1//
2// Copyright 2017 The Abseil Authors.
3//
4// Licensed under the Apache License, Version 2.0 (the "License");
5// you may not use this file except in compliance with the License.
6// You may obtain a copy of the License at
7//
8// https://www.apache.org/licenses/LICENSE-2.0
9//
10// Unless required by applicable law or agreed to in writing, software
11// distributed under the License is distributed on an "AS IS" BASIS,
12// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13// See the License for the specific language governing permissions and
14// limitations under the License.
15//
16// -----------------------------------------------------------------------------
17// span.h
18// -----------------------------------------------------------------------------
19//
20// This header file defines a `Span<T>` type for holding a view of an existing
21// array of data. The `Span` object, much like the `absl::string_view` object,
22// does not own such data itself. A span provides a lightweight way to pass
23// around view of such data.
24//
25// Additionally, this header file defines `MakeSpan()` and `MakeConstSpan()`
26// factory functions, for clearly creating spans of type `Span<T>` or read-only
27// `Span<const T>` when such types may be difficult to identify due to issues
28// with implicit conversion.
29//
30// The C++ standards committee currently has a proposal for a `std::span` type,
31// (http://wg21.link/p0122), which is not yet part of the standard (though may
32// become part of C++20). As of August 2017, the differences between
33// `absl::Span` and this proposal are:
34// * `absl::Span` uses `size_t` for `size_type`
35// * `absl::Span` has no `operator()`
36// * `absl::Span` has no constructors for `std::unique_ptr` or
37// `std::shared_ptr`
38// * `absl::Span` has the factory functions `MakeSpan()` and
39// `MakeConstSpan()`
40// * `absl::Span` has `front()` and `back()` methods
41// * bounds-checked access to `absl::Span` is accomplished with `at()`
42// * `absl::Span` has compiler-provided move and copy constructors and
43// assignment. This is due to them being specified as `constexpr`, but that
44// implies const in C++11.
45// * `absl::Span` has no `element_type` or `index_type` typedefs
46// * A read-only `absl::Span<const T>` can be implicitly constructed from an
47// initializer list.
48// * `absl::Span` has no `bytes()`, `size_bytes()`, `as_bytes()`, or
49// `as_mutable_bytes()` methods
50// * `absl::Span` has no static extent template parameter, nor constructors
51// which exist only because of the static extent parameter.
52// * `absl::Span` has an explicit mutable-reference constructor
53//
54// For more information, see the class comments below.
55#ifndef ABSL_TYPES_SPAN_H_
56#define ABSL_TYPES_SPAN_H_
57
58#include <algorithm>
59#include <cassert>
60#include <cstddef>
61#include <initializer_list>
62#include <iterator>
63#include <type_traits>
64#include <utility>
65
66#include "absl/base/internal/throw_delegate.h"
67#include "absl/base/macros.h"
68#include "absl/base/optimization.h"
69#include "absl/base/port.h" // TODO(strel): remove this include
70#include "absl/meta/type_traits.h"
71#include "absl/types/internal/span.h"
72
73namespace absl {
74
75//------------------------------------------------------------------------------
76// Span
77//------------------------------------------------------------------------------
78//
79// A `Span` is an "array view" type for holding a view of a contiguous data
80// array; the `Span` object does not and cannot own such data itself. A span
81// provides an easy way to provide overloads for anything operating on
82// contiguous sequences without needing to manage pointers and array lengths
83// manually.
84
85// A span is conceptually a pointer (ptr) and a length (size) into an already
86// existing array of contiguous memory; the array it represents references the
87// elements "ptr[0] .. ptr[size-1]". Passing a properly-constructed `Span`
88// instead of raw pointers avoids many issues related to index out of bounds
89// errors.
90//
91// Spans may also be constructed from containers holding contiguous sequences.
92// Such containers must supply `data()` and `size() const` methods (e.g
93// `std::vector<T>`, `absl::InlinedVector<T, N>`). All implicit conversions to
94// `absl::Span` from such containers will create spans of type `const T`;
95// spans which can mutate their values (of type `T`) must use explicit
96// constructors.
97//
98// A `Span<T>` is somewhat analogous to an `absl::string_view`, but for an array
99// of elements of type `T`. A user of `Span` must ensure that the data being
100// pointed to outlives the `Span` itself.
101//
102// You can construct a `Span<T>` in several ways:
103//
104// * Explicitly from a reference to a container type
105// * Explicitly from a pointer and size
106// * Implicitly from a container type (but only for spans of type `const T`)
107// * Using the `MakeSpan()` or `MakeConstSpan()` factory functions.
108//
109// Examples:
110//
111// // Construct a Span explicitly from a container:
112// std::vector<int> v = {1, 2, 3, 4, 5};
113// auto span = absl::Span<const int>(v);
114//
115// // Construct a Span explicitly from a C-style array:
116// int a[5] = {1, 2, 3, 4, 5};
117// auto span = absl::Span<const int>(a);
118//
119// // Construct a Span implicitly from a container
120// void MyRoutine(absl::Span<const int> a) {
121// ...
122// }
123// std::vector v = {1,2,3,4,5};
124// MyRoutine(v) // convert to Span<const T>
125//
126// Note that `Span` objects, in addition to requiring that the memory they
127// point to remains alive, must also ensure that such memory does not get
128// reallocated. Therefore, to avoid undefined behavior, containers with
129// associated span views should not invoke operations that may reallocate memory
130// (such as resizing) or invalidate iterators into the container.
131//
132// One common use for a `Span` is when passing arguments to a routine that can
133// accept a variety of array types (e.g. a `std::vector`, `absl::InlinedVector`,
134// a C-style array, etc.). Instead of creating overloads for each case, you
135// can simply specify a `Span` as the argument to such a routine.
136//
137// Example:
138//
139// void MyRoutine(absl::Span<const int> a) {
140// ...
141// }
142//
143// std::vector v = {1,2,3,4,5};
144// MyRoutine(v);
145//
146// absl::InlinedVector<int, 4> my_inline_vector;
147// MyRoutine(my_inline_vector);
148//
149// // Explicit constructor from pointer,size
150// int* my_array = new int[10];
151// MyRoutine(absl::Span<const int>(my_array, 10));
152template <typename T>
153class Span {
154 private:
155 // Used to determine whether a Span can be constructed from a container of
156 // type C.
157 template <typename C>
158 using EnableIfConvertibleFrom =
159 typename std::enable_if<span_internal::HasData<T, C>::value &&
160 span_internal::HasSize<C>::value>::type;
161
162 // Used to SFINAE-enable a function when the slice elements are const.
163 template <typename U>
164 using EnableIfConstView =
165 typename std::enable_if<std::is_const<T>::value, U>::type;
166
167 // Used to SFINAE-enable a function when the slice elements are mutable.
168 template <typename U>
169 using EnableIfMutableView =
170 typename std::enable_if<!std::is_const<T>::value, U>::type;
171
172 public:
173 using value_type = absl::remove_cv_t<T>;
174 using pointer = T*;
175 using const_pointer = const T*;
176 using reference = T&;
177 using const_reference = const T&;
178 using iterator = pointer;
179 using const_iterator = const_pointer;
180 using reverse_iterator = std::reverse_iterator<iterator>;
181 using const_reverse_iterator = std::reverse_iterator<const_iterator>;
182 using size_type = size_t;
183 using difference_type = ptrdiff_t;
184
185 static const size_type npos = ~(size_type(0));
186
187 constexpr Span() noexcept : Span(nullptr, 0) {}
188 constexpr Span(pointer array, size_type length) noexcept
189 : ptr_(array), len_(length) {}
190
191 // Implicit conversion constructors
192 template <size_t N>
193 constexpr Span(T (&a)[N]) noexcept // NOLINT(runtime/explicit)
194 : Span(a, N) {}
195
196 // Explicit reference constructor for a mutable `Span<T>` type. Can be
197 // replaced with MakeSpan() to infer the type parameter.
198 template <typename V, typename = EnableIfConvertibleFrom<V>,
199 typename = EnableIfMutableView<V>>
200 explicit Span(V& v) noexcept // NOLINT(runtime/references)
201 : Span(span_internal::GetData(v), v.size()) {}
202
203 // Implicit reference constructor for a read-only `Span<const T>` type
204 template <typename V, typename = EnableIfConvertibleFrom<V>,
205 typename = EnableIfConstView<V>>
206 constexpr Span(const V& v) noexcept // NOLINT(runtime/explicit)
207 : Span(span_internal::GetData(v), v.size()) {}
208
209 // Implicit constructor from an initializer list, making it possible to pass a
210 // brace-enclosed initializer list to a function expecting a `Span`. Such
211 // spans constructed from an initializer list must be of type `Span<const T>`.
212 //
213 // void Process(absl::Span<const int> x);
214 // Process({1, 2, 3});
215 //
216 // Note that as always the array referenced by the span must outlive the span.
217 // Since an initializer list constructor acts as if it is fed a temporary
218 // array (cf. C++ standard [dcl.init.list]/5), it's safe to use this
219 // constructor only when the `std::initializer_list` itself outlives the span.
220 // In order to meet this requirement it's sufficient to ensure that neither
221 // the span nor a copy of it is used outside of the expression in which it's
222 // created:
223 //
224 // // Assume that this function uses the array directly, not retaining any
225 // // copy of the span or pointer to any of its elements.
226 // void Process(absl::Span<const int> ints);
227 //
228 // // Okay: the std::initializer_list<int> will reference a temporary array
229 // // that isn't destroyed until after the call to Process returns.
230 // Process({ 17, 19 });
231 //
232 // // Not okay: the storage used by the std::initializer_list<int> is not
233 // // allowed to be referenced after the first line.
234 // absl::Span<const int> ints = { 17, 19 };
235 // Process(ints);
236 //
237 // // Not okay for the same reason as above: even when the elements of the
238 // // initializer list expression are not temporaries the underlying array
239 // // is, so the initializer list must still outlive the span.
240 // const int foo = 17;
241 // absl::Span<const int> ints = { foo };
242 // Process(ints);
243 //
244 template <typename LazyT = T,
245 typename = EnableIfConstView<LazyT>>
246 Span(
247 std::initializer_list<value_type> v) noexcept // NOLINT(runtime/explicit)
248 : Span(v.begin(), v.size()) {}
249
250 // Accessors
251
252 // Span::data()
253 //
254 // Returns a pointer to the span's underlying array of data (which is held
255 // outside the span).
256 constexpr pointer data() const noexcept { return ptr_; }
257
258 // Span::size()
259 //
260 // Returns the size of this span.
261 constexpr size_type size() const noexcept { return len_; }
262
263 // Span::length()
264 //
265 // Returns the length (size) of this span.
266 constexpr size_type length() const noexcept { return size(); }
267
268 // Span::empty()
269 //
270 // Returns a boolean indicating whether or not this span is considered empty.
271 constexpr bool empty() const noexcept { return size() == 0; }
272
273 // Span::operator[]
274 //
275 // Returns a reference to the i'th element of this span.
276 constexpr reference operator[](size_type i) const noexcept {
277 // MSVC 2015 accepts this as constexpr, but not ptr_[i]
278 return *(data() + i);
279 }
280
281 // Span::at()
282 //
283 // Returns a reference to the i'th element of this span.
284 constexpr reference at(size_type i) const {
285 return ABSL_PREDICT_TRUE(i < size()) //
286 ? *(data() + i)
287 : (base_internal::ThrowStdOutOfRange(
288 "Span::at failed bounds check"),
289 *(data() + i));
290 }
291
292 // Span::front()
293 //
294 // Returns a reference to the first element of this span.
295 constexpr reference front() const noexcept {
296 return ABSL_ASSERT(size() > 0), *data();
297 }
298
299 // Span::back()
300 //
301 // Returns a reference to the last element of this span.
302 constexpr reference back() const noexcept {
303 return ABSL_ASSERT(size() > 0), *(data() + size() - 1);
304 }
305
306 // Span::begin()
307 //
308 // Returns an iterator to the first element of this span.
309 constexpr iterator begin() const noexcept { return data(); }
310
311 // Span::cbegin()
312 //
313 // Returns a const iterator to the first element of this span.
314 constexpr const_iterator cbegin() const noexcept { return begin(); }
315
316 // Span::end()
317 //
318 // Returns an iterator to the last element of this span.
319 constexpr iterator end() const noexcept { return data() + size(); }
320
321 // Span::cend()
322 //
323 // Returns a const iterator to the last element of this span.
324 constexpr const_iterator cend() const noexcept { return end(); }
325
326 // Span::rbegin()
327 //
328 // Returns a reverse iterator starting at the last element of this span.
329 constexpr reverse_iterator rbegin() const noexcept {
330 return reverse_iterator(end());
331 }
332
333 // Span::crbegin()
334 //
335 // Returns a reverse const iterator starting at the last element of this span.
336 constexpr const_reverse_iterator crbegin() const noexcept { return rbegin(); }
337
338 // Span::rend()
339 //
340 // Returns a reverse iterator starting at the first element of this span.
341 constexpr reverse_iterator rend() const noexcept {
342 return reverse_iterator(begin());
343 }
344
345 // Span::crend()
346 //
347 // Returns a reverse iterator starting at the first element of this span.
348 constexpr const_reverse_iterator crend() const noexcept { return rend(); }
349
350 // Span mutations
351
352 // Span::remove_prefix()
353 //
354 // Removes the first `n` elements from the span.
355 void remove_prefix(size_type n) noexcept {
356 assert(size() >= n);
357 ptr_ += n;
358 len_ -= n;
359 }
360
361 // Span::remove_suffix()
362 //
363 // Removes the last `n` elements from the span.
364 void remove_suffix(size_type n) noexcept {
365 assert(size() >= n);
366 len_ -= n;
367 }
368
369 // Span::subspan()
370 //
371 // Returns a `Span` starting at element `pos` and of length `len`. Both `pos`
372 // and `len` are of type `size_type` and thus non-negative. Parameter `pos`
373 // must be <= size(). Any `len` value that points past the end of the span
374 // will be trimmed to at most size() - `pos`. A default `len` value of `npos`
375 // ensures the returned subspan continues until the end of the span.
376 //
377 // Examples:
378 //
379 // std::vector<int> vec = {10, 11, 12, 13};
380 // absl::MakeSpan(vec).subspan(1, 2); // {11, 12}
381 // absl::MakeSpan(vec).subspan(2, 8); // {12, 13}
382 // absl::MakeSpan(vec).subspan(1); // {11, 12, 13}
383 // absl::MakeSpan(vec).subspan(4); // {}
384 // absl::MakeSpan(vec).subspan(5); // throws std::out_of_range
385 constexpr Span subspan(size_type pos = 0, size_type len = npos) const {
386 return (pos <= size())
387 ? Span(data() + pos, span_internal::Min(size() - pos, len))
388 : (base_internal::ThrowStdOutOfRange("pos > size()"), Span());
389 }
390
391 // Span::first()
392 //
393 // Returns a `Span` containing first `len` elements. Parameter `len` is of
394 // type `size_type` and thus non-negative. `len` value must be <= size().
395 //
396 // Examples:
397 //
398 // std::vector<int> vec = {10, 11, 12, 13};
399 // absl::MakeSpan(vec).first(1); // {10}
400 // absl::MakeSpan(vec).first(3); // {10, 11, 12}
401 // absl::MakeSpan(vec).first(5); // throws std::out_of_range
402 constexpr Span first(size_type len) const {
403 return (len <= size())
404 ? Span(data(), len)
405 : (base_internal::ThrowStdOutOfRange("len > size()"), Span());
406 }
407
408 // Span::last()
409 //
410 // Returns a `Span` containing last `len` elements. Parameter `len` is of
411 // type `size_type` and thus non-negative. `len` value must be <= size().
412 //
413 // Examples:
414 //
415 // std::vector<int> vec = {10, 11, 12, 13};
416 // absl::MakeSpan(vec).last(1); // {13}
417 // absl::MakeSpan(vec).last(3); // {11, 12, 13}
418 // absl::MakeSpan(vec).last(5); // throws std::out_of_range
419 constexpr Span last(size_type len) const {
420 return (len <= size())
421 ? Span(size() - len + data(), len)
422 : (base_internal::ThrowStdOutOfRange("len > size()"), Span());
423 }
424
425 // Support for absl::Hash.
426 template <typename H>
427 friend H AbslHashValue(H h, Span v) {
428 return H::combine(H::combine_contiguous(std::move(h), v.data(), v.size()),
429 v.size());
430 }
431
432 private:
433 pointer ptr_;
434 size_type len_;
435};
436
437template <typename T>
438const typename Span<T>::size_type Span<T>::npos;
439
440// Span relationals
441
442// Equality is compared element-by-element, while ordering is lexicographical.
443// We provide three overloads for each operator to cover any combination on the
444// left or right hand side of mutable Span<T>, read-only Span<const T>, and
445// convertible-to-read-only Span<T>.
446// TODO(zhangxy): Due to MSVC overload resolution bug with partial ordering
447// template functions, 5 overloads per operator is needed as a workaround. We
448// should update them to 3 overloads per operator using non-deduced context like
449// string_view, i.e.
450// - (Span<T>, Span<T>)
451// - (Span<T>, non_deduced<Span<const T>>)
452// - (non_deduced<Span<const T>>, Span<T>)
453
454// operator==
455template <typename T>
456bool operator==(Span<T> a, Span<T> b) {
457 return span_internal::EqualImpl<Span, const T>(a, b);
458}
459template <typename T>
460bool operator==(Span<const T> a, Span<T> b) {
461 return span_internal::EqualImpl<Span, const T>(a, b);
462}
463template <typename T>
464bool operator==(Span<T> a, Span<const T> b) {
465 return span_internal::EqualImpl<Span, const T>(a, b);
466}
467template <
468 typename T, typename U,
469 typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
470bool operator==(const U& a, Span<T> b) {
471 return span_internal::EqualImpl<Span, const T>(a, b);
472}
473template <
474 typename T, typename U,
475 typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
476bool operator==(Span<T> a, const U& b) {
477 return span_internal::EqualImpl<Span, const T>(a, b);
478}
479
480// operator!=
481template <typename T>
482bool operator!=(Span<T> a, Span<T> b) {
483 return !(a == b);
484}
485template <typename T>
486bool operator!=(Span<const T> a, Span<T> b) {
487 return !(a == b);
488}
489template <typename T>
490bool operator!=(Span<T> a, Span<const T> b) {
491 return !(a == b);
492}
493template <
494 typename T, typename U,
495 typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
496bool operator!=(const U& a, Span<T> b) {
497 return !(a == b);
498}
499template <
500 typename T, typename U,
501 typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
502bool operator!=(Span<T> a, const U& b) {
503 return !(a == b);
504}
505
506// operator<
507template <typename T>
508bool operator<(Span<T> a, Span<T> b) {
509 return span_internal::LessThanImpl<Span, const T>(a, b);
510}
511template <typename T>
512bool operator<(Span<const T> a, Span<T> b) {
513 return span_internal::LessThanImpl<Span, const T>(a, b);
514}
515template <typename T>
516bool operator<(Span<T> a, Span<const T> b) {
517 return span_internal::LessThanImpl<Span, const T>(a, b);
518}
519template <
520 typename T, typename U,
521 typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
522bool operator<(const U& a, Span<T> b) {
523 return span_internal::LessThanImpl<Span, const T>(a, b);
524}
525template <
526 typename T, typename U,
527 typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
528bool operator<(Span<T> a, const U& b) {
529 return span_internal::LessThanImpl<Span, const T>(a, b);
530}
531
532// operator>
533template <typename T>
534bool operator>(Span<T> a, Span<T> b) {
535 return b < a;
536}
537template <typename T>
538bool operator>(Span<const T> a, Span<T> b) {
539 return b < a;
540}
541template <typename T>
542bool operator>(Span<T> a, Span<const T> b) {
543 return b < a;
544}
545template <
546 typename T, typename U,
547 typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
548bool operator>(const U& a, Span<T> b) {
549 return b < a;
550}
551template <
552 typename T, typename U,
553 typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
554bool operator>(Span<T> a, const U& b) {
555 return b < a;
556}
557
558// operator<=
559template <typename T>
560bool operator<=(Span<T> a, Span<T> b) {
561 return !(b < a);
562}
563template <typename T>
564bool operator<=(Span<const T> a, Span<T> b) {
565 return !(b < a);
566}
567template <typename T>
568bool operator<=(Span<T> a, Span<const T> b) {
569 return !(b < a);
570}
571template <
572 typename T, typename U,
573 typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
574bool operator<=(const U& a, Span<T> b) {
575 return !(b < a);
576}
577template <
578 typename T, typename U,
579 typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
580bool operator<=(Span<T> a, const U& b) {
581 return !(b < a);
582}
583
584// operator>=
585template <typename T>
586bool operator>=(Span<T> a, Span<T> b) {
587 return !(a < b);
588}
589template <typename T>
590bool operator>=(Span<const T> a, Span<T> b) {
591 return !(a < b);
592}
593template <typename T>
594bool operator>=(Span<T> a, Span<const T> b) {
595 return !(a < b);
596}
597template <
598 typename T, typename U,
599 typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
600bool operator>=(const U& a, Span<T> b) {
601 return !(a < b);
602}
603template <
604 typename T, typename U,
605 typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
606bool operator>=(Span<T> a, const U& b) {
607 return !(a < b);
608}
609
610// MakeSpan()
611//
612// Constructs a mutable `Span<T>`, deducing `T` automatically from either a
613// container or pointer+size.
614//
615// Because a read-only `Span<const T>` is implicitly constructed from container
616// types regardless of whether the container itself is a const container,
617// constructing mutable spans of type `Span<T>` from containers requires
618// explicit constructors. The container-accepting version of `MakeSpan()`
619// deduces the type of `T` by the constness of the pointer received from the
620// container's `data()` member. Similarly, the pointer-accepting version returns
621// a `Span<const T>` if `T` is `const`, and a `Span<T>` otherwise.
622//
623// Examples:
624//
625// void MyRoutine(absl::Span<MyComplicatedType> a) {
626// ...
627// };
628// // my_vector is a container of non-const types
629// std::vector<MyComplicatedType> my_vector;
630//
631// // Constructing a Span implicitly attempts to create a Span of type
632// // `Span<const T>`
633// MyRoutine(my_vector); // error, type mismatch
634//
635// // Explicitly constructing the Span is verbose
636// MyRoutine(absl::Span<MyComplicatedType>(my_vector));
637//
638// // Use MakeSpan() to make an absl::Span<T>
639// MyRoutine(absl::MakeSpan(my_vector));
640//
641// // Construct a span from an array ptr+size
642// absl::Span<T> my_span() {
643// return absl::MakeSpan(&array[0], num_elements_);
644// }
645//
646template <int&... ExplicitArgumentBarrier, typename T>
647constexpr Span<T> MakeSpan(T* ptr, size_t size) noexcept {
648 return Span<T>(ptr, size);
649}
650
651template <int&... ExplicitArgumentBarrier, typename T>
652Span<T> MakeSpan(T* begin, T* end) noexcept {
653 return ABSL_ASSERT(begin <= end), Span<T>(begin, end - begin);
654}
655
656template <int&... ExplicitArgumentBarrier, typename C>
657constexpr auto MakeSpan(C& c) noexcept // NOLINT(runtime/references)
658 -> decltype(absl::MakeSpan(span_internal::GetData(c), c.size())) {
659 return MakeSpan(span_internal::GetData(c), c.size());
660}
661
662template <int&... ExplicitArgumentBarrier, typename T, size_t N>
663constexpr Span<T> MakeSpan(T (&array)[N]) noexcept {
664 return Span<T>(array, N);
665}
666
667// MakeConstSpan()
668//
669// Constructs a `Span<const T>` as with `MakeSpan`, deducing `T` automatically,
670// but always returning a `Span<const T>`.
671//
672// Examples:
673//
674// void ProcessInts(absl::Span<const int> some_ints);
675//
676// // Call with a pointer and size.
677// int array[3] = { 0, 0, 0 };
678// ProcessInts(absl::MakeConstSpan(&array[0], 3));
679//
680// // Call with a [begin, end) pair.
681// ProcessInts(absl::MakeConstSpan(&array[0], &array[3]));
682//
683// // Call directly with an array.
684// ProcessInts(absl::MakeConstSpan(array));
685//
686// // Call with a contiguous container.
687// std::vector<int> some_ints = ...;
688// ProcessInts(absl::MakeConstSpan(some_ints));
689// ProcessInts(absl::MakeConstSpan(std::vector<int>{ 0, 0, 0 }));
690//
691template <int&... ExplicitArgumentBarrier, typename T>
692constexpr Span<const T> MakeConstSpan(T* ptr, size_t size) noexcept {
693 return Span<const T>(ptr, size);
694}
695
696template <int&... ExplicitArgumentBarrier, typename T>
697Span<const T> MakeConstSpan(T* begin, T* end) noexcept {
698 return ABSL_ASSERT(begin <= end), Span<const T>(begin, end - begin);
699}
700
701template <int&... ExplicitArgumentBarrier, typename C>
702constexpr auto MakeConstSpan(const C& c) noexcept -> decltype(MakeSpan(c)) {
703 return MakeSpan(c);
704}
705
706template <int&... ExplicitArgumentBarrier, typename T, size_t N>
707constexpr Span<const T> MakeConstSpan(const T (&array)[N]) noexcept {
708 return Span<const T>(array, N);
709}
710} // namespace absl
711#endif // ABSL_TYPES_SPAN_H_
712