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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - declaring a template instance as friend makes all instances of the template as friend"
href="https://bugs.llvm.org/show_bug.cgi?id=40321">40321</a>
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<th>Summary</th>
<td>declaring a template instance as friend makes all instances of the template as friend
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>7.0
</td>
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<th>Hardware</th>
<td>All
</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>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C++
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>sw6ueyz@gmail.com
</td>
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=21329" name="attach_21329" title="the code">attachment 21329</a> <a href="attachment.cgi?id=21329&action=edit" title="the code">[details]</a></span>
the code
// this code should compile
// because 'Sub' declares only 'Wrapper< Good >' as friend.
template< class ... >
using Void_t = void;
template< class Key >
struct Wrapper
{
template< class To, class From, class Void = void >
struct IsCastable
{ static constexpr bool value = false; };
template< class To, class From >
struct IsCastable<
To, From, Void_t< decltype( static_cast< To >( From{} ) ) >
>
{ static constexpr bool value = true; };
};
struct Good {};
struct Bad {};
struct Base {};
struct Sub : private Base
{
friend struct Wrapper< Good >; // Wrapper< Good > is the only friend
};
int main()
{
// friendly access : should be true
static_assert(
Wrapper< Good >::IsCastable< Base*, Sub* >::value );
// non-friendly access : should be false
static_assert(
!Wrapper< Bad >::IsCastable< Base*, Sub* >::value );
return 0;
}</pre>
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