Move talk/session/media -> webrtc/pc

talk/session/media/typewrapping.h.pump

-// To generate typewrapping.h from typewrapping.h.pump, execute:
-// /home/build/google3/third_party/gtest/scripts/pump.py typewrapping.h.pump
-
-// Copyright 2009 Google Inc.
-// Author: tschmelcher@google.com (Tristan Schmelcher)
-//
-// A template meta-programming framework for customizable rule-based
-// type-checking of type wrappers and wrapper functions.
-//
-// This framework is useful in a scenario where there are a set of types that
-// you choose to "wrap" by implementing new preferred types such that the new
-// and the old can be converted back and forth in some way, but you already have
-// a library of functions that expect the original types. Example:
-//
-// Type A wraps X
-// Type B wraps Y
-// Type C wraps Z
-//
-// And function X Foo(Y, Z) exists.
-//
-// Since A, B, and C are preferred, you choose to implement a wrapper function
-// with this interface:
-//
-// A Foo2(B, C)
-//
-// However, this can lead to subtle discrepancies, because if the interface to
-// Foo ever changes then Foo2 may become out-of-sync. e.g., Foo might have
-// originally returned void, but later is changed to return an error code. If
-// the programmer forgets to change Foo2, the code will probably still work, but
-// with an implicit cast to void inserted by the compiler, potentially leading
-// to run-time errors or errors in usage.
-//
-// The purpose of this library is to prevent these discrepancies from occurring.
-// You use it as follows:
-//
-// First, declare a new wrapping ruleset:
-//
-// DECLARE_WRAPPING_RULESET(ruleset_name)
-//
-// Then declare rules on what types wrap which other types and how to convert
-// them:
-//
-// DECLARE_WRAPPER(ruleset_name, A, X, variable_name, wrapping_code,
-//     unwrapping_code)
-//
-// Where wrapping_code and unwrapping_code are expressions giving the code to
-// use to wrap and unwrap a variable with the name "variable_name". There are
-// also some helper macros to declare common wrapping schemes.
-//
-// Then implement your wrapped functions like this:
-//
-// A Foo_Wrapped(B b, C c) {
-//   return WRAP_CALL2(ruleset_name, A, Foo, B, b, C, c);
-// }
-//
-// WRAP_CALL2 will unwrap b and c (if B and C are wrapped types) and call Foo,
-// then wrap the result to type A if different from the return type. More
-// importantly, if the types in Foo's interface do not _exactly_ match the
-// unwrapped forms of A, B, and C (after typedef-equivalence), then you will get
-// a compile-time error for a static_cast from the real function type to the
-// expected one (except on Mac where this check is infeasible), and with no icky
-// template instantiation errors either!
-//
-// There are also macros to wrap/unwrap individual values according to whichever
-// rule applies to their types:
-//
-// WRAP(ruleset_name, A, X, value) // Compile-time error if no associated rule.
-//
-// UNWRAP(ruleset_name, A, value) // Infers X. If A is not a wrapper, no change.
-//
-// UNWRAP_TYPE(ruleset_name, A) // Evaluates to X.
-//
-//
-// Essentially, the library works by "storing" the DECLARE_WRAPPER calls in
-// template specializations. When the wrapper or unwrapper is invoked, the
-// normal C++ template system essentially "looks up" the rule for the given
-// type(s).
-//
-// All of the auto-generated code can be inlined to produce zero impact on
-// run-time performance and code size (though some compilers may require
-// gentle encouragement in order for them to do so).
-
-#ifndef TALK_SESSION_PHONE_TYPEWRAPPING_H_
-#define TALK_SESSION_PHONE_TYPEWRAPPING_H_
-
-#include "webrtc/base/common.h"
-
-#ifdef OSX
-// XCode's GCC doesn't respect typedef-equivalence when casting function pointer
-// types, so we can't enforce that the wrapped function signatures strictly
-// match the expected types. Instead we have to forego the nice user-friendly
-// static_cast check (because it will spuriously fail) and make the Call()
-// function into a member template below.
-#define CAST_FUNCTION_(function, ...) \
-  function
-#else
-#define CAST_FUNCTION_(function, ...) \
-  static_cast<__VA_ARGS__>(function)
-#endif
-
-// Internal helper macros.
-#define SMART_WRAPPER_(wrapper, toType, fromType, from) \
-  (wrapper<toType, fromType>::Wrap(from))
-
-#define SMART_UNWRAPPER_(unwrapper, fromType, from) \
-  (unwrapper<fromType>::Unwrap(from))
-
-#define SMART_UNWRAPPER_TYPE_(unwrapper, fromType) \
-  typename unwrapper<fromType>::ToType
-
-$var n = 27
-$range i 0..n
-
-$for i [[
-$range j 1..i
-
-// The code that follows wraps calls to $i-argument functions, unwrapping the
-// arguments and wrapping the return value as needed.
-
-// The usual case.
-template<
-    template <typename ToType, typename FromType> class Wrapper,
-    template <typename FromType> class Unwrapper,
-    typename ReturnType$for j [[,
-    typename ArgType$j]]>
-class SmartFunctionWrapper$i {
- public:
-  typedef SMART_UNWRAPPER_TYPE_(Unwrapper, ReturnType) OriginalReturnType;
-
-$for j [[
-  typedef SMART_UNWRAPPER_TYPE_(Unwrapper, ArgType$j) OriginalArgType$j;
-
-]]
-  typedef OriginalReturnType (*OriginalFunctionType)($for j , [[
-
-      OriginalArgType$j]]);
-
-#ifdef OSX
-  template <typename F>
-  static FORCE_INLINE ReturnType Call(F function
-#else
-  static FORCE_INLINE ReturnType Call(OriginalFunctionType function
-#endif
-                                      $for j [[,
-                                      ArgType$j v$j]]) {
-    return SMART_WRAPPER_(Wrapper, ReturnType, OriginalReturnType,
-        (*function)($for j , [[
-
-            SMART_UNWRAPPER_(Unwrapper, ArgType$j, v$j)]]));
-  }
-};
-
-// Special case for functions that return void. (SMART_WRAPPER_ involves
-// passing the unwrapped value in a function call, which is not a legal thing to
-// do with void, so we need a special case here that doesn't call
-// SMART_WRAPPER_()).
-template<
-    template <typename ToType, typename FromType> class Wrapper,
-    template <typename FromType> class Unwrapper$for j [[,
-    typename ArgType$j]]>
-class SmartFunctionWrapper$i<
-    Wrapper,
-    Unwrapper,
-    void$for j [[,
-    ArgType$j]]> {
- public:
-  typedef void OriginalReturnType;
-
-$for j [[
-  typedef SMART_UNWRAPPER_TYPE_(Unwrapper, ArgType$j) OriginalArgType$j;
-
-]]
-  typedef OriginalReturnType (*OriginalFunctionType)($for j , [[
-
-      OriginalArgType$j]]);
-
-#ifdef OSX
-  template <typename F>
-  static FORCE_INLINE void Call(F function
-#else
-  static FORCE_INLINE void Call(OriginalFunctionType function
-#endif
-                                $for j [[,
-                                ArgType$j v$j]]) {
-    (*function)($for j , [[
-
-        SMART_UNWRAPPER_(Unwrapper, ArgType$j, v$j)]]);
-  }
-};
-
-
-]]
-// Programmer interface follows. Only macros below here should be used outside
-// this file.
-
-#define DECLARE_WRAPPING_RULESET(ruleSet) \
-  namespace ruleSet { \
-\
-  /* SmartWrapper is for wrapping values. */ \
-  template<typename ToType, typename FromType> \
-  class SmartWrapper; \
-\
-  /* Special case where the types are the same. */ \
-  template<typename T1> \
-  class SmartWrapper<T1, T1> { \
-   public: \
-    static FORCE_INLINE T1 Wrap(T1 from) { \
-      return from; \
-    } \
-  }; \
-\
-  /* Class for unwrapping (i.e., going to the original value). This is done
-     function-style rather than predicate-style. The default rule is to leave
-     the type unchanged. */ \
-  template<typename FromType> \
-  class SmartUnwrapper { \
-   public: \
-    typedef FromType ToType; \
-    static FORCE_INLINE ToType Unwrap(FromType from) { \
-      return from; \
-    } \
-  }; \
-\
-  }
-
-// Declares a wrapping rule.
-#define DECLARE_WRAPPER(ruleSet, wrappedType, unwrappedType, var, wrapCode, unwrapCode) \
-  namespace ruleSet { \
-\
-  template<> \
-  class SmartWrapper<wrappedType, unwrappedType> { \
-   public: \
-    static FORCE_INLINE wrappedType Wrap(unwrappedType var) { \
-      return wrapCode; \
-    } \
-  }; \
-\
-  template<> \
-  class SmartUnwrapper<wrappedType> { \
-   public: \
-    typedef unwrappedType ToType; \
-    static FORCE_INLINE unwrappedType Unwrap(wrappedType var) { \
-      return unwrapCode; \
-    } \
-  }; \
-\
-  }
-
-// Helper macro for declaring a wrapper that wraps/unwraps with reinterpret_cast<>.
-#define DECLARE_WRAPPER_BY_REINTERPRET_CAST(ruleSet, wrappedType, unwrappedType) \
-  DECLARE_WRAPPER(ruleSet, wrappedType, unwrappedType, FROM, reinterpret_cast<wrappedType>(FROM), reinterpret_cast<unwrappedType>(FROM))
-
-// Helper macro for declaring a wrapper that wraps/unwraps implicitly.
-#define DECLARE_WRAPPER_BY_IMPLICIT_CAST(ruleSet, wrappedType, unwrappedType) \
-  DECLARE_WRAPPER(ruleSet, wrappedType, unwrappedType, FROM, FROM, FROM)
-
-// Helper macro for declaring that the pointer types for one type wrap the pointer types for another type.
-#define DECLARE_POINTER_WRAPPER(ruleSet, wrappedType, unwrappedType) \
-  DECLARE_WRAPPER_BY_REINTERPRET_CAST(ruleSet, wrappedType*, unwrappedType*) \
-  DECLARE_WRAPPER_BY_REINTERPRET_CAST(ruleSet, const wrappedType*, const unwrappedType*) \
-  DECLARE_WRAPPER_BY_REINTERPRET_CAST(ruleSet, wrappedType* const, unwrappedType* const) \
-  DECLARE_WRAPPER_BY_REINTERPRET_CAST(ruleSet, const wrappedType* const, const unwrappedType* const) \
-
-// Macro to wrap a single value.
-#define WRAP(ruleSet, toType, fromType, from) \
-  SMART_WRAPPER_(ruleSet::SmartWrapper, toType, fromType, from)
-
-// Macro to unwrap a single value.
-#define UNWRAP(ruleSet, fromType, from) \
-  SMART_UNWRAPPER_(ruleSet::SmartUnwrapper, fromType, from)
-
-// Macro to get the unwrapped form of a type.
-#define UNWRAP_TYPE(ruleSet, fromType) \
-  SMART_UNWRAPPER_TYPE_(ruleSet::SmartUnwrapper, from)
-
-// Macros to wrap function calls.
-
-$for i [[
-$range j 1..i
-#define WRAP_CALL$i(ruleSet, toType, function$for j [[, argType$j, arg$j]]) \
-  (SmartFunctionWrapper$i< \
-      ruleSet::SmartWrapper, \
-      ruleSet::SmartUnwrapper, \
-      toType$for j [[, \
-      argType$j]]>::Call( \
-          CAST_FUNCTION_( \
-              &function, \
-              SmartFunctionWrapper$i< \
-                  ruleSet::SmartWrapper, \
-                  ruleSet::SmartUnwrapper, \
-                  toType$for j [[, \
-                  argType$j]]>::OriginalFunctionType)$for j [[, \
-          arg$j]]))
-
-]]
-
-#endif  // TALK_SESSION_PHONE_TYPEWRAPPINGHELPERS_H_