Hi,
On 2013-10-22 17:50, Sean McBride wrote:
On Tue, 22 Oct 2013 10:31:01 +0200, Daniel Höpfl said:
Was the old (non-arc) code faulty (but the compiler did not notice
this)?
Why is the arc-version (with TRIGGER_ERROR defined) wrong?
It is wrong in the non-arc world, too. (ISO/IEC 9899:2011 AKA C11,
6.8.6.1: "A goto statement shall not jump from outside the scope of an
identifier having a variably modified type to inside the scope of that
identifier" - switch is a special case of goto.)
Daniel,
I don't think you can quote the Standard about 'goto' and just wave
your hands and say it applies to 'switch' also. :) The Standard's
description of 'switch' should contain the answer.
OK ... but as you say, the standard should contain the answer. Next try:
C11, 6.8.4.2, paragraph 7 (The example): "the object whose identifier is
i exists with automatic storage duration (within the block) but is never
initialized, and thus if the controlling expression has a nonzero value,
the call to the printf function will access an indeterminate value."
(Using this paragraph because it compresses the scope/initializing topic
into one sentence.)
In your shorter example, the compiler does not complain for int*,
because it is okay for foo to be uninitialized.
If we use NSObject* as type of foo, this is okay for non-ARC, too.
With ARC, we have to include the ARC specification: "A retainable object
pointer is either a null pointer or a pointer to a valid object." -
<http://clang.llvm.org/docs/AutomaticReferenceCounting.html#retain-count-semantics>
Back to your example: foo is in scope but not initialized.
This is not acceptable for ARC (even if foo is not used in the scope).
So: clang is right. :-)
Maybe clang/ARC should simply init NSObject *foo with nil (even when the
Cxx standard says it is uninitialized in this case).
IMHO, that's pretty weird!
It is ... if you move the "default:" label to the top, it works with
ARC, too: C11, 6.8.4.2, p. 2 not met, foo's scope is now limited to
"case 1:".
Bye,
Daniel
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