Chris:
The following:
import std.stdio;
void main() {
int[5] arg;
arg[10] = 3; // Compiler says (of course):
Error: array index 10 is out of bounds arg[0 .. 5]
}
import std.stdio;
void main() {
int[5] arg;
foreach (i; 0..10) {
arg[i] = i;
}
}
Compiler says nothing, but we get a runtime error 'Range
violation'.
Bug or design?
Spotting the second bug is beyond the very limited analysis
capabilities of the D compiler. But a slightly different but
still rather common kind of code (where the index is not mutable)
could be spotted as buggy by the compiler:
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;
}
(In D it's very good to tag as const/immutable the indexes of
arrays, as work around a design bug of D foreach).
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;
}
So can we add this logic in the compiler?
Bye,
bearophile
