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Re: [cxx-abi-dev] C++0x: Mangling of decltype

  • To: cxx-abi-dev@xxxxxxxxxxxxxxxx
  • Subject: Re: [cxx-abi-dev] C++0x: Mangling of decltype
  • From: Daveed Vandevoorde <daveed@xxxxxxx>
  • Date: Wed, 11 Jul 2007 10:03:40 -0400

On Jul 11, 2007, at 9:35 AM, Doug Gregor wrote:


Continuing the string of manglings for C++0x, I propose the following
mangling schemes for decltype. decltype is like "typeof", and is
described here:

 http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2115.pdf

There are two mangling rules:

 <type> ::= Dt <expression> E  # decltype of an id-expression or
class member access (C++0x)
            ::= DT <expression> E  # decltype of an expression (C++0x)

We need two rules because decltype behaves differently for
id-expressions and class member accesses vs. full expressions. For
example:

 int x;
 decltype(x) y1; // y1 has type "int"
 decltype((x)) y2; // y2 has type "int &"

A patch to the ABI document is below.



The codes look good.
However, I don't think those type entries belong in the "qualifiers section". Instead, I'd introduce a new paragraph somewhere after the introduction of <expression>.
Also (and this is about the previous patch introducing "Dp"), I'd prefer the "U" entry (vendor extension) to remain the last in the list. I.e., swap the Dp and U codes. 

Ah, and another note regarding your previous patch: I'd change
	C++0x pack expansions are qualified with <code>Dp</code>.
to
	C++0x pack expansions are prefixed with <code>Dp</code>.


Thanks,

	Daveed



 - Doug

diff -u orig/abi-mangling.html ./abi-mangling.html
--- orig/abi-mangling.html	2007-07-11 09:21:46.000000000 -0400
+++ ./abi-mangling.html	2007-07-11 09:28:02.000000000 -0400
@@ -50,6 +50,8 @@
<tr><td>oper</td> <td>d</td> <td> v </td> <td> Operator / </td> </tr>
<tr><td>oper</td> <td>d</td> <td> V </td> <td> Operator /= </td> </tr>
<tr><td>type</td> <td>D</td> <td> p </td> <td> pack expansion of
(C++0x) </td> </tr>
+<tr><td>type</td> <td>D</td> <td> t </td> <td> decltype of an
id-expression or class member access (C++0x) </td> </tr>
+<tr><td>type</td> <td>D</td> <td> T </td> <td> decltype of an
expression (C++0x) </td> </tr>
<tr><td>obj </td> <td>D</td> <td> 0 </td> <td> Deleting destructor</ td> </tr> 
<tr><td>obj </td> <td>D</td> <td> 1 </td> <td> Complete object
(in-charge) destructor</td> </tr>
<tr><td>obj </td> <td>D</td> <td> 2 </td> <td> Base object
(not-in-charge) destructor</td> </tr>
diff -u orig/abi.html ./abi.html
--- orig/abi.html	2007-07-11 09:21:41.000000000 -0400
+++ ./abi.html	2007-07-11 09:27:23.000000000 -0400
@@ -4156,6 +4156,8 @@
	 ::= G &lt;type&gt;	# imaginary (C 2000)
::= U &lt;source-name&gt; &lt;type&gt; # vendor extended type qualifier 
         ::= Dp &lt;type&gt;  # pack expansion of (C++0x)
+         ::= Dt &lt;expression&gt; E  # decltype of an id-expression
or class member access (C++0x)
+ ::= DT &lt;expression&gt; E # decltype of an expression (C++0x) &lt;CV-qualifiers&gt; ::= [r] [V] [K] # restrict (C99), volatile, const 

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