Error: cannot instantiate: 'T'

[sflennik]

I'm trying to write a generic function, here is a simplified version. It 
generates the errors shown below. What am I doing wrong?
    
    
    import strutils
    
    proc test16(): uint16 =
      var buffer: array[sizeof(uint16), uint8]
      for ix in 0..sizeof(uint16)-1:
        buffer[ix] = cast [uint8](ix)
      result = cast[uint16](buffer)
    
    proc test[T](): T =
      var buffer: array[sizeof(T), uint8]
      for ix in 0..sizeof(T)-1:
        buffer[ix] = cast [uint8](ix)
      result = cast[T](buffer)
    
    var value16: uint16 = test16()
    echo "value16 = ", toHex(value16)
    
    var valueT: uint16 = test()
    echo "valueT = ", toHex(valueT)
    

Here are the errors: 
    
    
    # t2.nim(18, 26) template/generic instantiation from here
    # t2.nim(9, 11) Error: cannot instantiate: 'T'