Re: Array bound checks removal increasing importance

[bearophile via Digitalmars-d]

Wanderer:

void main() {
   int[5] data;
   foreach (const i; 0 .. 10)
       data[i] = 0;
   foreach (immutable i; 0 .. 10)
       data[i] = 0;
   int[10] big;
   foreach (const i, x; big)
       data[i] = x;
}

I'm not sure if bound checks should be removed here. Before 
removal, this code gives safe runtime exception, or, as 
suggested above, compile-time error.

The compiler should catch all those cases at compile-time :-)


But the compiler must recognize this as correct code:


void main() {
   int[5] data;
   foreach (const i; 0 .. 10)
       if (i < 5)
           data[i] = 0;
}

My personal opinion is that code like this should remain 
inefficient, to stimulate programmers to use simpler, easier to 
understand idioms, like foreach (i; data).

Java already removes several bound checks but this only increases 
the array access performance, so it's not easy to see, unless you 
do benchmarks (or in D compare the run-time with the run-time 
with disabled array bound tests). So I don't think this compiler 
improvement is going to worsen the D code you will see around :-)

Bye,
bearophile