Why doesn't this function compile

General Usage
3

It depends on what @atteson was hoping to accomplish. I read the code as an attempt to force the element type of the AbstractVector y to be the same as the type of the argument passed into f1.

If that was the intent then adding the second where T won’t work since T gets bound to a different type in f2:

julia> function f1( x::T ) where {T}
                  function f2( y::U ) where {U <: AbstractVector{T}} where T
                                 return 0.0
                  end
                  return f2
              end
f1 (generic function with 1 method)

julia> a = f1(1.0)
(::var"#f2#12") (generic function with 1 method)

julia> a(["this","that"])
0.0

This alternative forces the element type of y to be the same as the type of the argument to f1:

julia> function f1(x::T ) where {T}
           function f2(y::AbstractVector{T})
               return 0.0
           end
           return f2
       end
f1 (generic function with 1 method)

julia> a = f1(1.0)
(::var"#f2#11"{Float64}) (generic function with 1 method)

julia> a([1.0,2.0])
0.0

julia> a([1,2])
ERROR: MethodError: no method matching (::var"#f2#11"{Float64})(::Vector{Int64})
Closest candidates are:
  (::var"#f2#11"{T})(::AbstractVector{T}) where T at REPL[24]:2
Stacktrace:
 [1] top-level scope
   @ REPL[27]:clock130:
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