@generated inside macro: who's interpolating?

General Usage
10

I think the easiest solution here is to not define ex separately, but inside the generated function. You can then use $$ to interpolate twice, meaning the interpolated variable lives in the scope of Op2, like OP, A and B, or just interpolate once with $ to interpolate variables from the generated function’s scope, like T:

julia> macro Op2(OP,A,B)
           return esc(quote
               @generated function $OP(a::MyType{Ta},b::MyType{Tb}) where{Ta,Tb}
                   T = max(Ta,Tb)
                   return :(MyType{$T}($$OP(a.x*$$A,b.x*$$B)))
               end
           end)
       end
@Op2 (macro with 1 method)

julia> struct MyType{T} x end

julia> @Op2 Base.:+ 1 2

julia> MyType{1}(1) + MyType{2}(2)
MyType{2}(5)
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