julia> @eval Base begin
       @inline function __unsafe_string!(out, s::Symbol, offs::Integer)
           n = sizeof(s)
           GC.@preserve s out unsafe_copyto!(pointer(out, offs), unsafe_convert(Ptr{UInt8},s), n)
           return n
       end

       function string(a::Union{Char, String, SubString{String}, Symbol}...)
           n = 0
           for v in a
               if v isa Char
                   n += ncodeunits(v)
               else
                   n += sizeof(v)
               end
           end
           out = _string_n(n)
           offs = 1
           for v in a
               offs += __unsafe_string!(out, v, offs)
           end
           return out
       end
       end
string (generic function with 21 methods)