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Thanks Richard and David for your replies. That was helpful.</div>
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Regards,</div>
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Manu</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Richard Smith <richard@metafoo.co.uk><br>
<b>Sent:</b> Sunday, August 23, 2020 11:56 PM<br>
<b>To:</b> Manu agarwal <Manu.Agarwal@live.in><br>
<b>Cc:</b> cfe-users@lists.llvm.org <cfe-users@lists.llvm.org><br>
<b>Subject:</b> Re: [cfe-users] inconsistent compilation error inside constexpr if</font>
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<div dir="ltr">On Fri, 21 Aug 2020 at 13:29, Manu agarwal via cfe-users <<a href="mailto:cfe-users@lists.llvm.org">cfe-users@lists.llvm.org</a>> wrote:<br>
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Hello,</div>
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In the below code the compiler throws "undeclared identifier" when the commented line is uncommented. Whereas the line just before compiles fine.</div>
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Regards,</div>
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Manu</div>
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<div>typedef bool (* DummyFunc) ();</div>
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<div>bool ExecDummy (DummyFunc fptr) {</div>
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<div> if (fptr)</div>
<div> return fptr ();</div>
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<div> return false;</div>
<div>}</div>
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<div>constexpr unsigned int IsMyAppClient = 0;</div>
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<div>constexpr bool CheckForTypeClient (unsigned int pAppType)</div>
<div>{</div>
<div> return ((pAppType & IsMyAppClient) != 0);</div>
<div>}</div>
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<div>class MyAppTemplate</div>
<div>{</div>
<div>public:</div>
<div> template <unsigned int T></div>
<div> static bool MyAppInit ();</div>
<div>};</div>
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<div>template <unsigned int T></div>
<div>bool</div>
<div>MyAppTemplate::MyAppInit ()</div>
<div>{</div>
<div> if constexpr (CheckForTypeClient(T)) {</div>
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<div><b> return ClientMain (); // no error</b></div>
<div><b> //return ExecDummy(ClientMain); // error: use of undeclared identifier 'ClientMain'</b></div>
<div> }</div>
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<div>This code is invalid, as David Blaikie explains. However, in MSVC-compatible mode (under -fms-compatibility, which is enabled by default for some Windows-targeting modes), Clang attempts to to accept certain invalid code that MSVC has historically accepted,
including this case, where we allow the call to ClientMain() to find declarations of a ClientMain function that appear after the template definition. That recovery from invalid code is only done for certain syntactic patterns, such as unqualified function
calls -- so it applies to ClientMain() but not to (ClientMain).</div>
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<div> return false;</div>
<div>}</div>
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<div>int __cdecl</div>
<div>main (int pArgc, char* pArgv[])</div>
<div>{</div>
<div> constexpr int TVal = 3;</div>
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<div> MyAppTemplate::MyAppInit<TVal> ();</div>
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<div> return 0;</div>
<div>}</div>
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