Conditional Assignment
This special assignment is intended to change a property
or other variable that has already a default value, when a new value
is given.
The := symbol assign conditionally a variable, if the expression
is not nil .
The error structure is set to "true" if the expression to
assign is nil.
Example:
x := z
error ? print "z is nil"
The above assignment is equivalent to:
if (z nil) let x = z
Only simple assignments may be conditional and can use the :=
symbol.
Examples og conditional assignments. When x is not assigned, the 15 value is assigned to it, then the 100 values also but is null and is not assigned. |
int
x int y = null x := 15 x := 100 x := y print x |
Display: | > 100 |
Exercises |
1) In the following program, x is set to null, guess what
the program will assign, "ok" or "not assigned"? Verify by writting the program. int x = null int y = 25 x := y if x = null print "not assigned" else print "ok" /if Answer (run the program) |