http://d.puremagic.com/issues/show_bug.cgi?id=9087
Summary: Value modified in foreach warning
Product: D
Version: D2
Platform: All
OS/Version: All
Status: NEW
Severity: enhancement
Priority: P2
Component: DMD
AssignedTo: [email protected]
ReportedBy: [email protected]
--- Comment #0 from [email protected] 2012-11-27 18:41:03 PST ---
Currently (DMD 2.061alpha) this code generates a warning:
// program#1
void main() {
foreach (i; 0 .. 10)
i++;
}
test.d(4): Warning: variable modified in foreach body requires ref storage
class
This is a rather common and well known source of bugs in D code (C# disallows
such mutation):
// program#2
struct S { int x; }
void main() {
auto items = [S(1), S(2), S(3)];
foreach (it; items)
it.x++;
}
(The bug is that the programmer thinks she has modified the contents of "items"
array, while the changes are just in the "it" copy, and such changes get lost
silently.)
So to both help avoid those common bugs, and improve consistency between the
two cases, I suggest to generate a warning in program#2 too, similar to:
test.d(6): Warning: mutable value modified in foreach body requires ref storage
class
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