Re: Call by reference vs. call by value

[dewar@cs.nyu.edu (Robert Dewar)]

Chris said

"Well, I guess I never conceived a machine might exist where call-by-
value for anything bigger than a word is more efficient than call by
reference, so my first instinct would be to dictate that
call-by-reference be used in all cases.  I believed the opposite was
true, however, because I wrongly thought that the designers of Ada
valued safety over performance, which is not really true."

Well as I hope is clear from my earlier post, your conception was not
broad enough :-)

Cases where values larger than one word are more efficiently passed by
copy:

  - when bit alignment is involved (packed case)
  - several words can be passed in registers (according to many ABI's)
  - caller and callee are in different address spaces

and here are undoubtedly more.

Note that the idea of allowing implementation freedom here is not new. 
Fortran-66 is quite explicit in leaving it up to the implementation
whether parameters are passed by value or reference.