[boost] [optional] References

From: Roman Odaisky (roma_at_[hidden])
Date: 2008-06-01 14:42:18

Greetings,

boost::optional<T &> seems to be implemented in terms of a boolean flag and an 
aligned_storage. Wouldn’t it make more sense to make boost::optional<T &> a 
thin wrapper over T*? This would save a couple of bytes, speed up get_ptr by 
a couple of ticks, and perhaps reduce compilation times.

Also, from the documentation[1]:

> Rebinding semantics for the assignment of initialized  optional references 
has been chosen to provide consistency among initialization states  even at 
the expense of lack of consistency with the semantics of bare C++ references. 
It is true that optional<U> strives to behave as much as possible as U  does 
whenever it is initialized; but in the case when U  is T&, doing so would 
result in inconsistent behavior w.r.t to the lvalue initialization state.

optional<U> does not have the semantics of U, but rather those of U*. That 
explains the assignment semantics perfectly well:

int a = 1;
int b = 2;

int& ra = a;
int& rb = b;

int* pa = &a;
int* pb = &b;

boost::optional<int &> oa(ra);
boost::optional<int &> ob(rb);

ra = rb; // assigns b to a
pa = pb; // rebinds pa to b
oa = ob; // rebinds oa to b

-- 
[1] http://tinyurl.com/55s8f7
-- 
WBR
Roman.