Re: lambda : capturing a data member - is it legal?
Helmut Jarausch wrote:
Hi,
reading Scott Meyers' "Overview of the New C++" I stumbled over
#include <algorithm>
#include <list>
class Widget {
public:
void doSomething();
private:
std::list<int> li;
int minVal;
};
void Widget::doSomething() {
auto it = std::find_if(li.cbegin(), li.cend(),
[minVal](int i) { return i > minVal; } // error?
);
}
Scott says, that the second to last line is in error and 'repairs' it by
capturing 'this' instead of minVal.
On the other hand, gcc-4.5.2 accepts the code above.
I believe that you are right. You capture "minVal" by copy, and thus the use
of "minVal" is transformed to a access to the data member of the closure
type and in the end does't use the enclosing "Widget" object by the lambda-
expression itself.
BUT I think that the wording of N3225 renders your code ill-formed. It
requires that any identifier in the capture-clause names an automatic
variable declared in the reaching scope of the lambda. The reaching scope
only covers up to and including the inner-most enclosing function. The class
scope of that function, if the function is a class member, is lexically
outside that scope. Class members also doesn't necessarily have automatic
storage duration. So the wording of n3225 seems to forbid capturing class
members, but I don't think that's the intent (If I'm not missing something).
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