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https://github.com/martinmoene/span-lite

span lite - A C++20-like span for C++98, C++11 and later in a single-file header-only library
https://github.com/martinmoene/span-lite
cpp11 cpp14 cpp17 cpp20 cpp98 header-only no-dependencies single-file span span-implementation
Last synced: 27 days ago
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span lite - A C++20-like span for C++98, C++11 and later in a single-file header-only library
Host: GitHub
URL: https://github.com/martinmoene/span-lite
Owner: martinmoene
License: bsl-1.0
Created: 2018-03-31T18:43:22.000Z (over 6 years ago)
Default Branch: master
Last Pushed: 2024-06-04T08:08:41.000Z (5 months ago)
Last Synced: 2024-09-28T23:40:57.570Z (about 1 month ago)
Topics: cpp11, cpp14, cpp17, cpp20, cpp98, header-only, no-dependencies, single-file, span, span-implementation
Language: C++
Homepage:
Size: 396 KB
Stars: 498
Watchers: 18
Forks: 41
Open Issues: 8
Metadata Files:
- Readme: README.md
- License: LICENSE.txt
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AwesomeCppGameDev - span-lite - A C++20-like span for C++98, C++11 and later in a single-file header-only library (C++)
README

        

# span lite: A single-file header-only version of a C++20-like span for C++98, C++11 and later

[![Language](https://img.shields.io/badge/C%2B%2B-98/11/14/17/20-blue.svg)](https://en.wikipedia.org/wiki/C%2B%2B#Standardization) [![License](https://img.shields.io/badge/license-BSL-blue.svg)](https://opensource.org/licenses/BSL-1.0) [![Build Status](https://github.com/martinmoene/span-lite/actions/workflows/ci.yml/badge.svg)](https://github.com/martinmoene/span-lite/actions/workflows/ci.yml) [![Build status](https://ci.appveyor.com/api/projects/status/1ha3wnxtam547m8p?svg=true)](https://ci.appveyor.com/project/martinmoene/span-lite) [![Version](https://badge.fury.io/gh/martinmoene%2Fspan-lite.svg)](https://github.com/martinmoene/span-lite/releases) [![download](https://img.shields.io/badge/latest-download-blue.svg)](https://github.com/martinmoene/span-lite/blob/master/include/nonstd/span.hpp) [![Conan](https://img.shields.io/badge/on-conan-blue.svg)](https://conan.io/center/span-lite) [![Vcpkg](https://img.shields.io/badge/on-vcpkg-blue.svg)](https://vcpkg.link/ports/span-lite) [![Try it on wandbox](https://img.shields.io/badge/on-wandbox-blue.svg)](https://wandbox.org/permlink/venR3Ko2Q4tlvcVk) [![Try it on godbolt online](https://img.shields.io/badge/on-godbolt-blue.svg)](https://godbolt.org/z/htwpnb)

**Contents**  

- [Example usage](#example-usage)

- [In a nutshell](#in-a-nutshell)

- [License](#license)

- [Dependencies](#dependencies)

- [Installation and use](#installation-and-use)

- [Synopsis](#synopsis)

- [Reported to work with](#reported-to-work-with)

- [Building the tests](#building-the-tests)

- [Other implementations of span](#other-implementations-of-span)

- [Notes and references](#notes-and-references)

- [Appendix](#appendix)

## Example usage

```cpp

#include "nonstd/span.hpp"

#include 

#include 

#include 

std::ptrdiff_t size( nonstd::span spn )

{

    return spn.size();

}

int main()

{

    int arr[] = { 1, };

    std::cout << 

        "C-array:" << size( arr ) <<

        " array:"  << size( std::array { 1, 2, } ) <<

        " vector:" << size( std::vector{ 1, 2, 3, } );

}

```

### Compile and run

```bash

prompt> g++ -std=c++11 -Wall -I../include -o 01-basic.exe 01-basic.cpp && 01-basic.exe

C-array:1 array:2 vector:3

```

## In a nutshell

**span lite** is a single-file header-only library to provide a bounds-safe view for sequences of objects. The library provides a [C++20-like span](http://en.cppreference.com/w/cpp/container/span) for use with C++98 and later. If available, `std::span` is used, unless [configured otherwise](#configuration). *span-lite* can detect the presence of [*byte-lite*](https://github.com/martinmoene/byte-lite) and if present, it provides `as_bytes()` and `as_writable_bytes()` also for C++14 and earlier. 

**Features and properties of span lite** are ease of installation (single header), freedom of dependencies other than the standard library. To compensate for the class template argument deduction that is missing from pre-C++17 compilers, `nonstd::span` can provide `make_span` functions. See [configuration](#configuration).

## License

*span lite* is distributed under the [Boost Software License](https://github.com/martinmoene/span-lite/blob/master/LICENSE.txt).

## Dependencies

*span lite* has no other dependencies than the [C++ standard library](http://en.cppreference.com/w/cpp/header).

## Installation and use

*span lite* is a single-file header-only library. Put `span.hpp` in the [include](include) folder directly into the project source tree or somewhere reachable from your project.

## Synopsis

**Contents**  

[Documentation of `std::span`](#documentation-of-stdspan)  

[Later additions](#later-additions)  

[Non-standard extensions](#non-standard-extensions)  

[Configuration](#configuration)  

## Documentation of `std::span`

Depending on the compiler and C++-standard used, `nonstd::span` behaves less or more like `std::span`. To get an idea of the capabilities of `nonstd::span` with your configuration, look at the output of the [tests](test/span.t.cpp), issuing `span-main.t --pass @`. For `std::span`, see its [documentation at cppreference](http://en.cppreference.com/w/cpp/container/span).  

## Later additions

### `back()` and `front()`

*span lite* can provide `back()` and `front()` member functions for element access. See the table below and section [configuration](#configuration).

## Non-standard extensions

### Construct from std::initializer_list (p2447)

*span lite* can provide construction from a std::initializer_list<> as a constant set of values as proposed in [p2447](https://wg21.link/p2447). See the table below and section [configuration](#configuration).

### Construct from container

To construct a span from a container with compilers that cannot constrain such a single-parameter constructor to containers, *span lite* provides a constructor that takes an additional parameter of type `with_container_t`. Use `with_container` as value for this parameter. See the table below and section [configuration](#configuration).

### Construct from `std::array` with const data

*span lite* can provide construction of a span from a `std::array` with const data. See the table below and section [configuration](#configuration).

### `operator()`

*span lite* can provide member function call `operator()` for element access. It is equivalent to `operator[]` and has been marked `[[deprecated]]`. Its main purpose is to provide a migration path. 

### `at()`

*span lite* can provide member function `at()` for element access. Unless exceptions have been disabled, `at()` throws std::out_of_range if the index falls outside the span. With exceptions disabled, `at(index_t)` delegates bounds checking to `operator[](index_t)`. See the table below and sections [configuration](#configuration) and [disable exceptions](#disable-exceptions).

### `swap()`

*span lite* can provide a `swap()`member function. See the table below and section [configuration](#configuration).

### `operator==()` and other comparison functions

*span lite* can provide functions to compare the content of two spans. However, C++20's span will not provide comparison and _span lite_ will omit comparison at default in the near future. See the table below and section [configuration](#configuration). See also [Revisiting Regular Types](#regtyp).

### `same()`

*span lite* can provide function `same()` to determine if two spans refer as identical spans to the same data via the same type. If `same()` is enabled, `operator==()` incorporates it in its comparison. See the table below and section [configuration](#configuration).

### `first()`, `last()` and `subspan()`

*span lite* can provide functions `first()`, `last()` and `subspan()` to avoid having to use the *dot template* syntax when the span is a dependent type. See the table below and section [configuration](#configuration).

### `make_span()`

*span lite* can provide `make_span()` creator functions to compensate for the class template argument deduction that is missing from pre-C++17 compilers. See the table below and section [configuration](#configuration).

### `byte_span()`

*span lite* can provide `byte_span()` creator functions to represent an object as a span of bytes. This requires the C++17 type `std::byte` to be available. See the table below and section [configuration](#configuration).

| Kind               | std  | Function or method |

|--------------------|------|--------------------|

| **Macro**          | | macro **`span_FEATURE_WITH_INITIALIZER_LIST_P2447`** |

| **Constructor**
  | | constexpr explicit **span**( std::initializer_list<value_type> il ) noexcept
explicit for non-dynamic extent |

|               | |   |

| **Macro**
 | | macro **`span_FEATURE_WITH_CONTAINER`**
macro **`span_FEATURE_WITH_CONTAINER_TO_STD`** |

| **Types**          | | **with_container_t** type to disambiguate below constructors |

| **Objects**        | | **with_container** value to disambiguate below constructors |

| **Constructors**   | | macro **`span_FEATURE_CONSTRUCTION_FROM_STDARRAY_ELEMENT_TYPE`**|

|               | | template<class Container>
constexpr **span**(with_container_t, Container & cont) |

|               | | template<class Container>
constexpr **span**(with_container_t, Container const & cont) |

|               | |   |

| **Methods**        | | macro **`span_FEATURE_MEMBER_CALL_OPERATOR`** |

|               | | constexpr reference **operator()**(index_t idx) const
Equivalent to **operator[]**(), marked `[[deprecated]]` |

|               | |   |

| **Methods**        | | macro **`span_FEATURE_MEMBER_AT`** |

|               | | constexpr reference **at**(index_t idx) const
May throw std::out_of_range exception |

|               | |   |

| **Methods**        | | macro **`span_FEATURE_MEMBER_BACK_FRONT`** (on since v0.5.0) |

|               | | constexpr reference **back()** const noexcept  |

|               | | constexpr reference **front()** const noexcept |

|               | |   |

| **Method**         | | macro **`span_FEATURE_MEMBER_SWAP`** |

|               | | constexpr void **swap**(span & other) noexcept  |

|               | |   |

| **Free functions** | | macro **`span_FEATURE_COMPARISON`** |

|

== != < > <= >= | | template<class T1, index_t E1, class T2, index_t E2>
constexpr bool
**operator==**( span const & l, span const & r) noexcept |

|               | |   |

| **Free function**  | | macro **`span_FEATURE_SAME`** |

|               | | template<class T1, index_t E1, class T2, index_t E2>
constexpr bool
**same**( span const & l, span const & r) noexcept |

|               | |   |

| **Free functions**
 
  | | macros **`span_FEATURE_NON_MEMBER_FIRST_LAST_SUB`**,
**`span_FEATURE_NON_MEMBER_FIRST_LAST_SUB_SPAN`**,
**`span_FEATURE_NON_MEMBER_FIRST_LAST_SUB_CONTAINER`** |

|               | |   |

| **Free functions** | | macro **`span_FEATURE_NON_MEMBER_FIRST_LAST_SUB_SPAN`** |

|   |      | template<extent_t Count, class T, extent_t Extent>
constexpr span<T,Count>
**first**(span<T,Extent> spn) |

|   |      | template<class T, extent_t Extent >
constexpr span<T>
**first**(span<T,Extent> spn, size_t count) |

|   |      | template<extent_t Count, class T, extent_t Extent>
constexpr span<T,Count>
**last**(span<T,Extent> spn) |

|   |      | template<class T, extent_t Extent >
constexpr span<T>
**last**(span<T,Extent> spn, size_t count) |

|   |      | template<size_t Offset, extent_t Count, class T, extent_t Extent>
constexpr span<T, Count>
**subspan**(span<T, Extent> spn) |

|   |      | template<class T, extent_t Extent>
constexpr span<T>
**subspan**( span<T, Extent> spn, size_t offset, extent_t count = dynamic_extent) |

|               | |   |

| **Free functions** | | macro **`span_FEATURE_NON_MEMBER_FIRST_LAST_SUB_CONTAINER`** |

|   | >= C++11  | template<extent_t Count, class T>
constexpr auto
**first**(T & t) ->... |

|   | >= C++11  | template<class T>
constexpr auto
**first**(T & t, index_t count) ->... |

|   | >= C++11  | template<extent_t Count, class T>
constexpr auto
**last**(T & t) ->... |

|   | >= C++11  | template<class T>
constexpr auto
**last**(T & t, extent_t count) ->... |

|   | >= C++11  | template<index_t Offset, extent_t Count = dynamic_extent, class T>
constexpr auto
**subspan**(T & t) ->... |

|   | >= C++11  | template<class T>
constexpr auto
**subspan**(T & t, index_t offset, extent_t count = dynamic_extent) ->... |

|   |      |   |

| **Free functions**
  | | macro **`span_FEATURE_MAKE_SPAN`**
macro **`span_FEATURE_MAKE_SPAN_TO_STD`** |

|   |      | template<class T>
constexpr span<T>
**make_span**(T \* first, T \* last) noexcept |

|   |      | template<class T>
constexpr span<T>
**make_span**(T \* ptr, index_t count) noexcept |

|   |      | template<class T, size_t N>
constexpr span<T,N>
**make_span**(T (&arr)[N]) noexcept |

|   | >= C++11  | template<class T, size_t N>
constexpr span<T,N>
**make_span**(std::array<T,N> & arr) noexcept |

|   | >= C++11  | template<class T, size_t N>
constexpr span<const T,N>
**make_span**(std::array<T,N > const & arr) noexcept |

|   | >= C++11  | template<class T>
constexpr span<T>
**make_span**(std::initializer_list<T> il) noexcept |

|   | >= C++11  | template<class Container>
constexpr auto
**make_span**(Container & cont) ->
 span<typename Container::value_type> noexcept |

|   | >= C++11  | template<class Container>
constexpr auto
**make_span**(Container const & cont) ->
 span<const typename Container::value_type> noexcept |

|   |      | template<class Container>
span<typename Container::value_type>
**make_span**( with_container_t, Container & cont ) |

|   |      | template<class Container>
span<const typename Container::value_type>
**make_span**( with_container_t, Container const & cont ) |

|   | < C++11   | template<class T, Allocator>
span<T>
**make_span**(std::vector<T, Allocator> & cont) |

|   | < C++11   | template<class T, Allocator>
span<const T>
**make_span**(std::vector<T, Allocator> const & cont) |

|   |      |   |                                       

| **Free functions** | | macro **`span_FEATURE_BYTE_SPAN`** |

|   | >= C++11  | template<class T>
span<T, sizeof(T)>
**byte_span**(T & t) |

|   | >= C++11  | template<class T>
span<const T, sizeof(T)>
**byte_span**(T const & t) |

## Configuration

### Tweak header

If the compiler supports [`__has_include()`](https://en.cppreference.com/w/cpp/preprocessor/include), *span lite* supports the [tweak header](https://vector-of-bool.github.io/2020/10/04/lib-configuration.html) mechanism. Provide your *tweak header* as `nonstd/span.tweak.hpp` in a folder in the include-search-path. In the tweak header, provide definitions as documented below, like `#define span_CONFIG_NO_EXCEPTIONS 1`.

### Standard selection macro

\-Dspan\_CPLUSPLUS=199711L  

Define this macro to override the auto-detection of the supported C++ standard, if your compiler does not set the `__cplusplus` macro correctly.

### Select `std::span` or `nonstd::span`

At default, *span lite* uses `std::span` if it is available and lets you use it via namespace `nonstd`. You can however override this default and explicitly request to use `std::span` or span lite's `nonstd::span` as `nonstd::span` via the following macros.

-Dspan\_CONFIG\_SELECT\_SPAN=span_SPAN_DEFAULT  

Define this to `span_SPAN_STD` to select `std::span` as `nonstd::span`. Define this to `span_SPAN_NONSTD` to select `nonstd::span` as `nonstd::span`. Default is undefined, which has the same effect as defining to `span_SPAN_DEFAULT`.

### Select extent type

-Dspan_CONFIG_EXTENT_TYPE=std::size_t  

Define this to `std::ptrdiff_t` to use the signed type. The default is `std::size_t`, as in C++20 (since v0.7.0).

### Select size type

-Dspan_CONFIG_SIZE_TYPE=std::size_t  

Define this to `std::ptrdiff_t` to use the signed type. The default is `std::size_t`, as in C++20 (since v0.7.0). Note `span_CONFIG_SIZE_TYPE` replaces `span_CONFIG_INDEX_TYPE` which is deprecated.

### Disable exceptions

-Dspan_CONFIG_NO_EXCEPTIONS=0  

Define this to 1 if you want to compile without exceptions. If not defined, the header tries and detect if exceptions have been disabled (e.g. via `-fno-exceptions`). Disabling exceptions will force contract violation to use termination, see [contract violation macros](#contract-violation-response-macros). Default is undefined.

### Provide construction from std::initializer_list (p2447)

-Dspan_FEATURE_WITH_INITIALIZER_LIST_P2447=0  

Define this to 1 to enable constructing a span from a std::initializer_list<> as a constant set of values. See proposal [p2447](https://wg21.link/p2447). Default is undefined.

### Provide construction using `with_container_t`

-Dspan_FEATURE_WITH_CONTAINER=0  

Define this to 1 to enable constructing a span using `with_container_t`. Note that `span_FEATURE_WITH_CONTAINER` takes precedence over `span_FEATURE_WITH_CONTAINER_TO_STD`. Default is undefined.

-Dspan_FEATURE_WITH_CONTAINER_TO_STD=*n*  

Define this to the highest C++ language version for which to enable constructing a span using `with_container_t`, like 98, 03, 11, 14, 17, 20. You can use 99 for inclusion with any standard, but prefer to use `span_FEATURE_WITH_CONTAINER` for this. Note that `span_FEATURE_WITH_CONTAINER` takes precedence over `span_FEATURE_WITH_CONTAINER_TO_STD`. Default is undefined.

### Provide construction from `std::array` with const data

-Dspan_FEATURE_CONSTRUCTION_FROM_STDARRAY_ELEMENT_TYPE=0  

Define this to 1 to enable constructing a span from a std::array with const data. Default is undefined.

### Provide `operator()` member function

-Dspan_FEATURE_MEMBER_CALL_OPERATOR=0  

Define this to 1 to provide member function `operator()`for element access. It is equivalent to `operator[]` and has been marked `[[deprecated]]`. Its main purpose is to provide a migration path. Default is undefined.

### Provide `at()` member function

-Dspan_FEATURE_MEMBER_AT=0  

Define this to 1 to provide member function `at()`. Define this to 2 to include index and size in message of std::out_of_range exception. Default is undefined.

### Provide `back()` and `front()` member functions

-Dspan_FEATURE_MEMBER_BACK_FRONT=1  _(on since v0.5.0)_  

Define this to 0 to omit member functions `back()` and `front()`. Default is undefined.

### Provide `swap()` member function

-Dspan_FEATURE_MEMBER_SWAP=0  

Define this to 1 to provide member function `swap()`. Default is undefined.

### Provide `operator==()` and other comparison functions

-Dspan_FEATURE_COMPARISON=0  

Define this to 1 to include the comparison functions to compare the content of two spans. C++20's span does not provide comparison and _span lite_ omits comparison from v0.7.0. Default is undefined.

### Provide `same()` function

-Dspan_FEATURE_SAME=0  

Define this to 1 to provide function `same()` to test if two spans refer as identical spans to the same data via the same type. If `same()` is enabled, `operator==()` incorporates it in its comparison. Default is undefined.

### Provide `first()`, `last()` and `subspan()` functions

-Dspan_FEATURE_NON_MEMBER_FIRST_LAST_SUB=0  

Define this to 1 to enable both `span_FEATURE_NON_MEMBER_FIRST_LAST_SUB_SPAN` and `span_FEATURE_NON_MEMBER_FIRST_LAST_SUB_CONTAINER`. Default is undefined.

-Dspan_FEATURE_NON_MEMBER_FIRST_LAST_SUB_SPAN=0  

Define this to 1 to provide functions `first()`, `last()` and `subspan()` that take a `span<>` (work with C++98). This implies `span_FEATURE_MAKE_SPAN` to provide functions `make_span()` that are required for this feature. Default is undefined.

-Dspan_FEATURE_NON_MEMBER_FIRST_LAST_SUB_CONTAINER=0  

Define this to 1 to provide functions `first()`, `last()` and `subspan()` that take a compatible container (requires C++11). This implies `span_FEATURE_MAKE_SPAN` to provide functions `make_span()` that are required for this feature. Default is undefined.

### Provide `make_span()` functions

-Dspan_FEATURE_MAKE_SPAN=0  

Define this to 1 to provide creator functions `nonstd::make_span()`. This feature is implied by using `span_FEATURE_NON_MEMBER_FIRST_LAST_SUB=1`. Note that `span_FEATURE_MAKE_SPAN` takes precedence over `span_FEATURE_MAKE_SPAN_TO_STD`. Default is undefined.

-Dspan_FEATURE_MAKE_SPAN_TO_STD=*n*  

Define this to the highest C++ language version for which to provide creator functions `nonstd::make_span()`, like 98, 03, 11, 14, 17, 20. You can use 99 for inclusion with any standard, but prefer to use `span_FEATURE_MAKE_SPAN` for this. Note that `span_FEATURE_MAKE_SPAN` takes precedence over `span_FEATURE_MAKE_SPAN_TO_STD`. Default is undefined.

### Provide `byte_span()` functions

-Dspan_FEATURE_BYTE_SPAN=0  

Define this to 1 to provide creator functions `nonstd::byte_span()`. Default is undefined.

### Contract violation response macros

*span-lite* provides contract violation response control as suggested in proposal [N4415](http://wg21.link/n4415).

\-Dspan\_CONFIG\_CONTRACT\_LEVEL\_ON  (*default*)  

Define this macro to include both `span_EXPECTS` and `span_ENSURES` in the code. This is the default case.

\-Dspan\_CONFIG\_CONTRACT\_LEVEL\_OFF  

Define this macro to exclude both `span_EXPECTS` and `span_ENSURES` from the code.

\-Dspan\_CONFIG_CONTRACT\_LEVEL\_EXPECTS\_ONLY  

Define this macro to include `span_EXPECTS` in the code and exclude `span_ENSURES` from the code.

\-Dspan\_CONFIG\_CONTRACT\_LEVEL\_ENSURES\_ONLY  

Define this macro to exclude `span_EXPECTS` from the code and include `span_ENSURES` in the code.

\-Dspan\_CONFIG\_CONTRACT\_VIOLATION\_TERMINATES  (*default*)  

Define this macro to call `std::terminate()` on a contract violation in `span_EXPECTS`, `span_ENSURES`. This is the default case.

\-Dspan\_CONFIG\_CONTRACT\_VIOLATION\_THROWS  

Define this macro to throw an exception of implementation-defined type that is derived from `std::runtime_exception` instead of calling `std::terminate()` on a contract violation in `span_EXPECTS` and `span_ENSURES`. See also [disable exceptions](#disable-exceptions).

Reported to work with

--------------------

The table below mentions the compiler versions *span lite* is reported to work with.

OS           | Compiler   | Where   | Versions |

------------:|:-----------|:--------|:---------|

**GNU/Linux**| Clang/LLVM | Travis  | 3.5.0, 3.6.2, 3.7.1, 3.8.0, 3.9.1, 4.0.1  |

        | GCC        | Travis  | 5.5.0, 6.4.0, 7.3.0 |

**OS X**     | ?          | Local   | ?        |

**Windows**  | Clang/LLVM | Local   | 6.0.0    |

        | GCC        | Local   | 7.2.0    |

        | Visual C++
(Visual Studio)| Local | 8 (2005), 10 (2010), 11 (2012),
12 (2013), 14 (2015), 15 (2017) |

        | Visual C++
(Visual Studio)| AppVeyor | 10 (2010), 11 (2012),
12 (2013), 14 (2015), 15 (2017) |

## Building the tests

To build the tests you need:

- [CMake](http://cmake.org), version 3.0 or later to be installed and in your PATH.

- A [suitable compiler](#reported-to-work-with).

The [*lest* test framework](https://github.com/martinmoene/lest) is included in the [test folder](test).

The following steps assume that the [*span lite* source code](https://github.com/martinmoene/span-lite) has been cloned into a directory named `./span-lite`.

1. Create a directory for the build outputs.

        cd ./span-lite

        md build && cd build

2. Configure CMake to use the compiler of your choice (run `cmake --help` for a list).

        cmake -G "Unix Makefiles" -DSPAN_LITE_OPT_BUILD_TESTS=ON ..

3. Optional. You can control above configuration through the following options:

    `-DSPAN_LITE_OPT_BUILD_TESTS=ON`: build the tests for span, default off  

    `-DSPAN_LITE_OPT_BUILD_EXAMPLES=OFF`: build the examples, default off  

4. Build the test suite.

        cmake --build .

5. Run the test suite.

        ctest -V

All tests should pass, indicating your platform is supported and you are ready to use *span lite*.

## Other implementations of span

- *gsl-lite* [span](https://github.com/martinmoene/gsl-lite/blob/73c4f16f2b35fc174fc2f09d44d5ab13e5c638c3/include/gsl/gsl-lite.hpp#L1221).

- Microsoft GSL [span](https://github.com/Microsoft/GSL/blob/master/include/gsl/span).

- Google Abseil [span](https://github.com/abseil/abseil-cpp/blob/master/absl/types/span.h).

- Marshall Clow's [libc++ span snippet](https://github.com/mclow/snippets/blob/master/span.cpp).

- Tristan Brindle's [Implementation of C++20's std::span for older compilers](https://github.com/tcbrindle/span).

- [Search _span c++_ on GitHub](https://github.com/search?l=C%2B%2B&q=span+c%2B%2B&type=Repositories&utf8=%E2%9C%93).

## Notes and references

*Interface and specification*

- [span on cppreference](https://en.cppreference.com/w/cpp/container/span).

- [p0122 - C++20 Proposal](http://wg21.link/p0122).

- [span in C++20 Working Draft](http://eel.is/c++draft/views).

*Presentations*

- TBD

*Proposals*

- [p0122 - span: bounds-safe views for sequences of objects](http://wg21.link/p0122).

- [p1024 - Usability Enhancements for std::span](http://wg21.link/p1024).

- [p1419 - A SFINAE-friendly trait to determine the extent of statically sized containers](http://wg21.link/p1419).  

- [p0805 - Comparing Containers](http://wg21.link/p0805).

- [p1085 - Should Span be Regular?](http://wg21.link/p0805).

- [p0091 - Template argument deduction for class templates](http://wg21.link/p0091).

- [p0856 - Restrict Access Property for mdspan and span](http://wg21.link/p0856).

- [p1428 - Subscripts and sizes should be signed](http://wg21.link/p1428).

- [p1089 - Sizes Should Only span Unsigned](http://wg21.link/p1089).

- [p1227 - Signed size() functions](http://wg21.link/p1227).

- [p1872 - span should have size_type, not index_type](http://wg21.link/p1872).

- [p2447 - std::span and the missing constructor](https://wg21.link/p2447).

- [lwg 3101 - span's Container constructors need another constraint](https://cplusplus.github.io/LWG/issue3101).

- [Reddit - 2018-06 Rapperswil ISO C++ Committee Trip Report](https://www.reddit.com/r/cpp/comments/8prqzm/2018_rapperswil_iso_c_committee_trip_report/)

- [Reddit - 2018-11 San Diego ISO C++ Committee Trip Report](https://www.reddit.com/r/cpp/comments/9vwvbz/2018_san_diego_iso_c_committee_trip_report_ranges/).

- [Reddit - 2019-02 Kona ISO C++ Committee Trip Report](https://www.reddit.com/r/cpp/comments/au0c4x/201902_kona_iso_c_committee_trip_report_c20/).

- [Reddit - 2019-07 Cologne ISO C++ Committee Trip Report](https://www.reddit.com/r/cpp/comments/cfk9de/201907_cologne_iso_c_committee_trip_report_the/)

- [Reddit - 2019-11 Belfast ISO C++ Committee Trip Report](https://www.reddit.com/r/cpp/comments/dtuov8/201911_belfast_iso_c_committee_trip_report/)

- Titus Winters. [Revisiting Regular Types](https://abseil.io/blog/20180531-regular-types). Abseil Blog. 31 May 2018.

## Appendix

### A.1 Compile-time information

The version of *span lite* is available via tag `[.version]`. The following tags are available for information on the compiler and on the C++ standard library used: `[.compiler]`, `[.stdc++]`, `[.stdlanguage]` and `[.stdlibrary]`.

### A.2 Span lite test specification

click to expand



```Text

span<>: Terminates construction from a nullptr and a non-zero size (C++11)

span<>: Terminates construction from two pointers in the wrong order

span<>: Terminates construction from a null pointer and a non-zero size

span<>: Terminates creation of a sub span of the first n elements for n exceeding the span

span<>: Terminates creation of a sub span of the last n elements for n exceeding the span

span<>: Terminates creation of a sub span outside the span

span<>: Terminates access outside the span

span<>: Throws  on access outside the span via at(): std::out_of_range [span_FEATURE_MEMBER_AT>0][span_CONFIG_NO_EXCEPTIONS=0]

span<>: Termination throws std::logic_error-derived exception [span_CONFIG_CONTRACT_VIOLATION_THROWS=1]

span<>: Allows to default-construct

span<>: Allows to construct from a nullptr and a zero size (C++11)

span<>: Allows to construct from two pointers

span<>: Allows to construct from two iterators

span<>: Allows to construct from two iterators - empty range

span<>: Allows to construct from two iterators - move-only element

span<>: Allows to construct from an iterator and a size

span<>: Allows to construct from an iterator and a size - empty range

span<>: Allows to construct from an iterator and a size - move-only element

span<>: Allows to construct from two pointers to const

span<>: Allows to construct from a non-null pointer and a size

span<>: Allows to construct from a non-null pointer to const and a size

span<>: Allows to construct from a temporary pointer and a size

span<>: Allows to construct from a temporary pointer to const and a size

span<>: Allows to construct from any pointer and a zero size (C++98)

span<>: Allows to construct from a pointer and a size via a deduction guide (C++17)

span<>: Allows to construct from an iterator and a size via a deduction guide (C++17)

span<>: Allows to construct from two iterators via a deduction guide (C++17)

span<>: Allows to construct from a C-array

span<>: Allows to construct from a C-array via a deduction guide (C++17)

span<>: Allows to construct from a const C-array

span<>: Allows to construct from a C-array with size via decay to pointer (potentially dangerous)

span<>: Allows to construct from a const C-array with size via decay to pointer (potentially dangerous)

span<>: Allows to construct from a std::initializer_list<> (C++11)

span<>: Allows to construct from a std::initializer_list<> as a constant set of values (C++11, p2447)

span<>: Allows to construct from a std::array<> (C++11)

span<>: Allows to construct from a std::array via a deduction guide (C++17)

span<>: Allows to construct from a std::array<> with const data (C++11, span_FEATURE_CONSTR..._ELEMENT_TYPE=1)

span<>: Allows to construct from an empty std::array<> (C++11)

span<>: Allows to construct from a container (std::vector<>)

span<>: Allows to construct from a container via a deduction guide (std::vector<>, C++17)

span<>: Allows to tag-construct from a container (std::vector<>)

span<>: Allows to tag-construct from a const container (std::vector<>)

span<>: Allows to copy-construct from another span of the same type

span<>: Allows to copy-construct from another span of a compatible type

span<>: Allows to copy-construct from a temporary span of the same type (C++11)

span<>: Allows to copy-assign from another span of the same type

span<>: Allows to copy-assign from a temporary span of the same type (C++11)

span<>: Allows to create a sub span of the first n elements

span<>: Allows to create a sub span of the last n elements

span<>: Allows to create a sub span starting at a given offset

span<>: Allows to create a sub span starting at a given offset with a given length

span<>: Allows to observe an element via array indexing

span<>: Allows to observe an element via call indexing

span<>: Allows to observe an element via at() [span_FEATURE_MEMBER_AT>0]

span<>: Allows to observe an element via data()

span<>: Allows to observe the first element via front() [span_FEATURE_MEMBER_BACK_FRONT=1]

span<>: Allows to observe the last element via back() [span_FEATURE_MEMBER_BACK_FRONT=1]

span<>: Allows to change an element via array indexing

span<>: Allows to change an element via call indexing

span<>: Allows to change an element via at() [span_FEATURE_MEMBER_AT>0]

span<>: Allows to change an element via data()

span<>: Allows to change the first element via front() [span_FEATURE_MEMBER_BACK_FRONT=1]

span<>: Allows to change the last element via back() [span_FEATURE_MEMBER_BACK_FRONT=1]

span<>: Allows to swap with another span [span_FEATURE_MEMBER_SWAP=1]

span<>: Allows forward iteration

span<>: Allows const forward iteration

span<>: Allows reverse iteration

span<>: Allows const reverse iteration

span<>: Allows to identify if a span is the same as another span [span_FEATURE_SAME=1]

span<>: Allows to compare equal to another span of the same type [span_FEATURE_COMPARISON=1]

span<>: Allows to compare unequal to another span of the same type [span_FEATURE_COMPARISON=1]

span<>: Allows to compare less than another span of the same type [span_FEATURE_COMPARISON=1]

span<>: Allows to compare less than or equal to another span of the same type [span_FEATURE_COMPARISON=1]

span<>: Allows to compare greater than another span of the same type [span_FEATURE_COMPARISON=1]

span<>: Allows to compare greater than or equal to another span of the same type [span_FEATURE_COMPARISON=1]

span<>: Allows to compare to another span of the same type and different cv-ness [span_FEATURE_SAME=0]

span<>: Allows to compare empty spans as equal [span_FEATURE_COMPARISON=1]

span<>: Allows to test for empty span via empty(), empty case

span<>: Allows to test for empty span via empty(), non-empty case

span<>: Allows to obtain the number of elements via size()

span<>: Allows to obtain the number of elements via ssize()

span<>: Allows to obtain the number of bytes via size_bytes()

span<>: Allows to view the elements as read-only bytes

span<>: Allows to view and change the elements as writable bytes

make_span() [span_FEATURE_MAKE_SPAN_TO_STD=99]

make_span(): Allows building from two pointers

make_span(): Allows building from two const pointers

make_span(): Allows building from a non-null pointer and a size

make_span(): Allows building from a non-null const pointer and a size

make_span(): Allows building from a C-array

make_span(): Allows building from a const C-array

make_span(): Allows building from a std::initializer_list<> (C++11)

make_span(): Allows building from a std::initializer_list<> as a constant set of values (C++11)

make_span(): Allows building from a std::array<> (C++11)

make_span(): Allows building from a const std::array<> (C++11)

make_span(): Allows building from a container (std::vector<>)

make_span(): Allows building from a const container (std::vector<>)

make_span(): Allows building from a container (with_container_t, std::vector<>)

make_span(): Allows building from a const container (with_container_t, std::vector<>)

byte_span() [span_FEATURE_BYTE_SPAN=1]

byte_span(): Allows building a span of std::byte from a single object (C++17, byte-lite)

byte_span(): Allows building a span of const std::byte from a single const object (C++17, byte-lite)

first(), last(), subspan() [span_FEATURE_NON_MEMBER_FIRST_LAST_SUB=1]

first(): Allows to create a sub span of the first n elements (span, template parameter)

first(): Allows to create a sub span of the first n elements (span, function parameter)

first(): Allows to create a sub span of the first n elements (compatible container, template parameter)

first(): Allows to create a sub span of the first n elements (compatible container, function parameter)

last(): Allows to create a sub span of the last n elements (span, template parameter)

last(): Allows to create a sub span of the last n elements (span, function parameter)

last(): Allows to create a sub span of the last n elements (compatible container, template parameter)

last(): Allows to create a sub span of the last n elements (compatible container, function parameter)

subspan(): Allows to create a sub span starting at a given offset (span, template parameter)

subspan(): Allows to create a sub span starting at a given offset (span, function parameter)

subspan(): Allows to create a sub span starting at a given offset (compatible container, template parameter)

subspan(): Allows to create a sub span starting at a given offset (compatible container, function parameter)

size(): Allows to obtain the number of elements via size()

ssize(): Allows to obtain the number of elements via ssize()

tuple_size<>: Allows to obtain the number of elements via std::tuple_size<> (C++11)

tuple_element<>: Allows to obtain an element via std::tuple_element<> (C++11)

tuple_element<>: Allows to obtain an element via std::tuple_element_t<> (C++11)

get(spn): Allows to access an element via std::get<>()

tweak header: reads tweak header if supported [tweak]

```