abstract1.c

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// { dg-do compile }
// Contributed by <giovannibajo at gcc dot gnu dot org>,
//                <pavel_vozenilek at hotmail dot com>,
//                <bangerth at dealii dot org>
// c++/9256: Make sure that a pointer to an array of abstract elements
//  cannot be created, not even during template substitution (DR337).

struct Abstract { virtual void f() = 0; };  // { dg-error "" } 
struct Complete { void f(); };


/*
 * TEST 1
 * Arrays of abstract elements cannot be declared.
 */

Abstract a0[2];        // { dg-error "" }
Abstract (*a1)[2];     // { dg-error "" }
Abstract (**a2)[2];    // { dg-error "" }
Abstract (***a3)[2];   // { dg-error "" }
Abstract *a4;
Abstract *a5[2];
Abstract (*a6[2])[2];  // { dg-error "" }
Abstract **a7[2];
Abstract *(*a8[2])[2];  
Abstract (**a9[2])[2]; // { dg-error "" }

/*
 * TEST 2
 * If a pointer to an array of abstract elements is created during template
 *  instantiation, an error should occur.
 */

template <class T> struct K {
  T (*a)[2];   // { dg-error "abstract class type" }
};

template struct K<Abstract>;  // { dg-error "from here" }



/*
 * TEST 3
 * Deducing an array of abstract elements during type deduction is a silent
 *  failure (rejects overload).
 */

template <bool> struct StaticAssert;
template <> struct StaticAssert<true> {};

typedef char Yes;
typedef struct { char x[2]; } No;

template<typename U> No  is_abstract(U (*k)[1]);
template<typename U> Yes is_abstract(...);

StaticAssert<sizeof(is_abstract<Abstract>(0)) == sizeof(Yes)> b1;
StaticAssert<sizeof(is_abstract<Complete>(0)) == sizeof(No)> b2;
StaticAssert<sizeof(is_abstract<int>(0)) == sizeof(No)> b3;