🚀 go-pugleaf

In article <1992Nov2.162310.10094@ichips.intel.com>, bhoughto@sedona.intel.com (Blair P. Houghton) writes:
> First, Jutta Degener and I are having a discussion on the
> Standard's use of the verb "to use" in the context of
> value contexts.

As in 3.2.2.2 where it says:

	The (nonexistent) value of a void expression (an expression
	that has type void) shall not be used in any way...

or is there some other use of "to use" that I don't remember.

> I'm trying to develop a good definition, and it's come
> down to a few expression forms.  The important
> thing to remember is that it's the value, not the
> identifier or the location, that is being "used."
> 
> 	if ( foo ) ...;		/* uses `foo' */
> 	foo;			/* does not use `foo' */
> 	x = foo;		/* uses `foo' */
> 	foo = x;		/* does not use `foo' */

I agree, but I think it's much clearer to say *value* of `foo' rather
than just `foo'.

> I'd say it was merely a matter of whether a side-effect
> depends on the value, but `if ( foo ) /* empty */;' does not
> have any side effects, but definitely does use the value
> of `foo'.  (Remember, "issues of optimization are
> irrelevant," so the null statement WILL be "executed"
> in the "abstract machine.")

I think side-effects are a red herring.  What's important is whether
the value is *used* or not; the semantics in 3.3 Expressions and
3.6 Statements (and possible other subsections) specify where values
are used.

> 	"A string literal is a primary expression.
> 	 It is an lvalue..."
> 			 (ANSI X3.159-1989, sec. 3.3.1
> 			 Primary Expressions, p. 40, l. 13)
> 
> It's an LVALUE.  This means that,
> 
> 	"foo" = "bar";
> 
> is legal.  Right?

Nope.  Remember that the Standard distinguishes between lvalues and
modifiable lvalues.  "foo" is an lvalue -- it identifies an object --
but it's an array type and thus is *not* a modifiable lvalue.  If it
wasn't a lvalue you couldn't take it's address!
----
Larry Jones, SDRC, 2000 Eastman Dr., Milford, OH  45150-2789  513-576-2070
larry.jones@sdrc.com  or  ...uunet!sdrc!larry.jones
I've changed my mind, Hobbes.  People are scum. -- Calvin