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Comment by Maxatar | Hacker News Reader

And that's only true if you capture by value. If you capture by reference they remain mutable.

I think this is because `mutable` qualifies the call operator of the lambda (like a reverse const qualifier) so by-value captures are effectively const during the call unless the lambda is marked `mutable`. References themselves are always const, but the referenced object may be modified through the reference depending on its constness even though the lambda is not `mutable`.

Is there a way to force capture by const-reference by the way?

  int main() {
     int x = 0;
     [&x] { x= 1;}(); // works
     [&x=std::as_const(x)] { x= 1;}(); // error: assignment of read-only reference 'x'
   }

Not very pretty, but it works.

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