Implicit static->dynamic arr and modifying

[H. S. Teoh via Digitalmars-d-learn]

On Wed, May 07, 2014 at 06:31:15PM +0000, Rene Zwanenburg via Digitalmars-d-learn wrote:
> On Wednesday, 7 May 2014 at 15:41:19 UTC, Nick Sabalausky wrote:
> >On 5/6/2014 6:46 PM, Rene Zwanenburg wrote:
[...]
> >>struct S
> >>{
> >>    @safe:
> >>    string str;
> >>
> >>    this(string data)
> >>    {
> >>        import std.digest.md;
> >>        str = md5Of(data).toHexString(); // Oops...
> >>    }
> >>}
> >
> >That must be a terribly subtle one, I'm not seeing the problem at
> >all.
> >
> >I get that md5Of returns a static array, and then a slice of it gets
> >passed to toHexString, but AIUI toHexString finishes (and returns a
> >newly allocated string) before the temporary static array leaves
> >scope.
> 
> toHexString has an overload that takes a static array and can
> therefore return a static array (the length is known to be twice the
> input length). In essence it's the same bug as directly storing the
> result of md5Of, but this was the exact line that was causing me
> grief. Indeed, it looks innocent enough..
> 
> So, toHexString returns a static array, which can be implicitly
> assigned to a member slice. In @safe code. I was horrified ;). Imo
> it's one of the most serious violations of D's safe by default
> principle.

Ouch!! Wow, that's really nasty. :-(  It totally went by me, even though
I've been bitten before by the variadic ctor bug.


T

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