Source/WTF/wtf/Forward.h

/*
 *  Copyright (C) 2006-2018 Apple Inc. All rights reserved.
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Library General Public
 *  License as published by the Free Software Foundation; either
 *  version 2 of the License, or (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  Library General Public License for more details.
 *
 *  You should have received a copy of the GNU Library General Public License
 *  along with this library; see the file COPYING.LIB.  If not, write to
 *  the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 *  Boston, MA 02110-1301, USA.
 *
 */

#pragma once

#include <stddef.h>

namespace std {
template<typename T> class optional;
}

namespace WTF {

class AtomicString;
class AtomicStringImpl;
class BinarySemaphore;
class CString;
class CrashOnOverflow;
class FunctionDispatcher;
class Hasher;
class MonotonicTime;
class OrdinalNumber;
class PrintStream;
class SHA1;
class Seconds;
class String;
class StringBuilder;
class StringImpl;
class StringView;
class TextPosition;
class TextStream;
class UniquedStringImpl;
class WallTime;

struct FastMalloc;

template<typename> class CompletionHandler;
template<typename T> struct DumbPtrTraits;
template<typename T> struct DumbValueTraits;
template<typename> class Function;
template<typename> class LazyNeverDestroyed;
template<typename> class NeverDestroyed;
template<typename> class OptionSet;
template<typename T, typename = DumbPtrTraits<T>> class Ref;
template<typename T, typename = DumbPtrTraits<T>> class RefPtr;
template<typename> class StringBuffer;
template<typename, typename = void> class StringTypeAdapter;

template<typename> struct DefaultHash { using Hash = void; };
template<typename> struct HashTraits;

template<typename...> class Variant;
template<typename, size_t = 0, typename = CrashOnOverflow, size_t = 16, typename = FastMalloc> class Vector;
template<typename Value, typename = typename DefaultHash<Value>::Hash, typename = HashTraits<Value>> class HashCountedSet;
template<typename KeyArg, typename MappedArg, typename = typename DefaultHash<KeyArg>::Hash, typename = HashTraits<KeyArg>, typename = HashTraits<MappedArg>> class HashMap;
template<typename ValueArg, typename = typename DefaultHash<ValueArg>::Hash, typename = HashTraits<ValueArg>> class HashSet;

}

namespace std {
namespace experimental {
inline namespace fundamentals_v3 {
template<class, class> class expected;
template<class> class unexpected;
}}} // namespace std::experimental::fundamentals_v3

using WTF::AtomicString;
using WTF::AtomicStringImpl;
using WTF::BinarySemaphore;
using WTF::CString;
using WTF::CompletionHandler;
using WTF::DumbPtrTraits;
using WTF::DumbValueTraits;
using WTF::Function;
using WTF::FunctionDispatcher;
using WTF::HashCountedSet;
using WTF::HashMap;
using WTF::HashSet;
using WTF::Hasher;
using WTF::LazyNeverDestroyed;
using WTF::NeverDestroyed;
using WTF::OptionSet;
using WTF::OrdinalNumber;
using WTF::PrintStream;
using WTF::Ref;
using WTF::RefPtr;
using WTF::SHA1;
using WTF::String;
using WTF::StringBuffer;
using WTF::StringBuilder;
using WTF::StringImpl;
using WTF::StringView;
using WTF::TextPosition;
using WTF::TextStream;
using WTF::Variant;
using WTF::Vector;

template<class T, class E> using Expected = std::experimental::expected<T, E>;
template<class E> using Unexpected = std::experimental::unexpected<E>;

// Sometimes an inline method simply forwards to another one and does nothing else. If it were
// just a forward declaration of that method then you would only need a forward declaration of
// its return types and parameter types too, but because it's inline and it actually needs to
// return / pass these types (even though it's just passing through whatever it called) you
// now find yourself having to actually have a full declaration of these types. That might be
// an include you'd rather avoid.
//
// No more. Enter template magic to lazily instantiate that method!
//
// This macro makes the method work as if you'd declared the return / parameter types as normal,
// but forces lazy instantiation of the method at the call site, at which point the caller (not
// the declaration) had better have a full declaration of the return / parameter types.
//
// Simply pass the forward-declared types to the macro, with an alias for each, and then define
// your function as you otherwise would have but using the aliased name. Why the alias? So you
// can be lazy on templated types! Sample usage:
//
// struct Foo; // No need to define Foo!
// template<typename T>
// struct A {
//     Foo declared(Bar); // Forward declarations of Foo and Bar are sufficient here.
//     // The below code would normally require a definition of Foo and Bar.
//     WTF_LAZY_INSTANTIATE(Foo=Foo, Bar=Bar) Foo forwarder(Bar b) { return declared(b); }
// };
#define WTF_LAZY_JOIN_UNLAZE(A, B) A##B
#define WTF_LAZY_JOIN(A, B) WTF_LAZY_JOIN_UNLAZE(A, B)
#define WTF_LAZY_ARGUMENT_NUMBER(_1, _2, _3, _4, _5, _6, _7, N, ...) N
#define WTF_LAZY_REVERSE_SEQUENCE() 7, 6, 5, 4, 3, 2, 1, 0
#define WTF_LAZY_NUM_ARGS_(...) WTF_LAZY_ARGUMENT_NUMBER(__VA_ARGS__)
#define WTF_LAZY_NUM_ARGS(...) WTF_LAZY_NUM_ARGS_(__VA_ARGS__, WTF_LAZY_REVERSE_SEQUENCE())
#define WTF_LAZY_FOR_EACH_TERM(F, ...) \
    WTF_LAZY_JOIN(WTF_LAZY_FOR_EACH_TERM_, WTF_LAZY_NUM_ARGS(__VA_ARGS__))(F, (__VA_ARGS__))
#define WTF_LAZY_FIRST(_1, ...) _1
#define WTF_LAZY_REST(_1, ...) (__VA_ARGS__)
#define WTF_LAZY_FOR_EACH_TERM_0(...)
#define WTF_LAZY_FOR_EACH_TERM_1(F, ARGS) F(WTF_LAZY_FIRST ARGS) WTF_LAZY_FOR_EACH_TERM_0(F, WTF_LAZY_REST ARGS)
#define WTF_LAZY_FOR_EACH_TERM_2(F, ARGS) F(WTF_LAZY_FIRST ARGS) WTF_LAZY_FOR_EACH_TERM_1(F, WTF_LAZY_REST ARGS)
#define WTF_LAZY_FOR_EACH_TERM_3(F, ARGS) F(WTF_LAZY_FIRST ARGS) WTF_LAZY_FOR_EACH_TERM_2(F, WTF_LAZY_REST ARGS)
#define WTF_LAZY_FOR_EACH_TERM_4(F, ARGS) F(WTF_LAZY_FIRST ARGS) WTF_LAZY_FOR_EACH_TERM_3(F, WTF_LAZY_REST ARGS)
#define WTF_LAZY_FOR_EACH_TERM_5(F, ARGS) F(WTF_LAZY_FIRST ARGS) WTF_LAZY_FOR_EACH_TERM_4(F, WTF_LAZY_REST ARGS)
#define WTF_LAZY_FOR_EACH_TERM_6(F, ARGS) F(WTF_LAZY_FIRST ARGS) WTF_LAZY_FOR_EACH_TERM_5(F, WTF_LAZY_REST ARGS)
#define WTF_LAZY_FOR_EACH_TERM_7(F, ARGS) F(WTF_LAZY_FIRST ARGS) WTF_LAZY_FOR_EACH_TERM_6(F, WTF_LAZY_REST ARGS)
#define WTF_LAZY_DECLARE_ALIAS_AND_TYPE(ALIAS_AND_TYPE) typename ALIAS_AND_TYPE,
#define WTF_LAZY_INSTANTIATE(...)                                        \
    template<                                                            \
    WTF_LAZY_FOR_EACH_TERM(WTF_LAZY_DECLARE_ALIAS_AND_TYPE, __VA_ARGS__) \
    typename = void>