On Saturday, 21 May 2016 at 17:32:47 UTC, dan wrote:
Is it possible to have a class which has a variable which can
be seen from the outside, but which can only be modified from
the inside?
Something like:
class C {
int my_var = 3; // semi_const??
void do_something() { my_var = 4; }
}
And then in another file
auto c = new C();
c.my_var = 5; // <<<- should trigger a compile-time error
writeln("the value is ", c.my_var); // <<<- should print 3
c.do_something();
writeln("the value is ", c.my_var); // <<<- should print 4
Reading Alexandrescu's book suggests the answer is "no" (the
only relevant type qualifiers are private, package, protected,
public, and export, and none seem appropriate).
(This effect could be simulated by making my_var into a
function, but i don't want to do that.)
TIA for any info!
dan
You can create a const accessor for the variable. Then you can
have it be mutable internally but const externally.
Class C
{
int _my_var = 2;
void setMyVarTo3() { _my_var = 3; }
@property const(int) my_var() { return _my_var; }
}
auto c = new C();
writeln(c.my_var); //Prints 2
c.setMyVarTo3();
writeln(c.my_var); //Prints 3
c.my_var = 4; //Error, cannot modify const(int)
