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111
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1 // PR c++/59204
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2 // { dg-do compile { target c++11 } }
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3
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4 template< class T >
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5 using void_t = void;
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6
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7 template< class T, class = void >
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8 struct has_type
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9 { constexpr static bool value = false; };
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10
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11 template< class T >
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12 struct has_type<T, void_t<typename T::type>>
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13 { constexpr static bool value = true; };
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14
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15 struct yes { using type = int; };
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16 struct no { };
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17
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18 int
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19 main( )
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20 {
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21 static_assert( has_type<yes>::value, "false negative!" );
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22 static_assert( not has_type<no >::value, "false positive!" );
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23 }
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