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Comment by RcouF1uZ4gsC | Hacker News Reader

In C++ because of how it developed the defaults are not optimal. For example, constructors and conversions are implicit and you have to make them explicit. Variables are default mutable and you have to make them const. Local primitive variables are default unitialized by default.

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> Variables are default mutable and you have to make them const

Except for the captured variables in a lambda which are const unless you use the mutable keyword. Not a bad idea though.

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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