Path: utzoo!attcan!ncrcan!hcr!ron
From: ron@hcr.UUCP (Ron Irvine)
Newsgroups: comp.lang.c++
Subject: scope of FOR
Message-ID: <1807@hcr.UUCP>
Date: 21 Aug 89 18:59:16 GMT
Reply-To: ron@hcrvx1.UUCP (Ron Irvine)
Organization: HCR Corporation, Toronto
Lines: 40

The expansion of the FOR statement in C++ is great.
Being able to say "for(int i=0; i<100; ++i) ... " is
just what I want when I am coding a loop.  However, I
could not believe that C++ has defined the scope of the
declared name (i in this case) to be "to the end of the
block enclosing the for-statement" (pg. 294, of The C++
programming language).

One problem with the current definition is that it
reduces the possibility of optimizations since the
variable may be used after the for statement.
It also makes the job of detecting simple loops
much harder since the declared variable must be tracked
until the end of the enclosing scope. This in turn makes
it less likely that a machine looping instruction will
be generated by the compiler.

The other problem is that it does not fit with the data
hiding philosophy of C++.  The for statement:

	for (statement-1 expression-1 ; expression-2)
		statement-2

should be redefined to be the equivalent of the following
COMPOUND statement:

	{	/* <-- note the enclosing scope */
		statement-1
		while (expression-1) {
			statement-2
			expression-2;
		}
	}

This would let programmers localize the extent of the declared
variable to the FOR statement.  Bjarne could you please fix this.


Cycles for nothing,		|   Ron Irvine, HCR
Mips for free.