Automatically parameterizing a type

General Usage Performance
4

I realize the above is not exactly the requested feature so…here you go:

macro params(struct_expr)
   name = struct_expr.args[2]
   fields = @view struct_expr.args[3].args[2:2:end]
   params = []
   for i in 1:length(fields)
           x = fields[i]
           T = gensym()
           if x isa Symbol
                   push!(params, T)
                   fields[i] = :($x::$T)
           elseif x.head == :(::)
                   abstr = x.args[2]
                   var = x.args[1]
                   push!(params, :($T <: $abstr))
                   fields[i] = :($var::$T)
           end
   end
   if name isa Symbol && length(params) > 0
           struct_expr.args[2] = :($name{$(params...)})
   elseif name.head == :curly
           append!(struct_expr.args[2].args, params)
   else
           error("Unidentified type definition.")
   end

   esc(struct_expr)
end

julia> @params struct MyType
           a::Integer
           b
       end

julia> MyType(1,2)
MyType{Int64,Int64}(1, 2)

julia> MyType(1.0,2)
ERROR: MethodError: no method matching MyType(::Float64, ::Int64)
Closest candidates are:
  MyType(::##360<:Integer, ::##361) where {##360<:Integer, ##361} at REPL[2]:2
Stacktrace:
 [1] top-level scope at none:0
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