Comparing Exceptions and Errors

[Ali Çehreli]

On 6/5/22 08:07, kdevel wrote:
 > On Sunday, 5 June 2022 at 14:24:39 UTC, Ali Çehreli wrote:
 > [...]
 >> struct S {
 >>   int[] a;
 >>   int[] b;
 >>
 >>   void add(int i) {    // <-- Both arrays always same size
 >>     a ~= i;
 >>     b ~= i * 10;
 >>   }
 >>
 >>   void foo() {
 >>     assert(a.length == b.length);  // <-- Invariant check
 >>     // ...
 >>   }
 >> }
 >>
 >> void main() {
 >>   auto s = S();
 >>   s.add(42);
 >>   s.foo();
 >> }
 >>
 >> The code is written in a way that both arrays will *always* have equal
 >> number of elements.
 >
 > I think this is what Sean Parent called "incidental data structure" [1].

Like many other programmers who include me, Sean Parent may be right.[1]

Other than being a trivial example to make a point, the code I've shown 
may be taking advantage of the "structure of array" optimization. I am 
sure Sean Parent knows that as well.

 > I would refactor the code:

Most likely me too.

 > struct T {
 >     int a;
 >     int b;
 > }
 >
 > struct S {
 >     T [] t;
 >
 >    void add(int i) {
 >      t ~= T (i, i * 10);
 >    }
 >
 >    void foo() {
 >                  // Look Ma no assert!

The assert may have been moved to another place:

struct T {
     int a;
     int b;

   invariant() {
     // Look Pa it's still here!
     assert(b == a * 10);
   }
}

Ali

[1] I stopped following Sean Parent when he dismissed D and me by waving 
his hand behind and walking away: "A language with reference types? No, 
thanks." That happened at the end of one of his presentations here at 
the Silicon Valley C++, which I happened to co-host. I am sure he is 
observant enough to one day realize that C++ has reference types by 
convention. (I recently posted links to C++ core guidelines proving that 
point of mine, one of which is something to the effect of "never pass 
polymorphic types by-value".)