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Inadequate support of promote_rule for non-concrete types #343
Description
For better or worse, PR #207 is the most significant change in FPN v0.9.
However the current promote_rule for non-concrete types is somewhat imperfect.
In ColorTypes.jl, I am keenly aware that the handling of non-concrete types can lead to chaos.
Here, I’d like to think about ways to make things a little better, as long as they don’t go against common sense.
julia> promote_rule(Normed{UInt8, 8}, Fixed{Int8, 7})
Float32
julia> promote_rule(Normed{UInt8}, Fixed{Int8})
Union{} # -> Float32
julia> promote_rule(Normed{UInt8}, Normed{UInt8})
Union{} # -> Normed{UInt8}
julia> promote_rule(Normed{UInt8}, Normed{UInt16})
Union{} # -> Normed{UInt16}
julia> promote_rule(Normed{UInt8}, Normed)
Union{} # -> Normed
julia> promote_rule(Normed{UInt8}, Normed{Union{UInt8, UInt16}})
Union{} # -> Normed (Any desire to make this more strict is a path to despair.)
julia> promote_rule(Normed{UInt8}, FixedPoint)
Union{} # -> FixedPoint
julia> promote_rule(Normed{UInt8}, Float64)
Float64
julia> promote_rule(Normed, Float64)
ERROR: StackOverflowError # -> BigFloat
julia> promote_rule(Normed{UInt8}, Int8)
Float32
julia> promote_rule(Normed, Int8)
Normed # -> BigFloatSome of the unnatural promotions or stack overflow errors are caused by issue #342. In other words, fixing issue #342 will resolve some of these issues.
Activity
[-]`promote_rule` for non-concrete types[/-][+]Inadequate support of `promote_rule` for non-concrete types[/+]kimikage commentedon Sep 29, 2026
This is planned to be fixed in PR #341. However, since the impact is greater than originally anticipated, I will split the PR.