexceptionally, the proper result is obtained, right?

< not defined for SafeInt64, Int64
( the conversions and promotions were defined )

cmp(x,y) could fallback to (cmp)(promote(x,y)...)
if that evaluates unexceptionally, the proper result is obtained, right?

dec not defined for ?

[KristofferC]

Perhaps it is because I am not a native speaker, but I am having quite a hard time understanding what the problem is. Perhaps you make a minimum example, with the expected output and the current output?

(also, please use code quotes)

[JeffreySarnoff]

I do not have access to the history now. Maybe Stefan remembers what makes the 'flipsign' error appear. Otherwise, when I am at that machine I will try to isolate this.

[JeffreySarnoff]

@StefanKarpinski remember this -- the fallback first to a flipsign error and then to a dec error when defining a new low level arithmetic type?

[StefanKarpinski]

I'm afraid I don't recall this. When did we discuss it?

[JeffreySarnoff]

2013

[JeffreySarnoff]

I will try to re-create it tonight

[stevengj]

@JeffreySarnoff, we already have a fallback method for flipsign, as well as more specific flipsign fallbacks for integer types. Why aren't these working for you? Which method of flipsign is being called?

Is SafeInt64 a subtype of Signed?

[JeffreySarnoff]

Is SafeInt64 a subtype of Signed? yes

[JeffreySarnoff]

v0.7.0-DEV

sizeof(Int) == 8

abstract type SafeSigned <: Signed end

primitive type SafeInt64 <: SafeSigned 64 end

Base.convert(::Type{SafeInt64}, x::Int64)     = reinterpret(SafeInt64, x)
Base.convert(::Type{Int64},     x::SafeInt64) = reinterpret(Int64, x)

s64 = SafeInt64(3)

Error showing value of type SafeInt64:
ERROR: flipsign not defined for SafeInt64

[KristofferC]

0.6

julia> s64 = SafeInt64(3)
Error showing value of type SafeInt64:
ERROR: circular method definition: promotion of types SafeInt64 and SafeInt64 failed to change any input types
Stacktrace:
 [1] error(::String, ::String, ::Vararg{String,N} where N) at /Applications/Julia-0.6.app/Contents/Resources/julia/lib/julia/sys.dylib:?
 [2] sametype_error(::SafeInt64, ::Vararg{SafeInt64,N} where N) at ./promotion.jl:244
 [3] promote_noncircular at ./promotion.jl:219 [inlined]
 [4] flipsign at ./int.jl:75 [inlined]
 [5] abs at ./int.jl:112 [inlined]
 [6] dec(::SafeInt64) at ./intfuncs.jl:492
 [7] show at ./show.jl:259 [inlined]
 [8] show at ./replutil.jl:4 [inlined]

[JeffreySarnoff]

0.7-DEV

julia> s64 = SafeInt64(3)
Error showing value of type SafeInt64:
ERROR: flipsign not defined for SafeInt64
Stacktrace:
 [1] error(::String, ::String, ::Type) at ./error.jl:44
 [2] dec(::SafeInt64) at ./intfuncs.jl:654
 [3] show(::IOContext{Base.Terminals.TTYTerminal}, ::SafeInt64) at ./show.jl:353
 [4] show(::IOContext{Base.Terminals.TTYTerminal}, ::MIME{Symbol("text/plain")}, ::SafeInt64) at ./replutil.jl:4
 [5] display(::Base.REPL.REPLDisplay{Base.REPL.LineEditREPL}, ::MIME{Symbol("text/plain")}, ::SafeInt64) at ./repl/REPL.jl:125
 [6] display(::Base.REPL.REPLDisplay{Base.REPL.LineEditREPL}, ::SafeInt64) at ./repl/REPL.jl:128
 [7] display(::SafeInt64) at ./multimedia.jl:277
 [8] (::getfield(Base, Symbol("#inner#4")){Array{Any,1},typeof(display),Tuple{SafeInt64}})() at ./essentials.jl:669
 [9] print_response(::Base.Terminals.TTYTerminal, ::Any, ::Void, ::Bool, ::Bool, ::Void) at ./repl/REPL.jl:146
 [10] print_response(::Base.REPL.LineEditREPL, ::Any, ::Void, ::Bool, ::Bool) at ./repl/REPL.jl:132
 [11] (::getfield(Base.REPL, Symbol("#do_respond#17")){Bool,getfield(Base.REPL, Symbol("##27#37")){Base.REPL.LineEditREPL,Base.REPL.REPLHistoryProvider},Base.REPL.LineEditREPL,Base.LineEdit.Prompt})(::Base.LineEdit.MIState, ::Base.GenericIOBuffer{Array{UInt8,1}}, ::Bool) at ./repl/REPL.jl:674
 [12] (::getfield(Base.REPL, Symbol("##32#42")))(::Base.LineEdit.MIState, ::Base.REPL.LineEditREPL, ::Vararg{Any,N} where N) at ./repl/REPL.jl:929
 [13] (::getfield(Base.LineEdit, Symbol("##19#20")){getfield(Base.REPL, Symbol("##32#42")),String})(::Base.LineEdit.MIState, ::Base.REPL.LineEditREPL) at ./repl/LineEdit.jl:1059
 [14] prompt!(::Base.Terminals.TTYTerminal, ::Base.LineEdit.ModalInterface, ::Base.LineEdit.MIState) at ./repl/LineEdit.jl:2061
 [15] run_interface(::Base.Terminals.TTYTerminal, ::Base.LineEdit.ModalInterface) at ./repl/LineEdit.jl:1962
 [16] run_frontend(::Base.REPL.LineEditREPL, ::Base.REPL.REPLBackendRef) at ./repl/REPL.jl:986
 [17] run_repl(::Base.REPL.LineEditREPL, ::getfield(Base, Symbol("##566#567"))) at ./repl/REPL.jl:182
 [18] _start() at ./client.jl:448

[KristofferC]

julia/base/promotion.jl

Line 387 in e45961d

flipsign(x::T, y::T) where {T<:Signed} = no_op_err("flipsign", T)

[stevengj]

That's weird, I wonder why we have that fallback, given that we have a generic flipsign(::Real, ::Real) fallback. Is it to prevent a dispatch loop somewhere?

[KristofferC]

Yes, #23491, #22801 (related to the error on 0.6)

[stevengj]

Seems like the fix should be to have the fallback call the ::Real version (either by invoke, if that is fast nowadays, or by refactoring have them both call _flipsign or something).

[JeffreySarnoff]

and better fallback ::Unsigned methods too .. things work better when each (Signed, Unsigned) is separately backstopped (otherwise Bool <: Integer can make less obvious demands on the type writer)