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digitalmars.D - Array implicit conversions subvert type system

reply Mike Capp <mike.capp gmail.com> writes:
Can't remember if I raised this before (it was loitering among the testcases
from my last peek at D), but it's still true in 0.174. "Derived[] to Base[]"
assignments really shouldn't happen without either a copy or an explit cast.

---

class Fruit {};
class Apple : Fruit {};
class Orange : Fruit {};

void main()
{
	Apple[] apples;
	apples.length = 3;
	Fruit[] fruits = apples;
	Orange orange = new Orange;
	fruits[1] = orange;

	if (apples[1] == orange) printf("Oops.\n");
}
Nov 24 2006
parent reply Gregor Richards <Richards codu.org> writes:
Mike Capp wrote:
 Can't remember if I raised this before (it was loitering among the testcases
 from my last peek at D), but it's still true in 0.174. "Derived[] to Base[]"
 assignments really shouldn't happen without either a copy or an explit cast.
 
 ---
 
 class Fruit {};
 class Apple : Fruit {};
 class Orange : Fruit {};
 
 void main()
 {
 	Apple[] apples;
 	apples.length = 3;
 	Fruit[] fruits = apples;
 	Orange orange = new Orange;
 	fruits[1] = orange;
 
 	if (apples[1] == orange) printf("Oops.\n");
 }

No, purposeful, contrived subversion of the type system subverts the type system. - Gregor Richards
Nov 24 2006
parent reply Mike Capp <mike.capp gmail.com> writes:
Gregor Richards wrote:
 No, purposeful, contrived subversion of the type
 system subverts the type system.

Purposeful, contrived subversion of the type system should be marked as such with a cast, IMHO. That's what casts are for. It's hardly a burden for the programmer, and it prevents accidents. This crops up in basic OO FAQs for a reason. It's a real mistake that real people make.
Nov 24 2006
parent Gregor Richards <Richards codu.org> writes:
void eatFruit(Fruit[] yum) { ... }

void pickApples()
{
     Apple[] a;
     for (int i = 0; i < 100; i++) { a ~= new Apple(); }
     eatFruit(a); // nope, can't eat it, it's Apples, not fruit
}
Nov 24 2006