// bslmf_ispolymorphic.h -*-C++-*-
#ifndef INCLUDED_BSLMF_ISPOLYMORPHIC
#define INCLUDED_BSLMF_ISPOLYMORPHIC
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
//@PURPOSE: Provide a compile-time check for determining polymorphic types.
//
//@CLASSES:
// bsl::is_polymorphic: standard meta-function for detecting polymorphic types
// bsl::is_polymorphic_v: the result value of the meta-function
// bslmf::IsPolymorphic: meta-function for detecting polymorphic types
//
//@DESCRIPTION: This component defines two meta-functions,
// 'bsl::is_polymorphic' and 'BloombergLP::bslmf::IsPolymorphic' and a template
// variable 'bsl::is_polymorphic_v', that represents the result value of the
// 'bsl::is_polymorphic' meta-function. All of these meta-functions may be
// used to query whether a type is a polymorphic class as defined in the C++11
// standard [class.virtual]. A class is polymorphic if it has at least one
// virtual function. Note that the destructor of such a class should *always*
// be declared 'virtual'. Therefore, another definition of polymorphic is
// whether a class has a virtual destructor.
//
// 'bsl::is_polymorphic' has the same syntax as the 'is_polymorphic' template
// defined in the C++11 standard [meta.unary.prop], while
// 'bslmf::IsPolymorphic' was devised before 'is_polymorphic' was standardized.
// 'bsl::is_polymorphic' meets the requirements of the C++11 standard with two
// exceptions:
//
//: 1 The compilation will fail if the meta-function is used to evaluate a
//: 'union' type, unless one of the following compilers, which provide an
//: intrinsic operation to detect this specific trait, is used:
//: o gcc 4.3 or later
//: o Visual C++ 2008 or later
//:
//: 2 The meta-function will yield false positives, claiming non-polymorphic
//: types *are* polymorphic, for types using virtual inheritance. This case
//: is known to be handled *correctly* for the following compilers only:
//: o Compilers with intrinsic support, listed above
//: o IBM XLC
//
// The two meta-functions are functionally equivalent. The major difference
// between them is that the result for 'bsl::is_polymorphic' is indicated by
// the class member 'value', while the result for 'bslmf::IsPolymorphic' is
// indicated by the class member 'VALUE'. 'bsl::is_polymorphic' should be
// preferred over 'bslmf::IsPolymorphic', and in general, should be used by new
// components.
//
// Note that the template variable 'is_polymorphic_v' is defined in the C++17
// standard as an inline variable. If the current compiler supports the inline
// variable C++17 compiler feature, 'bsl::is_polymorphic_v' is defined as an
// 'inline constexpr bool' variable. Otherwise, if the compiler supports the
// variable templates C++14 compiler feature, 'bsl::is_polymorphic_v' is
// defined as a non-inline 'constexpr bool' variable. See
// 'BSLS_COMPILERFEATURES_SUPPORT_INLINE_VARIABLES' and
// 'BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES' macros in
// bsls_compilerfeatures component for details.
//
///Usage
///-----
// In this section we show intended use of this component.
//
///Example 1: Verify Polymorphic Types
///- - - - - - - - - - - - - - - - - -
// Suppose that we want to assert whether a particular type is a polymorphic
// type.
//
// First, we define two types in a non-polymorphic hierarchy, 'MyStruct' and
// 'MyDerivedStruct':
//..
// struct MyStruct {
// void nonvirtualMethod();
// };
// struct MyDerivedStruct : public MyStruct {
// };
//..
// Then, we define two types in a polymorphic hierarchy, 'MyClass' and
// 'MyDerivedClass':
//..
// class MyClass {
// public:
// MyClass();
// virtual ~MyClass(); // makes 'MyClass' polymorphic
// };
//
// class MyDerivedClass : public MyClass {
// public:
// MyDerivedClass();
// virtual ~MyDerivedClass();
// };
//..
// Now, assert that the two types in the non-polymorphic hierarchy are not
// polymorphic, and that the two types in the polymorphic hierarchy are
// polymorphic using 'bsl::is_polymorphic':
//..
// assert(false == bsl::is_polymorphic<MyStruct >::value);
// assert(false == bsl::is_polymorphic<MyStruct *>::value);
// assert(false == bsl::is_polymorphic<MyDerivedStruct& >::value);
// assert(false == bsl::is_polymorphic<MyDerivedStruct *>::value);
//
// assert(true == bsl::is_polymorphic< MyClass >::value);
// assert(false == bsl::is_polymorphic<const MyClass& >::value);
// assert(false == bsl::is_polymorphic< MyClass *>::value);
// assert(true == bsl::is_polymorphic<MyDerivedClass >::value);
// assert(false == bsl::is_polymorphic<MyDerivedClass& >::value);
// assert(false == bsl::is_polymorphic<MyDerivedClass *>::value);
//..
// Note that if the current compiler supports the variable templates C++14
// feature then we can re-write the snippet of code above using the
// 'bsl::is_polymorphic_v' variable as follows:
//..
//#ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
// assert(false == bsl::is_polymorphic_v<MyStruct >);
// assert(false == bsl::is_polymorphic_v<MyStruct *>);
// assert(false == bsl::is_polymorphic_v<MyDerivedStruct& >);
// assert(false == bsl::is_polymorphic_v<MyDerivedStruct *>);
//
// assert(true == bsl::is_polymorphic_v< MyClass >);
// assert(false == bsl::is_polymorphic_v<const MyClass& >);
// assert(false == bsl::is_polymorphic_v< MyClass *>);
// assert(true == bsl::is_polymorphic_v<MyDerivedClass >);
// assert(false == bsl::is_polymorphic_v<MyDerivedClass& >);
// assert(false == bsl::is_polymorphic_v<MyDerivedClass *>);
//#endif
//..
#include <bslscm_version.h>
#include <bslmf_integralconstant.h>
#include <bslmf_isclass.h>
#include <bslmf_removecv.h>
#include <bsls_compilerfeatures.h>
#include <bsls_exceptionutil.h>
#include <bsls_keyword.h>
#include <bsls_platform.h>
#if defined(BSLS_PLATFORM_CMP_CLANG) \
|| defined(BSLS_PLATFORM_CMP_GNU) \
|| defined(BSLS_PLATFORM_CMP_MSVC) \
|| (defined(BSLS_PLATFORM_CMP_SUN) && BSLS_PLATFORM_CMP_VERSION >= 0x5130)
# define BSLMF_ISPOLYMORPHIC_HAS_INTRINSIC
#endif
namespace BloombergLP {
namespace bslmf {
// ========================
// struct IsPolymorphic_Imp
// ========================
#if defined(BSLMF_ISPOLYMORPHIC_HAS_INTRINSIC)
// Use type traits intrinsic, where available, to give the correct answer for
// the tricky cases where existing ABIs prevent programmatic detection.
template <class t_TYPE>
struct IsPolymorphic_Imp {
enum { Value = __is_polymorphic(t_TYPE) };
};
#else
template <class t_TYPE, bool t_IS_CLASS = bsl::is_class<t_TYPE>::value>
struct IsPolymorphic_Imp {
// This 'struct' template provides a meta-function to determine whether the
// (template parameter) 't_TYPE' is a (non-cv-qualified) polymorphic type.
// This generic default template defines a static data member, 'Value',
// that is set to 'false'. A template specialization is provided (below)
// to handle the case where 't_TYPE' is a class type that may be
// polymorphic.
enum { Value = false };
};
template <class t_TYPE>
struct IsPolymorphic_Imp<t_TYPE, true> {
// This partial specialization of 'IsPolymorphic_Imp', for when the
// (template parameter) 't_TYPE' is a (non-cv-qualified) class type,
// provides a static data member, 'Value', that is set to 'true' if
// 't_TYPE' is polymorphic and 'false' otherwise.
struct IsPoly : public t_TYPE {
IsPoly();
virtual ~IsPoly() BSLS_NOTHROW_SPEC;
char dummy[256];
};
struct MaybePoly : public t_TYPE {
MaybePoly();
~MaybePoly() BSLS_NOTHROW_SPEC;
char dummy[256];
};
enum { Value = (sizeof(IsPoly) == sizeof(MaybePoly)) };
};
#endif
} // close package namespace
} // close enterprise namespace
namespace bsl {
template <class t_TYPE>
struct is_polymorphic
: integral_constant<bool,
BloombergLP::bslmf::IsPolymorphic_Imp<
typename remove_cv<t_TYPE>::type>::Value> {
// This 'struct' template implements the 'is_polymorphic' meta-function
// defined in the C++11 standard [meta.unary.prop] to determine if the
// (template parameter) 't_TYPE' is a (possibly cv-qualified) polymorphic
// type. This 'struct' derives from 'bsl::true_type' if the 't_TYPE' is a
// polymorphic type, and 'bsl::false_type' otherwise.
};
#ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
template <class t_TYPE>
BSLS_KEYWORD_INLINE_VARIABLE constexpr bool is_polymorphic_v =
is_polymorphic<t_TYPE>::value;
// This template variable represents the result value of the
// 'bsl::is_polymorphic' meta-function.
#endif
} // close namespace bsl
namespace BloombergLP {
namespace bslmf {
// ====================
// struct IsPolymorphic
// ====================
template <class t_TYPE>
struct IsPolymorphic : bsl::is_polymorphic<t_TYPE>::type {
// This 'struct' template implements a meta-function to determine if the
// (template parameter) 't_TYPE' is a (possibly cv-qualified) polymorphic
// type. This 'struct' derives from 'bsl::true_type' if the 't_TYPE' is a
// polymorphic type, and 'bsl::false_type' otherwise.
//
// Note that although this 'struct' is functionally equivalent to
// 'bsl::is_polymorphic', the use of 'bsl::is_polymorphic' should be
// preferred.
};
} // close package namespace
#ifndef BDE_OPENSOURCE_PUBLICATION // BACKWARD_COMPATIBILITY
// ============================================================================
// BACKWARD COMPATIBILITY
// ============================================================================
#ifdef bslmf_IsPolymorphic
#undef bslmf_IsPolymorphic
#endif
#define bslmf_IsPolymorphic bslmf::IsPolymorphic
// This alias is defined for backward compatibility.
#endif // BDE_OPENSOURCE_PUBLICATION -- BACKWARD_COMPATIBILITY
} // close enterprise namespace
#endif
// ----------------------------------------------------------------------------
// Copyright 2013 Bloomberg Finance L.P.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ----------------------------- END-OF-FILE ----------------------------------