ProjectTo maps to projecting onto the inner val, cleaner NoTangents in * pullback

Author: SBuercklin

src/chainrules.jl

@@ -5,27 +5,22 @@ function rrule(UT::Type{Quantity{T,D,U}}, x::Number) where {T,D,U}
     return unitful_x, uq_pullback
 end
 
-function ProjectTo(x::Quantity)
-    project_val = ProjectTo(x.val) # Project the literal number
-    return ProjectTo{typeof(x)}(; project_val = project_val)
-end
-
 function (projector::ProjectTo{<:Quantity})(x::Number)
     new_val = projector.project_val(ustrip(x))
     return new_val*unit(x)
 end
 
 # Project Unitful Quantities onto numerical types by projecting the value and carrying units
+ProjectTo(x::Quantity) = ProjectTo(x.val)
+
 (project::ProjectTo{<:Real})(dx::Quantity) = project(ustrip(dx))*unit(dx)
 (project::ProjectTo{<:Complex})(dx::Quantity) = project(ustrip(dx))*unit(dx)
 
 function rrule(::typeof(*), x::Quantity, y::Units, z::Units...)
     Ω = *(x, y, z...)
-    project_x = ProjectTo(x)
     function times_pb(Δ)
-        δ = project_x(Δ)
-        units = (y, z...)
-        return (NoTangent(), *(δ, y, z...), ntuple(_ -> NoTangent(), length(units))...)
+        nots = ntuple(_ -> NoTangent(), 1 + length(z))
+        return (NoTangent(), *(ProjectTo(x)(Δ), y, z...), nots...)
     end
     return Ω, times_pb
 end