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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Clang 5.0 consider template method unevaluated and accepts this code, GCC rejects it"
href="https://bugs.llvm.org/show_bug.cgi?id=34009">34009</a>
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<th>Summary</th>
<td>Clang 5.0 consider template method unevaluated and accepts this code, GCC rejects it
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C++11
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
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<th>Reporter</th>
<td>joker.eph@gmail.com
</td>
</tr>
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<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org
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<p>
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<pre>Clang accepts the following (C++11) code while GCC rejects it (4.9 to 7.0).
Clang seems to consider that the constexpr `IS_N` is enough to make the method
`bar()` unevaluated, while gcc complains. I don't understand what makes clang
happy here?
Changing the define makes both compiler happy, as the constexpr is dependent on
the template args.
#include <type_traits>
#define INDEPENDENT_CONSTEXPR 1
template<int N = 1>
struct Bar {
typename std::enable_if<N != 1, void>::type foo() {
}
};
template<int N = 1>
struct Foo {
#if INDEPENDENT_CONSTEXPR
static constexpr bool IS_N = true;
#else
static constexpr bool IS_N = (N == 1);
#endif
// (N == 1);
using myBar = Bar<IS_N>;
void bar() {
myBar b;
b.foo();
}
};
void foobar() {
Foo<0> f0;
Foo<1> f1;
#if !INDEPENDENT_CONSTEXPR
f0.bar();
#endif
// Following should never work
// f1.bar();
}</pre>
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