example-typelist.cpp source code [clang_source_code/test/SemaTemplate/example-typelist.cpp]

1	// RUN: %clang_cc1 -fsyntax-only -verify %s
2	// expected-no-diagnostics
3
4	// A simple cons-style typelist
5	struct nil { };
6
7	template<typename Head, typename Tail = nil>
8	struct cons {
9	typedef Head head;
10	typedef Tail tail;
11	};
12
13	// is_same trait, for testing
14	template<typename T, typename U>
15	struct is_same {
16	static const bool value = false;
17	};
18
19	template<typename T>
20	struct is_same<T, T> {
21	static const bool value = true;
22	};
23
24	// metaprogram that computes the length of a list
25	template<typename T> struct length;
26
27	template<typename Head, typename Tail>
28	struct length<cons<Head, Tail> > {
29	static const unsigned value = length<Tail>::value + 1;
30	};
31
32	template<>
33	struct length<nil> {
34	static const unsigned value = 0;
35	};
36
37	typedef cons<unsigned char,
38	cons<unsigned short,
39	cons<unsigned int,
40	cons<unsigned long> > > > unsigned_inttypes;
41	int length0[length<unsigned_inttypes>::value == 4? 1 : -1];
42
43	// metaprogram that reverses a list
44
45	// FIXME: I would prefer that this be a partial specialization, but
46	// that requires partial ordering of class template partial
47	// specializations.
48	template<typename T>
49	class reverse {
50	typedef typename reverse<typename T::tail>::type reversed_tail;
51
52	typedef typename reverse<typename reversed_tail::tail>::type most_of_tail;
53
54	public:
55	typedef cons<typename reversed_tail::head,
56	typename reverse<cons<typename T::head, most_of_tail> >::type> type;
57	};
58
59	template<typename Head>
60	class reverse<cons<Head> > {
61	public:
62	typedef cons<Head> type;
63	};
64
65	template<>
66	class reverse<nil> {
67	public:
68	typedef nil type;
69	};
70
71	int reverse0[is_same<reverse<unsigned_inttypes>::type,
72	cons<unsigned long,
73	cons<unsigned int,
74	cons<unsigned short,
75	cons<unsigned char> > > > >::value? 1 : -1];
76
77	// metaprogram that finds a type within a list
78
79	// FIXME: I would prefer that this be a partial specialization, but
80	// that requires partial ordering of class template partial
81	// specializations.
82	template<typename List, typename T>
83	struct find : find<typename List::tail, T> { };
84
85	template<typename Tail, typename T>
86	struct find<cons<T, Tail>, T> {
87	typedef cons<T, Tail> type;
88	};
89
90	template<typename T>
91	struct find<nil, T> {
92	typedef nil type;
93	};
94
95	int find0[is_same<find<unsigned_inttypes, unsigned int>::type,
96	cons<unsigned int, cons<unsigned long> > >::value?
97	1 : -1];
98	int find1[is_same<find<unsigned_inttypes, int>::type, nil>::value? 1 : -1];
99
100

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