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From: phalpern@truffle.ma.ultranet.com (Pablo Halpern)
Subject: Re: string/cow/algorithm
Date: 1998/08/21
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AllanW@my-dejanews.com wrote:

>Of course, whenever the user gets a reference or address of a
>character in the string -- no matter how (operator[], or dereferencing
>an iterator) -- taking and holding the address is an absolute no-no.
>This isn't just for ref-counted strings, but also for any other
>container that moves things without an explicit request to do so
>(such as vector).

Not quite right.  There are specific operations that invalidate
references to elements.  Copying the container is not one of them. That
is why operator[] (and begin() and end()) must mark the buffer as
unshareable. Otherwise, a copy of the container could be modified
through a (still valid) element reference that was taken before the copy
was made:

	string A("hello world");
	char& r = A[3];   // get and hold a reference to 4th char
	string B(A);      // B had better not share a buffer with A!
	                  // r is still a valid reference.
	r = 'n';	  // Should modify A[3] but not B[3]


-------------------------------------------------------------
Pablo Halpern                   phalpern@truffle.ultranet.com

I am self-employed. Therefore, my opinions *do* represent 
those of my employer.


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