Pass by Value-Result/Copy

Implementation Option: Value Only

• Time Wasted: Copying
• Space Wasted: Duplicates
• Order of Parameter Evaluation

  call subpgm(a, a); // Value of a?
  

  • Specified in Language or
  • Implementation Dependent: Not Portable

Traditional Implementation in Algol-60 Descendants:

• On function call: Copy rvalue from actual parameter to formal parameter
• On function return: Copy rvalue from formal parameter to actual parameter

Value-Result is equivalent to Reference except when aliasing is involved:

int global = 10;
...
int local = 5;
call subpgm( global, local );
print global;   // What is printed?
print local;

void subpgm( int first, int second )
{
  first = 20;
  second = 15;
  global = 25;
}