1 /*
2  * Copyright 2013 Google Inc.
3  *
4  * Use of this source code is governed by a BSD-style license that can be
5  * found in the LICENSE file.
6  *
7  *
8  * This header provides some of the helpers (like std::enable_if_t) which will
9  * become available with C++14 in the type_traits header (in the skstd
10  * namespace). This header also provides several Skia specific additions such
11  * as SK_WHEN and the sknonstd namespace.
12  */
13 
14 #ifndef SkTLogic_DEFINED
15 #define SkTLogic_DEFINED
16 
17 #include "SkTypes.h"
18 
19 #include <stddef.h>
20 #include <stdint.h>
21 #include <type_traits>
22 #include <utility>
23 
24 namespace skstd {
25 
26 template <bool B> using bool_constant = std::integral_constant<bool, B>;
27 
28 template <bool B, typename T, typename F> using conditional_t = typename std::conditional<B, T, F>::type;
29 template <bool B, typename T = void> using enable_if_t = typename std::enable_if<B, T>::type;
30 
31 template <typename T> using remove_const_t = typename std::remove_const<T>::type;
32 template <typename T> using remove_volatile_t = typename std::remove_volatile<T>::type;
33 template <typename T> using remove_cv_t = typename std::remove_cv<T>::type;
34 template <typename T> using remove_pointer_t = typename std::remove_pointer<T>::type;
35 template <typename T> using remove_reference_t = typename std::remove_reference<T>::type;
36 template <typename T> using remove_extent_t = typename std::remove_extent<T>::type;
37 
38 // template<typename R, typename... Args> struct is_function<
39 //     R [calling-convention] (Args...[, ...]) [const] [volatile] [&|&&]> : std::true_type {};
40 // The cv and ref-qualified versions are strange types we're currently avoiding, so not supported.
41 // These aren't supported in msvc either until vs2015u2.
42 // On all platforms, variadic functions only exist in the c calling convention.
43 // mcvc 2013 introduced __vectorcall, but it wan't until 2015 that it was added to is_function.
44 template <typename> struct is_function : std::false_type {};
45 #if !defined(SK_BUILD_FOR_WIN)
46 template <typename R, typename... Args> struct is_function<R(Args...)> : std::true_type {};
47 #else
48 template <typename R, typename... Args> struct is_function<R __cdecl (Args...)> : std::true_type {};
49 #if defined(_M_IX86)
50 template <typename R, typename... Args> struct is_function<R __stdcall (Args...)> : std::true_type {};
51 template <typename R, typename... Args> struct is_function<R __fastcall (Args...)> : std::true_type {};
52 #endif
53 #if defined(_MSC_VER) && SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2
54 template <typename R, typename... Args> struct is_function<R __vectorcall (Args...)> : std::true_type {};
55 #endif
56 #endif
57 template <typename R, typename... Args> struct is_function<R(Args..., ...)> : std::true_type {};
58 
59 template <typename T> using add_const_t = typename std::add_const<T>::type;
60 template <typename T> using add_volatile_t = typename std::add_volatile<T>::type;
61 template <typename T> using add_cv_t = typename std::add_cv<T>::type;
62 template <typename T> using add_pointer_t = typename std::add_pointer<T>::type;
63 template <typename T> using add_lvalue_reference_t = typename std::add_lvalue_reference<T>::type;
64 
65 template <typename S, typename D,
66           bool=std::is_void<S>::value || is_function<D>::value || std::is_array<D>::value>
67 struct is_convertible_detector {
68     static const/*expr*/ bool value = std::is_void<D>::value;
69 };
70 template <typename S, typename D> struct is_convertible_detector<S, D, false> {
71     using yes_type = uint8_t;
72     using no_type = uint16_t;
73 
74     template <typename To> static void param_convertable_to(To);
75 
76     template <typename From, typename To>
77     static decltype(param_convertable_to<To>(std::declval<From>()), yes_type()) convertible(int);
78 
79     template <typename, typename> static no_type convertible(...);
80 
81     static const/*expr*/ bool value = sizeof(convertible<S, D>(0)) == sizeof(yes_type);
82 };
83 // std::is_convertable is known to be broken (not work with incomplete types) in Android clang NDK.
84 // This is currently what prevents us from using std::unique_ptr.
85 template<typename S, typename D> struct is_convertible
86     : bool_constant<is_convertible_detector<S, D>::value> {};
87 
88 }  // namespace skstd
89 
90 // The sknonstd namespace contains things we would like to be proposed and feel std-ish.
91 namespace sknonstd {
92 
93 // The name 'copy' here is fraught with peril. In this case it means 'append', not 'overwrite'.
94 // Alternate proposed names are 'propagate', 'augment', or 'append' (and 'add', but already taken).
95 // std::experimental::propagate_const already exists for other purposes in TSv2.
96 // These also follow the <dest, source> pattern used by boost.
97 template <typename D, typename S> struct copy_const {
98     using type = skstd::conditional_t<std::is_const<S>::value, skstd::add_const_t<D>, D>;
99 };
100 template <typename D, typename S> using copy_const_t = typename copy_const<D, S>::type;
101 
102 template <typename D, typename S> struct copy_volatile {
103     using type = skstd::conditional_t<std::is_volatile<S>::value, skstd::add_volatile_t<D>, D>;
104 };
105 template <typename D, typename S> using copy_volatile_t = typename copy_volatile<D, S>::type;
106 
107 template <typename D, typename S> struct copy_cv {
108     using type = copy_volatile_t<copy_const_t<D, S>, S>;
109 };
110 template <typename D, typename S> using copy_cv_t = typename copy_cv<D, S>::type;
111 
112 // The name 'same' here means 'overwrite'.
113 // Alternate proposed names are 'replace', 'transfer', or 'qualify_from'.
114 // same_xxx<D, S> can be written as copy_xxx<remove_xxx_t<D>, S>
115 template <typename D, typename S> using same_const = copy_const<skstd::remove_const_t<D>, S>;
116 template <typename D, typename S> using same_const_t = typename same_const<D, S>::type;
117 template <typename D, typename S> using same_volatile =copy_volatile<skstd::remove_volatile_t<D>,S>;
118 template <typename D, typename S> using same_volatile_t = typename same_volatile<D, S>::type;
119 template <typename D, typename S> using same_cv = copy_cv<skstd::remove_cv_t<D>, S>;
120 template <typename D, typename S> using same_cv_t = typename same_cv<D, S>::type;
121 
122 }  // namespace sknonstd
123 
124 // Just a pithier wrapper for enable_if_t.
125 #define SK_WHEN(condition, T) skstd::enable_if_t<!!(condition), T>
126 
127 #endif
128