[LLVMbugs] [Bug 10442] New: Class with defaulted default constructor is not trivial

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Fri Jul 22 09:53:21 PDT 2011


           Summary: Class with defaulted default constructor is not
           Product: clang
           Version: trunk
          Platform: Macintosh
        OS/Version: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++0x
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: jonathan.sauer at gmx.de
                CC: llvmbugs at cs.uiuc.edu, dgregor at apple.com

The following program does not compile with clang r:

struct type
  type() = default; // trivial

static_assert(__is_trivial(type), "Not trivial");

This results in:

clang -std=c++0x clang.cpp clang.cpp:5:1: error: static_assert failed "Not
static_assert(__is_trivial(Foo), "Not trivial");
^             ~~~~~~~~~~~~~~~~~
1 error generated.

This is contrary to N2210 (where this example is excerpted from), that states
that a defaulted default constructor is trivial if inline:

| Critical to exploiting the benefits of  N2172, an inline and explicitly
defaulted definition is trivial if and
| only if the implicit definition would have been trivial. The potential
concern with out-of-class definition
| is "How is the compiler to know if it is trivial?". The existing rule that an
inline definition must occur
| before any use suffices here as well.

C.f. FDIS 12.1p5:

| A default constructor is trivial if it is not user-provided and if [nothing
that applies here]

(I don't think a defaulted default constructor should count as "user-provided")

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