On Thu, Apr 18, 2019 at 11:05:10PM -0400, Nick Sabalausky (Abscissa) via Digitalmars-d wrote:
> On 4/18/19 1:01 AM, H. S. Teoh wrote:
> > Got bitten by this today:
> > 
> 
> Yeeouch! Bugzilla issue #?

Just filed a new bug:

	https://issues.dlang.org/show_bug.cgi?id=19812


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On Fri, Apr 19, 2019 at 10:17:08PM +0000, Suleyman via Digitalmars-d wrote:
> On Thursday, 18 April 2019 at 05:01:17 UTC, H. S. Teoh wrote:
> > ...
> 
> Sneaky enough.
> The problem is the value copy semantics of S which results in an
> address to a dead stack frame being saved.
> If you make it a ref parameter the issue goes away.
[...]

Using ref solves it for this specific case, but will still exhibit the same problem if the struct referenced by the ref is a temporary due to other factors.  E.g., if you pass the struct to a function that then returns map!(S.method) back to the caller, then the ref will still be referencing a temporary that goes out of scope while the lambda still holds the reference.

The underlying problem is that the lambda closes over a variable whose lifetime is not guaranteed to be at least the lifetime of the lambda. It's exactly this sort of scoping issues that -dip1000 is supposed to prevent, but it seems somehow this case was missed.


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