15821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Copyright (c) 2006-2009 The Chromium Authors. All rights reserved. 25821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Use of this source code is governed by a BSD-style license that can be 35821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// found in the LICENSE file. 45821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 55821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Template metaprogramming utility functions. 65821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 75821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// This code is compiled directly on many platforms, including client 85821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// platforms like Windows, Mac, and embedded systems. Before making 95821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// any changes here, make sure that you're not breaking any platforms. 105821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 115821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// The names choosen here reflect those used in tr1 and the boost::mpl 125821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// library, there are similar operations used in the Loki library as 135821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// well. I prefer the boost names for 2 reasons: 145821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 1. I think that portions of the Boost libraries are more likely to 155821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// be included in the c++ standard. 165821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 2. It is not impossible that some of the boost libraries will be 175821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// included in our own build in the future. 185821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Both of these outcomes means that we may be able to directly replace 195821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// some of these with boost equivalents. 205821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 215821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#ifndef BASE_TEMPLATE_UTIL_H_ 225821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#define BASE_TEMPLATE_UTIL_H_ 235821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 245821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)namespace base { 255821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 265821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Types small_ and big_ are guaranteed such that sizeof(small_) < 275821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// sizeof(big_) 285821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)typedef char small_; 295821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 305821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)struct big_ { 315821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) char dummy[2]; 325821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 335821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 345821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// integral_constant, defined in tr1, is a wrapper for an integer 355821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// value. We don't really need this generality; we could get away 365821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// with hardcoding the integer type to bool. We use the fully 375821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// general integer_constant for compatibility with tr1. 385821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 395821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template<class T, T v> 405821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)struct integral_constant { 415821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) static const T value = v; 425821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) typedef T value_type; 435821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) typedef integral_constant<T, v> type; 445821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 455821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 465821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <class T, T v> const T integral_constant<T, v>::value; 475821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 485821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 495821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Abbreviations: true_type and false_type are structs that represent boolean 505821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// true and false values. Also define the boost::mpl versions of those names, 515821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// true_ and false_. 525821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)typedef integral_constant<bool, true> true_type; 535821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)typedef integral_constant<bool, false> false_type; 545821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)typedef true_type true_; 555821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)typedef false_type false_; 565821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 575821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// if_ is a templatized conditional statement. 585821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// if_<cond, A, B> is a compile time evaluation of cond. 595821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// if_<>::type contains A if cond is true, B otherwise. 605821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template<bool cond, typename A, typename B> 615821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)struct if_{ 625821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) typedef A type; 635821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 645821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 655821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template<typename A, typename B> 665821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)struct if_<false, A, B> { 675821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) typedef B type; 685821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 695821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 705821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 715821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// type_equals_ is a template type comparator, similar to Loki IsSameType. 725821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// type_equals_<A, B>::value is true iff "A" is the same type as "B". 735821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template<typename A, typename B> 745821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)struct type_equals_ : public false_ { 755821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 765821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 775821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template<typename A> 785821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)struct type_equals_<A, A> : public true_ { 795821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 805821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 815821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// and_ is a template && operator. 825821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// and_<A, B>::value evaluates "A::value && B::value". 835821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template<typename A, typename B> 845821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)struct and_ : public integral_constant<bool, (A::value && B::value)> { 855821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 865821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 875821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// or_ is a template || operator. 885821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// or_<A, B>::value evaluates "A::value || B::value". 895821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template<typename A, typename B> 905821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)struct or_ : public integral_constant<bool, (A::value || B::value)> { 915821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 925821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 935821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 945821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)} // Close namespace base 955821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 965821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#endif // BASE_TEMPLATE_UTIL_H_ 97