<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">Can you give a motivating example from WebKit?<div><br></div><div>Geoff</div><div><br><div><div>On Apr 19, 2014, at 1:09 PM, Filip Pizlo <<a href="mailto:fpizlo@apple.com">fpizlo@apple.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div style="font-family: Helvetica, Arial; font-size: 13px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;">Hey everyone,</div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;"><br></div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;">When guarding code with macros that are always defined, such as ASSERT_DISABLED (it's always either 0 or 1), we have a choice between:</div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;"><br></div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;"><span class="Apple-tab-span" style="white-space: pre;"> </span>if (!ASSERT_DISABLED) {</div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;"><span class="Apple-tab-span" style="white-space: pre;"> </span> // do things</div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;"><span class="Apple-tab-span" style="white-space: pre;"> </span>}</div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;"><br></div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;">and:</div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;"><br></div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;">#if !ASSERT_DISABLED</div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;"><span class="Apple-tab-span" style="white-space: pre;"> </span>// do things</div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;">#endif</div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;"><br></div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;">I'd like to propose that<span class="Apple-converted-space"> </span><i>anytime the normal if would be semantically equivalent to the preprocessor #if, the normal if should be used</i>.</div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;"><br></div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;">We don't lose any compiler optimization, since even at -O0, the compiler will constant fold the normal if. We do gain a lot of clarity, since the control flow of normal if statements is subject to proper indentation.</div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;"><br></div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;">The "semantically equivalent" requirement still allows for #if to be used for thinngs like:</div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;"><br></div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;">- Guarding the placement of fields in a class.</div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;">- Guarding the definitions of other macros (in the case of ASSERT_DISABLED, we define ASSERT in different ways guarded by #if's)</div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;">- Guarding the definition/declaration/inclusion of entire functions, classes, and other top-level constructs.</div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;"><br></div><div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; margin: 0px;">Thoughts?</div><br><div id="bloop_sign_1397937780250571008" class="bloop_sign"><div style="font-family: helvetica, arial; font-size: 13px;">-Phil</div><div style="font-family: helvetica, arial; font-size: 13px;"><br></div></div>_______________________________________________<br>webkit-dev mailing list<br><a href="mailto:webkit-dev@lists.webkit.org">webkit-dev@lists.webkit.org</a><br><a href="https://lists.webkit.org/mailman/listinfo/webkit-dev">https://lists.webkit.org/mailman/listinfo/webkit-dev</a></div></blockquote></div><br></div></body></html>