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FormatVariadic.h
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1 //===- FormatVariadic.h - Efficient type-safe string formatting --*- C++-*-===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements the formatv() function which can be used with other LLVM
11 // subsystems to provide printf-like formatting, but with improved safety and
12 // flexibility. The result of `formatv` is an object which can be streamed to
13 // a raw_ostream or converted to a std::string or llvm::SmallString.
14 //
15 // // Convert to std::string.
16 // std::string S = formatv("{0} {1}", 1234.412, "test").str();
17 //
18 // // Convert to llvm::SmallString
19 // SmallString<8> S = formatv("{0} {1}", 1234.412, "test").sstr<8>();
20 //
21 // // Stream to an existing raw_ostream.
22 // OS << formatv("{0} {1}", 1234.412, "test");
23 //
24 //===----------------------------------------------------------------------===//
25 
26 #ifndef LLVM_SUPPORT_FORMATVARIADIC_H
27 #define LLVM_SUPPORT_FORMATVARIADIC_H
28 
29 #include "llvm/ADT/Optional.h"
30 #include "llvm/ADT/STLExtras.h"
31 #include "llvm/ADT/SmallString.h"
32 #include "llvm/ADT/StringRef.h"
37 #include <cstddef>
38 #include <string>
39 #include <tuple>
40 #include <utility>
41 #include <vector>
42 
43 namespace llvm {
44 
46 
48  ReplacementItem() = default;
49  explicit ReplacementItem(StringRef Literal)
50  : Type(ReplacementType::Literal), Spec(Literal) {}
51  ReplacementItem(StringRef Spec, size_t Index, size_t Align, AlignStyle Where,
52  char Pad, StringRef Options)
53  : Type(ReplacementType::Format), Spec(Spec), Index(Index), Align(Align),
54  Where(Where), Pad(Pad), Options(Options) {}
55 
58  size_t Index = 0;
59  size_t Align = 0;
61  char Pad;
63 };
64 
66 protected:
67  // The parameters are stored in a std::tuple, which does not provide runtime
68  // indexing capabilities. In order to enable runtime indexing, we use this
69  // structure to put the parameters into a std::vector. Since the parameters
70  // are not all the same type, we use some type-erasure by wrapping the
71  // parameters in a template class that derives from a non-template superclass.
72  // Essentially, we are converting a std::tuple<Derived<Ts...>> to a
73  // std::vector<Base*>.
74  struct create_adapters {
75  template <typename... Ts>
76  std::vector<detail::format_adapter *> operator()(Ts &... Items) {
77  return std::vector<detail::format_adapter *>{&Items...};
78  }
79  };
80 
82  std::vector<detail::format_adapter *> Adapters;
83  std::vector<ReplacementItem> Replacements;
84 
85  static bool consumeFieldLayout(StringRef &Spec, AlignStyle &Where,
86  size_t &Align, char &Pad);
87 
88  static std::pair<ReplacementItem, StringRef>
89  splitLiteralAndReplacement(StringRef Fmt);
90 
91 public:
92  formatv_object_base(StringRef Fmt, std::size_t ParamCount)
93  : Fmt(Fmt), Replacements(parseFormatString(Fmt)) {
94  Adapters.reserve(ParamCount);
95  }
96 
97  formatv_object_base(formatv_object_base const &rhs) = delete;
98 
100  : Fmt(std::move(rhs.Fmt)),
101  Adapters(), // Adapters are initialized by formatv_object
102  Replacements(std::move(rhs.Replacements)) {
103  Adapters.reserve(rhs.Adapters.size());
104  };
105 
106  void format(raw_ostream &S) const {
107  for (auto &R : Replacements) {
108  if (R.Type == ReplacementType::Empty)
109  continue;
110  if (R.Type == ReplacementType::Literal) {
111  S << R.Spec;
112  continue;
113  }
114  if (R.Index >= Adapters.size()) {
115  S << R.Spec;
116  continue;
117  }
118 
119  auto W = Adapters[R.Index];
120 
121  FmtAlign Align(*W, R.Where, R.Align);
122  Align.format(S, R.Options);
123  }
124  }
125  static std::vector<ReplacementItem> parseFormatString(StringRef Fmt);
126 
127  static Optional<ReplacementItem> parseReplacementItem(StringRef Spec);
128 
129  std::string str() const {
130  std::string Result;
131  raw_string_ostream Stream(Result);
132  Stream << *this;
133  Stream.flush();
134  return Result;
135  }
136 
137  template <unsigned N> SmallString<N> sstr() const {
138  SmallString<N> Result;
139  raw_svector_ostream Stream(Result);
140  Stream << *this;
141  return Result;
142  }
143 
144  template <unsigned N> operator SmallString<N>() const { return sstr<N>(); }
145 
146  operator std::string() const { return str(); }
147 };
148 
149 template <typename Tuple> class formatv_object : public formatv_object_base {
150  // Storage for the parameter adapters. Since the base class erases the type
151  // of the parameters, we have to own the storage for the parameters here, and
152  // have the base class store type-erased pointers into this tuple.
153  Tuple Parameters;
154 
155 public:
156  formatv_object(StringRef Fmt, Tuple &&Params)
157  : formatv_object_base(Fmt, std::tuple_size<Tuple>::value),
158  Parameters(std::move(Params)) {
159  Adapters = apply_tuple(create_adapters(), Parameters);
160  }
161 
162  formatv_object(formatv_object const &rhs) = delete;
163 
165  : formatv_object_base(std::move(rhs)),
166  Parameters(std::move(rhs.Parameters)) {
167  Adapters = apply_tuple(create_adapters(), Parameters);
168  }
169 };
170 
171 // \brief Format text given a format string and replacement parameters.
172 //
173 // ===General Description===
174 //
175 // Formats textual output. `Fmt` is a string consisting of one or more
176 // replacement sequences with the following grammar:
177 //
178 // rep_field ::= "{" [index] ["," layout] [":" format] "}"
179 // index ::= <non-negative integer>
180 // layout ::= [[[char]loc]width]
181 // format ::= <any string not containing "{" or "}">
182 // char ::= <any character except "{" or "}">
183 // loc ::= "-" | "=" | "+"
184 // width ::= <positive integer>
185 //
186 // index - A non-negative integer specifying the index of the item in the
187 // parameter pack to print. Any other value is invalid.
188 // layout - A string controlling how the field is laid out within the available
189 // space.
190 // format - A type-dependent string used to provide additional options to
191 // the formatting operation. Refer to the documentation of the
192 // various individual format providers for per-type options.
193 // char - The padding character. Defaults to ' ' (space). Only valid if
194 // `loc` is also specified.
195 // loc - Where to print the formatted text within the field. Only valid if
196 // `width` is also specified.
197 // '-' : The field is left aligned within the available space.
198 // '=' : The field is centered within the available space.
199 // '+' : The field is right aligned within the available space (this
200 // is the default).
201 // width - The width of the field within which to print the formatted text.
202 // If this is less than the required length then the `char` and `loc`
203 // fields are ignored, and the field is printed with no leading or
204 // trailing padding. If this is greater than the required length,
205 // then the text is output according to the value of `loc`, and padded
206 // as appropriate on the left and/or right by `char`.
207 //
208 // ===Special Characters===
209 //
210 // The characters '{' and '}' are reserved and cannot appear anywhere within a
211 // replacement sequence. Outside of a replacement sequence, in order to print
212 // a literal '{' or '}' it must be doubled -- "{{" to print a literal '{' and
213 // "}}" to print a literal '}'.
214 //
215 // ===Parameter Indexing===
216 // `index` specifies the index of the parameter in the parameter pack to format
217 // into the output. Note that it is possible to refer to the same parameter
218 // index multiple times in a given format string. This makes it possible to
219 // output the same value multiple times without passing it multiple times to the
220 // function. For example:
221 //
222 // formatv("{0} {1} {0}", "a", "bb")
223 //
224 // would yield the string "abba". This can be convenient when it is expensive
225 // to compute the value of the parameter, and you would otherwise have had to
226 // save it to a temporary.
227 //
228 // ===Formatter Search===
229 //
230 // For a given parameter of type T, the following steps are executed in order
231 // until a match is found:
232 //
233 // 1. If the parameter is of class type, and inherits from format_adapter,
234 // Then format() is invoked on it to produce the formatted output. The
235 // implementation should write the formatted text into `Stream`.
236 // 2. If there is a suitable template specialization of format_provider<>
237 // for type T containing a method whose signature is:
238 // void format(const T &Obj, raw_ostream &Stream, StringRef Options)
239 // Then this method is invoked as described in Step 1.
240 //
241 // If a match cannot be found through either of the above methods, a compiler
242 // error is generated.
243 //
244 // ===Invalid Format String Handling===
245 //
246 // In the case of a format string which does not match the grammar described
247 // above, the output is undefined. With asserts enabled, LLVM will trigger an
248 // assertion. Otherwise, it will try to do something reasonable, but in general
249 // the details of what that is are undefined.
250 //
251 template <typename... Ts>
252 inline auto formatv(const char *Fmt, Ts &&... Vals) -> formatv_object<decltype(
253  std::make_tuple(detail::build_format_adapter(std::forward<Ts>(Vals))...))> {
254  using ParamTuple = decltype(
255  std::make_tuple(detail::build_format_adapter(std::forward<Ts>(Vals))...));
257  Fmt,
258  std::make_tuple(detail::build_format_adapter(std::forward<Ts>(Vals))...));
259 }
260 
261 // Allow a formatv_object to be formatted (no options supported).
262 template <typename T> struct format_provider<formatv_object<T>> {
263  static void format(const formatv_object<T> &V, raw_ostream &OS, StringRef) {
264  OS << V;
265  }
266 };
267 
268 } // end namespace llvm
269 
270 #endif // LLVM_SUPPORT_FORMATVARIADIC_H
constexpr char Align[]
Key for Kernel::Arg::Metadata::mAlign.
ReplacementItem(StringRef Literal)
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
formatv_object_base(StringRef Fmt, std::size_t ParamCount)
A raw_ostream that writes to an SmallVector or SmallString.
Definition: raw_ostream.h:489
auto formatv(const char *Fmt, Ts &&... Vals) -> formatv_object< decltype(std::make_tuple(detail::build_format_adapter(std::forward< Ts >(Vals))...))>
void format(raw_ostream &S, StringRef Options)
Definition: FormatCommon.h:30
Definition: BitVector.h:920
ReplacementType
SmallString< N > sstr() const
std::vector< detail::format_adapter * > Adapters
auto apply_tuple(F &&f, Tuple &&t) -> decltype(detail::apply_tuple_impl(std::forward< F >(f), std::forward< Tuple >(t), build_index_impl< std::tuple_size< typename std::decay< Tuple >::type >::value >
Given an input tuple (a1, a2, ..., an), pass the arguments of the tuple variadically to f as if by ca...
Definition: STLExtras.h:1130
SmallString - A SmallString is just a SmallVector with methods and accessors that make it work better...
Definition: SmallString.h:26
formatv_object(formatv_object &&rhs)
The instances of the Type class are immutable: once they are created, they are never changed...
Definition: Type.h:46
AlignStyle
Definition: FormatCommon.h:18
void format(raw_ostream &S) const
std::vector< ReplacementItem > Replacements
ReplacementItem(StringRef Spec, size_t Index, size_t Align, AlignStyle Where, char Pad, StringRef Options)
std::vector< detail::format_adapter * > operator()(Ts &... Items)
formatv_object_base(formatv_object_base &&rhs)
formatv_object(StringRef Fmt, Tuple &&Params)
std::enable_if< uses_format_member< T >::value, T >::type build_format_adapter(T &&Item)
A raw_ostream that writes to an std::string.
Definition: raw_ostream.h:462
std::string str() const
static void format(const formatv_object< T > &V, raw_ostream &OS, StringRef)
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:44
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:49