If a closure cannot be optimized out, i.e. the scope of the closure outlives the scope of the function it captures a variable from, than this closure is equival

If a closure cannot be optimized out, i.e. the scope of the closure outlives the scope of the function it captures a variable from, than this closure is equivalent to a heap allocated struct, which cannot be allocated on the stack either if it outlives its scope. So the cost is still the same.