1 //===- FormatVariadic.h - Efficient type-safe string formatting --*- C++-*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
15 // // Convert to std::string.
16 // std::string S = formatv("{0} {1}", 1234.412, "test").str();
18 // // Convert to llvm::SmallString
19 // SmallString<8> S = formatv("{0} {1}", 1234.412, "test").sstr<8>();
21 // // Stream to an existing raw_ostream.
22 // OS << formatv("{0} {1}", 1234.412, "test");
24 //===----------------------------------------------------------------------===//
26 #ifndef LLVM_SUPPORT_FORMATVARIADIC_H
27 #define LLVM_SUPPORT_FORMATVARIADIC_H
29 #include "llvm/ADT/Optional.h"
30 #include "llvm/ADT/SmallString.h"
31 #include "llvm/ADT/STLExtras.h"
32 #include "llvm/ADT/StringRef.h"
33 #include "llvm/Support/FormatCommon.h"
34 #include "llvm/Support/FormatProviders.h"
35 #include "llvm/Support/FormatVariadicDetails.h"
36 #include "llvm/Support/raw_ostream.h"
45 enum class ReplacementType { Empty, Format, Literal };
47 struct ReplacementItem {
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) {}
56 ReplacementType Type = ReplacementType::Empty;
60 AlignStyle Where = AlignStyle::Right;
65 class formatv_object_base {
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...};
82 std::vector<detail::format_adapter *> Adapters;
83 std::vector<ReplacementItem> Replacements;
85 static bool consumeFieldLayout(StringRef &Spec, AlignStyle &Where,
86 size_t &Align, char &Pad);
88 static std::pair<ReplacementItem, StringRef>
89 splitLiteralAndReplacement(StringRef Fmt);
92 formatv_object_base(StringRef Fmt, std::size_t ParamCount)
93 : Fmt(Fmt), Replacements(parseFormatString(Fmt)) {
94 Adapters.reserve(ParamCount);
97 void format(raw_ostream &S) const {
98 for (auto &R : Replacements) {
99 if (R.Type == ReplacementType::Empty)
101 if (R.Type == ReplacementType::Literal) {
105 if (R.Index >= Adapters.size()) {
110 auto W = Adapters[R.Index];
112 FmtAlign Align(*W, R.Where, R.Align);
113 Align.format(S, R.Options);
116 static std::vector<ReplacementItem> parseFormatString(StringRef Fmt);
118 static Optional<ReplacementItem> parseReplacementItem(StringRef Spec);
120 std::string str() const {
122 raw_string_ostream Stream(Result);
128 template <unsigned N> SmallString<N> sstr() const {
129 SmallString<N> Result;
130 raw_svector_ostream Stream(Result);
135 template <unsigned N> operator SmallString<N>() const { return sstr<N>(); }
137 operator std::string() const { return str(); }
140 template <typename Tuple> class formatv_object : public formatv_object_base {
141 // Storage for the parameter adapters. Since the base class erases the type
142 // of the parameters, we have to own the storage for the parameters here, and
143 // have the base class store type-erased pointers into this tuple.
147 formatv_object(StringRef Fmt, Tuple &&Params)
148 : formatv_object_base(Fmt, std::tuple_size<Tuple>::value),
149 Parameters(std::move(Params)) {
150 Adapters = apply_tuple(create_adapters(), Parameters);
154 // \brief Format text given a format string and replacement parameters.
156 // ===General Description===
158 // Formats textual output. `Fmt` is a string consisting of one or more
159 // replacement sequences with the following grammar:
161 // rep_field ::= "{" [index] ["," layout] [":" format] "}"
162 // index ::= <non-negative integer>
163 // layout ::= [[[char]loc]width]
164 // format ::= <any string not containing "{" or "}">
165 // char ::= <any character except "{" or "}">
166 // loc ::= "-" | "=" | "+"
167 // width ::= <positive integer>
169 // index - A non-negative integer specifying the index of the item in the
170 // parameter pack to print. Any other value is invalid.
171 // layout - A string controlling how the field is laid out within the available
173 // format - A type-dependent string used to provide additional options to
174 // the formatting operation. Refer to the documentation of the
175 // various individual format providers for per-type options.
176 // char - The padding character. Defaults to ' ' (space). Only valid if
177 // `loc` is also specified.
178 // loc - Where to print the formatted text within the field. Only valid if
179 // `width` is also specified.
180 // '-' : The field is left aligned within the available space.
181 // '=' : The field is centered within the available space.
182 // '+' : The field is right aligned within the available space (this
184 // width - The width of the field within which to print the formatted text.
185 // If this is less than the required length then the `char` and `loc`
186 // fields are ignored, and the field is printed with no leading or
187 // trailing padding. If this is greater than the required length,
188 // then the text is output according to the value of `loc`, and padded
189 // as appropriate on the left and/or right by `char`.
191 // ===Special Characters===
193 // The characters '{' and '}' are reserved and cannot appear anywhere within a
194 // replacement sequence. Outside of a replacement sequence, in order to print
195 // a literal '{' or '}' it must be doubled -- "{{" to print a literal '{' and
196 // "}}" to print a literal '}'.
198 // ===Parameter Indexing===
199 // `index` specifies the index of the parameter in the parameter pack to format
200 // into the output. Note that it is possible to refer to the same parameter
201 // index multiple times in a given format string. This makes it possible to
202 // output the same value multiple times without passing it multiple times to the
203 // function. For example:
205 // formatv("{0} {1} {0}", "a", "bb")
207 // would yield the string "abba". This can be convenient when it is expensive
208 // to compute the value of the parameter, and you would otherwise have had to
209 // save it to a temporary.
211 // ===Formatter Search===
213 // For a given parameter of type T, the following steps are executed in order
214 // until a match is found:
216 // 1. If the parameter is of class type, and contains a method
217 // void format(raw_ostream &Stream, StringRef Options)
218 // Then this method is invoked to produce the formatted output. The
219 // implementation should write the formatted text into `Stream`.
220 // 2. If there is a suitable template specialization of format_provider<>
221 // for type T containing a method whose signature is:
222 // void format(const T &Obj, raw_ostream &Stream, StringRef Options)
223 // Then this method is invoked as described in Step 1.
225 // If a match cannot be found through either of the above methods, a compiler
226 // error is generated.
228 // ===Invalid Format String Handling===
230 // In the case of a format string which does not match the grammar described
231 // above, the output is undefined. With asserts enabled, LLVM will trigger an
232 // assertion. Otherwise, it will try to do something reasonable, but in general
233 // the details of what that is are undefined.
235 template <typename... Ts>
236 inline auto formatv(const char *Fmt, Ts &&... Vals) -> formatv_object<decltype(
237 std::make_tuple(detail::build_format_adapter(std::forward<Ts>(Vals))...))> {
238 using ParamTuple = decltype(
239 std::make_tuple(detail::build_format_adapter(std::forward<Ts>(Vals))...));
240 return formatv_object<ParamTuple>(
242 std::make_tuple(detail::build_format_adapter(std::forward<Ts>(Vals))...));
245 } // end namespace llvm
247 #endif // LLVM_SUPPORT_FORMATVARIADIC_H