C++0x lambda capture by value always const?

问题:

Is there any way to capture by value, and make the captured value non-const? I have a library functor that I would like to capture & call a method that is non-const but should be.

The following doesn't compile but making foo::operator() const fixes it.

struct foo {   bool operator () ( const bool & a )   {     return a;   } };   int _tmain(int argc, _TCHAR* argv[]) {   foo afoo;    auto bar = [=] () -> bool     {       afoo(true);     };    return 0; } 

回答1:

Use mutable.

 auto bar = [=] () mutable -> bool .... 

Without mutable you are declaring the operator () of the lambda object const.

回答2:

There is alternative way to using mutable (solution proposed by Crazy Eddie).

With [=] your block captures all objects by values. You can use [&] to capture all objects by reference:

auto bar = [&] () -> bool 

Or you can capture by reference only certain object [=, &afoo]:

auto bar = [=, &afoo] () -> bool 

Refer to this page for fore details (Explanation section): http://en.cppreference.com/w/cpp/language/lambda

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