OpenEuphoria

Re: Functions vs. parameters

• Posted by Robert Craig <rds at EMAIL.MSN.COM> Oct 12, 1998
• 628 views

Jay Turley writes:
> If I pass a parameter to a function, and the same parameter
> is returned by that function, what is the overhead cost associated
> with it, i.e. am I wasting time copying the object into memory?
> Is a copy of that object actually sent?  I would assume so, because
> if a function acts on a parameter and doesn't return it, the original
> copy is unchanged.

The way things work internally is pretty simple.
Euphoria only goes to the trouble of making a copy of a
sequence when it's really necessary.
If you pass a sequence s to a function foo:

      s = {1,2,3,{4,5,6,7}}
      x = foo(s)

only a pointer to s is passed. The elements
contained in s are *not* copied. Suppose foo() looks like:

          function foo(sequence t)
                return t[1]
          end function

then while foo() is executing, t and s point at the same data in memory.
Since t is not modified, there is never any reason to make
a copy. If however you have something like:

          function foo(sequence t)
               t[3] = 99
               return t
          end function

then at the point that t[3] is set to 99 it will no longer
be possible for t and s to point at the same data
in memory - the interpreter will create a new
sequence in memory {1,2,99,{4,5,6,7}} and t will point to it,
while s continues to point at the original sequence.

Note that the {4,5,6,7} element of s will *not* be copied.
Only the "top-level" elements need to be copied.
A single copy of {4,5,6,7} will be pointed to from s[4] and t[4].

Regards,
     Rob Craig
     Rapid Deployment Software
     http://members.aol.com/FilesEu/