Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!snorkelwacker!mit-eddie!uw-beaver!uw-entropy!dataio!bright
From: bright@Data-IO.COM (Walter Bright)
Newsgroups: comp.lang.c++
Subject: Re: Why doesn't inline always work?
Keywords: inline fails
Message-ID: <2370@dataio.Data-IO.COM>
Date: 9 Mar 90 19:17:44 GMT
References: <540@janus.Quotron.com>
Reply-To: bright@Data-IO.COM (Walter Bright)
Organization: Data I/O Corporation; Redmond, WA
Lines: 33

In article <540@janus.Quotron.com> todd@janus.Quotron.com (Todd Booth) writes:
<I know of a 2.0 C++ beta product that does not expand inline
<functions that contain a goto, for, do, or while, as inline.  
<Do any other C++ products?
	No.
<Can anyone think of a technical reason not to (assuming the
<programmer knows what s/he is doing?

Because of the following circumstance:

	inline int func()
	{	int i;
		for (i = 0; i < 10; i++)
			g();
		return i;
	}

Now, suppose it appears in:

	foo(a || (c += (g(),func()) + g()) || baz);

Try to inline-expand this, preserving the semantics.

C++ compilers inline-expand functions by substituting expressions.
for, switch, while etc. do not map into C expressions.
If's can usually be converted into an equivalent C expression
using &&, || or ?:.

Some significant gymnastics would be required to solve this problem
in the general case, and most implementors (I presume) feel that the
gain to the user is not worth the implementation effort, complexity
and bugs. There's a long list of other things that have higher
priority (such as more efficient code generation).