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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - constexpr function ill-formed but error message incorrect"
href="http://llvm.org/bugs/show_bug.cgi?id=18874">18874</a>
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<th>Summary</th>
<td>constexpr function ill-formed but error message incorrect
</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>Other
</td>
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<th>OS</th>
<td>other
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C++1y
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>yaghmour.shafik@gmail.com
</td>
</tr>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>In the following program:
#include <cstddef>
template <typename T, size_t s>
struct test
{
T x[s] ;
} ;
template <typename T>
constexpr T func() {
test<T,3> test1 ;
test1.x[0] = 10 ;
return test1.x[0];
}
constexpr int func2() {
test<int,3> test1 ;
test1.x[0] = 10 ;
return test1.x[0];
}
int main()
{
constexpr int x = func<int>();
}
func and func2 should be ill-formed for the same reason that variable test1 is
not initialized nor does it have a constexpr constructor but in func the error
message is:
main.cpp:13:11: note: assignment to object outside its lifetime is not
allowed in a constant expression
test1.x[0] = 10 ;
^
which does not make any sense since test1 should be trivial and it's lifetime
should begin with it's declaration and extend over the whole function.
I would expect an error similar to the one we see for func2 which is as
follows:
main.cpp:20:14: note: non-constexpr constructor 'test' cannot be used in a
constant expression
test<int,3> test1 ;
^
I am building using the following command line:
clang++ -std=c++1y -O0 -Wall -Wextra -Wconversion -pedantic
You can see this on Coliru here:
<a href="http://coliru.stacked-crooked.com/a/16ed43ed478fbc55">http://coliru.stacked-crooked.com/a/16ed43ed478fbc55</a>
This was originally brought up in this StackOverflow question:
<a href="http://stackoverflow.com/questions/21806154/c1y-c14-assignment-to-object-outside-its-lifetime-is-not-allowed-in-a-const">http://stackoverflow.com/questions/21806154/c1y-c14-assignment-to-object-outside-its-lifetime-is-not-allowed-in-a-const</a>
This does not seem like a major bug but the error message sure is confusing.</pre>
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