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Boost Library Requirements and Guidelines

Introduction
Requirements
    License requirements
    Portability requirements
    Ownership
Guidelines
    Design and programming
    Directory structure and filenames
    Naming consistency
    Documentation
Rationale
    Exception-specification rationale
    Naming conventions rationale
    Source code fonts rationale
    Tabs rationale
    ECMAScript/JavaScript rationale
    Rationale rationale
    Acknowledgements rationale

Introduction

This page describes requirements and guidelines for the content of a library submitted to Boost.

See the Boost Library Submission Process page for a description of the process involved.

Requirements

To avoid the frustration and wasted time of a proposed library being rejected, it must meets these requirements:

There's no requirement that an author read the mailing list for a time before making a submission. It has been noted, however, that submissions which begin "I just started to read this mailing list ..." seem to fail, often embarrassingly.

License requirements

The preferred way to meet the license requirements is to use the Boost Software License. See license information. If for any reason you do not intend to use the Boost Software License, please discuss the issues on the Boost developers mailing list first.

The license requirements:

Portability requirements

Since there is no absolute way to prove portability, many boost submissions demonstrate practical portability by compiling and executing correctly with two different C++ compilers, often under different operating systems.  Otherwise reviewers may disbelieve that porting is in fact practical.

Ownership

Are you sure you own the library you are thinking of submitting?   "How to Copyright Software" by MJ Salone, Nolo Press, 1990 says:

Doing work on your own time that is very similar to programming you do for your employer on company time can raise nasty legal problems.  In this situation, it's best to get a written release from your employer in advance.

Place a copyright notice in all the important files you submit. Boost won't accept libraries without clear copyright information.

Guidelines

Please use these guidelines as a checklist for preparing the content a library submission.  Not every guideline applies to every library, but a reasonable effort to comply is expected.

Design and Programming

Directory Structure and Filenames

Boost standard sub-directory names

Sub-directory Contents Required
build Library build files such as a Jamfile. If any build files.
doc Documentation (HTML) files. If several doc files.
example Sample program files. If several sample files.
src Source files which must be compiled to build the library.  If any source files.
test Regression or other test programs or scripts. If several test files.

Redirection

The primary directory should always contain a file named index.html (or index.htm). Authors have requested this so that they can publish URL's in the form http://www.boost.org/libs/lib-name with the assurance a documentation reorganization won't invalidate the URL. Boost's internal tools are also simplified by knowing that a library's documentation is always reachable via the simplified URL.

If the documentation is in a doc sub-directory, the primary directory index.html file should just do an automatic redirection to the doc subdirectory:

<html>
<head>
<meta http-equiv="refresh" content="0; URL=doc/index.html">
</head>
<body>
Automatic redirection failed, please go to
<a href="doc/index.html">doc/index.html</a>

</body>
</html>

Naming consistency

As library developers and users have gained experience with Boost, the following consistent naming approach has come to be viewed as very helpful, particularly for larger libraries that need their own header subdirectories and namespaces.

Here is how it works. The library is given a name that describes the contents of the library. Cryptic abbreviations are strongly discouraged. Following the practice of the C++ Standard Library, names are usually singular rather than plural. For example, a library dealing with file systems might chose the name "filesystem", but not "filesystems", "fs" or "nicecode".

When documenting Boost libraries, follow these conventions (see also the following section of this document):

Here are a few examples of how to apply these conventions:

Documentation

Even the simplest library needs some documentation; the amount should be proportional to the need.  The documentation should assume the readers have a basic knowledge of C++, but are not necessarily experts.

The format for documentation should be HTML, and should not require an advanced browser or server-side extensions. Style sheets are acceptable. ECMAScript/JavaScript is not acceptable. The documentation entry point should always be a file named index.html or index.htm; see Redirection.

There is no single right way to do documentation. HTML documentation is often organized quite differently from traditional printed documents. Task-oriented styles differ from reference oriented styles. In the end, it comes down to the question: Is the documentation sufficient for the mythical "average" C++ programmer to use the library successfully?

Appropriate topics for documentation often include:

If you need more help with how to write documentation you can check out the article on Writing Documentation for Boost.

Rationale

Rationale for some of the requirements and guidelines follows.


Exception-specification rationale

Exception specifications [ISO 15.4] are sometimes coded to indicate what exceptions may be thrown, or because the programmer hopes they will improved performance.  But consider the following member from a smart pointer:

    T& operator*() const throw()  { return *ptr; }

This function calls no other functions; it only manipulates fundamental data types like pointers Therefore, no runtime behavior of the exception-specification can ever be invoked.  The function is completely exposed to the compiler; indeed it is declared inline Therefore, a smart compiler can easily deduce that the functions are incapable of throwing exceptions, and make the same optimizations it would have made based on the empty exception-specification. A "dumb" compiler, however, may make all kinds of pessimizations.

For example, some compilers turn off inlining if there is an exception-specification.  Some compilers add try/catch blocks. Such pessimizations can be a performance disaster which makes the code unusable in practical applications.

Although initially appealing, an exception-specification tends to have consequences that require very careful thought to understand. The biggest problem with exception-specifications is that programmers use them as though they have the effect the programmer would like, instead of the effect they actually have.

A non-inline function is the one place a "throws nothing" exception-specification may have some benefit with some compilers.


Naming conventions rationale

The C++ standard committee's Library Working Group discussed this issue in detail, and over a long period of time. The discussion was repeated again in early boost postings. A short summary:


Source code fonts rationale

Dave Abrahams comments: An important purpose (I daresay the primary purpose) of source code is communication: the documentation of intent. This is a doubly important goal for boost, I think. Using a fixed-width font allows us to communicate with more people, in more ways (diagrams are possible) right there in the source. Code written for fixed-width fonts using spaces will read reasonably well when viewed with a variable-width font, and as far as I can tell every editor supporting variable-width fonts also supports fixed width. I don't think the converse is true.


Tabs rationale

Tabs are banned because of the practical problems caused by tabs in multi-developer projects like Boost, rather than any dislike in principle. See mailing list archives. Problems include maintenance of a single source file by programmers using tabs and programmers using spaces, and the difficulty of enforcing a consistent tab policy other than just "no tabs". Discussions concluded that Boost files should either all use tabs, or all use spaces, and thus the decision to stick with spaces.


ECMAScript/JavaScript rationale

Before the 1.29.0 release, two Boost libraries added ECMAScript/JavaScript documentation. Controversy followed (see mailing list archives), and the developers were asked to remove the ECMAScript/JavaScript. Reasons given for banning included:


Rationale rationale

Rationale is defined as "The fundamental reasons for something; basis" by the American Heritage Dictionary.

Beman Dawes comments:  Failure to supply contemporaneous rationale for design decisions is a major defect in many software projects. Lack of accurate rationale causes issues to be revisited endlessly, causes maintenance bugs when a maintainer changes something without realizing it was done a certain way for some purpose, and shortens the useful lifetime of software.

Rationale is fairly easy to provide at the time decisions are made, but very hard to accurately recover even a short time later.


Acknowledgements rationale

As a library matures, it almost always accumulates improvements suggested to the authors by other boost members.  It is a part of the culture of boost.org to acknowledge such contributions, identifying the person making the suggestion.  Major contributions are usually acknowledged in the documentation, while minor fixes are often mentioned in comments within the code itself.


Revised 04 November, 2003

© Copyright Beman Dawes 2003.

Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at www.boost.org/LICENSE_1_0.txt)