Re: [boost] [local] Help for the Alternatives section

Subject: Re: [boost] [local] Help for the Alternatives section
From: lcaminiti (lorcaminiti_at_[hidden])
Date: 2011-05-12 16:16:25

Jeffrey Lee Hellrung, Jr.-2 wrote:
> 
> I meant to explicitly ask whether the following are equivalent:
> 
>     bind(T)& x
>     bind(T&) x
> 
> [...]
> 

No, they are not.

bind(T)& x binds by reference so a change to x within the local scope will
reflect to x in the enclosing scope.
bind(T&) x binds by value so a change to x within the local scope will /not/
reflect to x in the enclosing scope.

int x = 0;
int& r = x;
int y = 0;
int& s = y;

BOOST_LOCAL_BLOCK(bind(int&) r, bind(int&)& s) { // Only s bind by ref.
    r = -1; // Does not affect enclosing scope.
    s = -1; // Affects enclosing scope.
} BOOST_LOCAL_BLOCK_END

assert(r == 0); // Not changed by local block.
assert(s == -1); // Changed by local block.

In bind(T&)& the outer reference is the one that applies to the variable
binding. The inner reference only indicates what the original variable type
is.

--Lorenzo

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