| 1 | =head1 NAME |
| 2 | |
| 3 | perlmodstyle - Perl module style guide |
| 4 | |
| 5 | =head1 INTRODUCTION |
| 6 | |
| 7 | This document attempts to describe the Perl Community's "best practice" |
| 8 | for writing Perl modules. It extends the recommendations found in |
| 9 | L<perlstyle> , which should be considered required reading |
| 10 | before reading this document. |
| 11 | |
| 12 | While this document is intended to be useful to all module authors, it is |
| 13 | particularly aimed at authors who wish to publish their modules on CPAN. |
| 14 | |
| 15 | The focus is on elements of style which are visible to the users of a |
| 16 | module, rather than those parts which are only seen by the module's |
| 17 | developers. However, many of the guidelines presented in this document |
| 18 | can be extrapolated and applied successfully to a module's internals. |
| 19 | |
| 20 | This document differs from L<perlnewmod> in that it is a style guide |
| 21 | rather than a tutorial on creating CPAN modules. It provides a |
| 22 | checklist against which modules can be compared to determine whether |
| 23 | they conform to best practice, without necessarily describing in detail |
| 24 | how to achieve this. |
| 25 | |
| 26 | All the advice contained in this document has been gleaned from |
| 27 | extensive conversations with experienced CPAN authors and users. Every |
| 28 | piece of advice given here is the result of previous mistakes. This |
| 29 | information is here to help you avoid the same mistakes and the extra |
| 30 | work that would inevitably be required to fix them. |
| 31 | |
| 32 | The first section of this document provides an itemized checklist; |
| 33 | subsequent sections provide a more detailed discussion of the items on |
| 34 | the list. The final section, "Common Pitfalls", describes some of the |
| 35 | most popular mistakes made by CPAN authors. |
| 36 | |
| 37 | =head1 QUICK CHECKLIST |
| 38 | |
| 39 | For more detail on each item in this checklist, see below. |
| 40 | |
| 41 | =head2 Before you start |
| 42 | |
| 43 | =over 4 |
| 44 | |
| 45 | =item * |
| 46 | |
| 47 | Don't re-invent the wheel |
| 48 | |
| 49 | =item * |
| 50 | |
| 51 | Patch, extend or subclass an existing module where possible |
| 52 | |
| 53 | =item * |
| 54 | |
| 55 | Do one thing and do it well |
| 56 | |
| 57 | =item * |
| 58 | |
| 59 | Choose an appropriate name |
| 60 | |
| 61 | =item * |
| 62 | |
| 63 | Get feedback before publishing |
| 64 | |
| 65 | =back |
| 66 | |
| 67 | =head2 The API |
| 68 | |
| 69 | =over 4 |
| 70 | |
| 71 | =item * |
| 72 | |
| 73 | API should be understandable by the average programmer |
| 74 | |
| 75 | =item * |
| 76 | |
| 77 | Simple methods for simple tasks |
| 78 | |
| 79 | =item * |
| 80 | |
| 81 | Separate functionality from output |
| 82 | |
| 83 | =item * |
| 84 | |
| 85 | Consistent naming of subroutines or methods |
| 86 | |
| 87 | =item * |
| 88 | |
| 89 | Use named parameters (a hash or hashref) when there are more than two |
| 90 | parameters |
| 91 | |
| 92 | =back |
| 93 | |
| 94 | =head2 Stability |
| 95 | |
| 96 | =over 4 |
| 97 | |
| 98 | =item * |
| 99 | |
| 100 | Ensure your module works under C<use strict> and C<-w> |
| 101 | |
| 102 | =item * |
| 103 | |
| 104 | Stable modules should maintain backwards compatibility |
| 105 | |
| 106 | =back |
| 107 | |
| 108 | =head2 Documentation |
| 109 | |
| 110 | =over 4 |
| 111 | |
| 112 | =item * |
| 113 | |
| 114 | Write documentation in POD |
| 115 | |
| 116 | =item * |
| 117 | |
| 118 | Document purpose, scope and target applications |
| 119 | |
| 120 | =item * |
| 121 | |
| 122 | Document each publically accessible method or subroutine, including params and return values |
| 123 | |
| 124 | =item * |
| 125 | |
| 126 | Give examples of use in your documentation |
| 127 | |
| 128 | =item * |
| 129 | |
| 130 | Provide a README file and perhaps also release notes, changelog, etc |
| 131 | |
| 132 | =item * |
| 133 | |
| 134 | Provide links to further information (URL, email) |
| 135 | |
| 136 | =back |
| 137 | |
| 138 | =head2 Release considerations |
| 139 | |
| 140 | =over 4 |
| 141 | |
| 142 | =item * |
| 143 | |
| 144 | Specify pre-requisites in Makefile.PL or Build.PL |
| 145 | |
| 146 | =item * |
| 147 | |
| 148 | Specify Perl version requirements with C<use> |
| 149 | |
| 150 | =item * |
| 151 | |
| 152 | Include tests with your module |
| 153 | |
| 154 | =item * |
| 155 | |
| 156 | Choose a sensible and consistent version numbering scheme (X.YY is the common Perl module numbering scheme) |
| 157 | |
| 158 | =item * |
| 159 | |
| 160 | Increment the version number for every change, no matter how small |
| 161 | |
| 162 | =item * |
| 163 | |
| 164 | Package the module using "make dist" |
| 165 | |
| 166 | =item * |
| 167 | |
| 168 | Choose an appropriate license (GPL/Artistic is a good default) |
| 169 | |
| 170 | =back |
| 171 | |
| 172 | =head1 BEFORE YOU START WRITING A MODULE |
| 173 | |
| 174 | Try not to launch headlong into developing your module without spending |
| 175 | some time thinking first. A little forethought may save you a vast |
| 176 | amount of effort later on. |
| 177 | |
| 178 | =head2 Has it been done before? |
| 179 | |
| 180 | You may not even need to write the module. Check whether it's already |
| 181 | been done in Perl, and avoid re-inventing the wheel unless you have a |
| 182 | good reason. |
| 183 | |
| 184 | Good places to look for pre-existing modules include |
| 185 | L<http://search.cpan.org/> and L<https://metacpan.org> |
| 186 | and asking on C<module-authors@perl.org> |
| 187 | (L<http://lists.perl.org/list/module-authors.html>). |
| 188 | |
| 189 | If an existing module B<almost> does what you want, consider writing a |
| 190 | patch, writing a subclass, or otherwise extending the existing module |
| 191 | rather than rewriting it. |
| 192 | |
| 193 | =head2 Do one thing and do it well |
| 194 | |
| 195 | At the risk of stating the obvious, modules are intended to be modular. |
| 196 | A Perl developer should be able to use modules to put together the |
| 197 | building blocks of their application. However, it's important that the |
| 198 | blocks are the right shape, and that the developer shouldn't have to use |
| 199 | a big block when all they need is a small one. |
| 200 | |
| 201 | Your module should have a clearly defined scope which is no longer than |
| 202 | a single sentence. Can your module be broken down into a family of |
| 203 | related modules? |
| 204 | |
| 205 | Bad example: |
| 206 | |
| 207 | "FooBar.pm provides an implementation of the FOO protocol and the |
| 208 | related BAR standard." |
| 209 | |
| 210 | Good example: |
| 211 | |
| 212 | "Foo.pm provides an implementation of the FOO protocol. Bar.pm |
| 213 | implements the related BAR protocol." |
| 214 | |
| 215 | This means that if a developer only needs a module for the BAR standard, |
| 216 | they should not be forced to install libraries for FOO as well. |
| 217 | |
| 218 | =head2 What's in a name? |
| 219 | |
| 220 | Make sure you choose an appropriate name for your module early on. This |
| 221 | will help people find and remember your module, and make programming |
| 222 | with your module more intuitive. |
| 223 | |
| 224 | When naming your module, consider the following: |
| 225 | |
| 226 | =over 4 |
| 227 | |
| 228 | =item * |
| 229 | |
| 230 | Be descriptive (i.e. accurately describes the purpose of the module). |
| 231 | |
| 232 | =item * |
| 233 | |
| 234 | Be consistent with existing modules. |
| 235 | |
| 236 | =item * |
| 237 | |
| 238 | Reflect the functionality of the module, not the implementation. |
| 239 | |
| 240 | =item * |
| 241 | |
| 242 | Avoid starting a new top-level hierarchy, especially if a suitable |
| 243 | hierarchy already exists under which you could place your module. |
| 244 | |
| 245 | =back |
| 246 | |
| 247 | =head2 Get feedback before publishing |
| 248 | |
| 249 | If you have never uploaded a module to CPAN before (and even if you have), |
| 250 | you are strongly encouraged to get feedback on L<PrePAN|http://prepan.org>. |
| 251 | PrePAN is a site dedicated to discussing ideas for CPAN modules with other |
| 252 | Perl developers and is a great resource for new (and experienced) Perl |
| 253 | developers. |
| 254 | |
| 255 | You should also try to get feedback from people who are already familiar |
| 256 | with the module's application domain and the CPAN naming system. Authors |
| 257 | of similar modules, or modules with similar names, may be a good place to |
| 258 | start, as are community sites like L<Perl Monks|http://www.perlmonks.org>. |
| 259 | |
| 260 | =head1 DESIGNING AND WRITING YOUR MODULE |
| 261 | |
| 262 | Considerations for module design and coding: |
| 263 | |
| 264 | =head2 To OO or not to OO? |
| 265 | |
| 266 | Your module may be object oriented (OO) or not, or it may have both kinds |
| 267 | of interfaces available. There are pros and cons of each technique, which |
| 268 | should be considered when you design your API. |
| 269 | |
| 270 | In I<Perl Best Practices> (copyright 2004, Published by O'Reilly Media, Inc.), |
| 271 | Damian Conway provides a list of criteria to use when deciding if OO is the |
| 272 | right fit for your problem: |
| 273 | |
| 274 | =over 4 |
| 275 | |
| 276 | =item * |
| 277 | |
| 278 | The system being designed is large, or is likely to become large. |
| 279 | |
| 280 | =item * |
| 281 | |
| 282 | The data can be aggregated into obvious structures, especially if |
| 283 | there's a large amount of data in each aggregate. |
| 284 | |
| 285 | =item * |
| 286 | |
| 287 | The various types of data aggregate form a natural hierarchy that |
| 288 | facilitates the use of inheritance and polymorphism. |
| 289 | |
| 290 | =item * |
| 291 | |
| 292 | You have a piece of data on which many different operations are |
| 293 | applied. |
| 294 | |
| 295 | =item * |
| 296 | |
| 297 | You need to perform the same general operations on related types of |
| 298 | data, but with slight variations depending on the specific type of data |
| 299 | the operations are applied to. |
| 300 | |
| 301 | =item * |
| 302 | |
| 303 | It's likely you'll have to add new data types later. |
| 304 | |
| 305 | =item * |
| 306 | |
| 307 | The typical interactions between pieces of data are best represented by |
| 308 | operators. |
| 309 | |
| 310 | =item * |
| 311 | |
| 312 | The implementation of individual components of the system is likely to |
| 313 | change over time. |
| 314 | |
| 315 | =item * |
| 316 | |
| 317 | The system design is already object-oriented. |
| 318 | |
| 319 | =item * |
| 320 | |
| 321 | Large numbers of other programmers will be using your code modules. |
| 322 | |
| 323 | =back |
| 324 | |
| 325 | Think carefully about whether OO is appropriate for your module. |
| 326 | Gratuitous object orientation results in complex APIs which are |
| 327 | difficult for the average module user to understand or use. |
| 328 | |
| 329 | =head2 Designing your API |
| 330 | |
| 331 | Your interfaces should be understandable by an average Perl programmer. |
| 332 | The following guidelines may help you judge whether your API is |
| 333 | sufficiently straightforward: |
| 334 | |
| 335 | =over 4 |
| 336 | |
| 337 | =item Write simple routines to do simple things. |
| 338 | |
| 339 | It's better to have numerous simple routines than a few monolithic ones. |
| 340 | If your routine changes its behaviour significantly based on its |
| 341 | arguments, it's a sign that you should have two (or more) separate |
| 342 | routines. |
| 343 | |
| 344 | =item Separate functionality from output. |
| 345 | |
| 346 | Return your results in the most generic form possible and allow the user |
| 347 | to choose how to use them. The most generic form possible is usually a |
| 348 | Perl data structure which can then be used to generate a text report, |
| 349 | HTML, XML, a database query, or whatever else your users require. |
| 350 | |
| 351 | If your routine iterates through some kind of list (such as a list of |
| 352 | files, or records in a database) you may consider providing a callback |
| 353 | so that users can manipulate each element of the list in turn. |
| 354 | File::Find provides an example of this with its |
| 355 | C<find(\&wanted, $dir)> syntax. |
| 356 | |
| 357 | =item Provide sensible shortcuts and defaults. |
| 358 | |
| 359 | Don't require every module user to jump through the same hoops to achieve a |
| 360 | simple result. You can always include optional parameters or routines for |
| 361 | more complex or non-standard behaviour. If most of your users have to |
| 362 | type a few almost identical lines of code when they start using your |
| 363 | module, it's a sign that you should have made that behaviour a default. |
| 364 | Another good indicator that you should use defaults is if most of your |
| 365 | users call your routines with the same arguments. |
| 366 | |
| 367 | =item Naming conventions |
| 368 | |
| 369 | Your naming should be consistent. For instance, it's better to have: |
| 370 | |
| 371 | display_day(); |
| 372 | display_week(); |
| 373 | display_year(); |
| 374 | |
| 375 | than |
| 376 | |
| 377 | display_day(); |
| 378 | week_display(); |
| 379 | show_year(); |
| 380 | |
| 381 | This applies equally to method names, parameter names, and anything else |
| 382 | which is visible to the user (and most things that aren't!) |
| 383 | |
| 384 | =item Parameter passing |
| 385 | |
| 386 | Use named parameters. It's easier to use a hash like this: |
| 387 | |
| 388 | $obj->do_something( |
| 389 | name => "wibble", |
| 390 | type => "text", |
| 391 | size => 1024, |
| 392 | ); |
| 393 | |
| 394 | ... than to have a long list of unnamed parameters like this: |
| 395 | |
| 396 | $obj->do_something("wibble", "text", 1024); |
| 397 | |
| 398 | While the list of arguments might work fine for one, two or even three |
| 399 | arguments, any more arguments become hard for the module user to |
| 400 | remember, and hard for the module author to manage. If you want to add |
| 401 | a new parameter you will have to add it to the end of the list for |
| 402 | backward compatibility, and this will probably make your list order |
| 403 | unintuitive. Also, if many elements may be undefined you may see the |
| 404 | following unattractive method calls: |
| 405 | |
| 406 | $obj->do_something(undef, undef, undef, undef, undef, 1024); |
| 407 | |
| 408 | Provide sensible defaults for parameters which have them. Don't make |
| 409 | your users specify parameters which will almost always be the same. |
| 410 | |
| 411 | The issue of whether to pass the arguments in a hash or a hashref is |
| 412 | largely a matter of personal style. |
| 413 | |
| 414 | The use of hash keys starting with a hyphen (C<-name>) or entirely in |
| 415 | upper case (C<NAME>) is a relic of older versions of Perl in which |
| 416 | ordinary lower case strings were not handled correctly by the C<=E<gt>> |
| 417 | operator. While some modules retain uppercase or hyphenated argument |
| 418 | keys for historical reasons or as a matter of personal style, most new |
| 419 | modules should use simple lower case keys. Whatever you choose, be |
| 420 | consistent! |
| 421 | |
| 422 | =back |
| 423 | |
| 424 | =head2 Strictness and warnings |
| 425 | |
| 426 | Your module should run successfully under the strict pragma and should |
| 427 | run without generating any warnings. Your module should also handle |
| 428 | taint-checking where appropriate, though this can cause difficulties in |
| 429 | many cases. |
| 430 | |
| 431 | =head2 Backwards compatibility |
| 432 | |
| 433 | Modules which are "stable" should not break backwards compatibility |
| 434 | without at least a long transition phase and a major change in version |
| 435 | number. |
| 436 | |
| 437 | =head2 Error handling and messages |
| 438 | |
| 439 | When your module encounters an error it should do one or more of: |
| 440 | |
| 441 | =over 4 |
| 442 | |
| 443 | =item * |
| 444 | |
| 445 | Return an undefined value. |
| 446 | |
| 447 | =item * |
| 448 | |
| 449 | set C<$Module::errstr> or similar (C<errstr> is a common name used by |
| 450 | DBI and other popular modules; if you choose something else, be sure to |
| 451 | document it clearly). |
| 452 | |
| 453 | =item * |
| 454 | |
| 455 | C<warn()> or C<carp()> a message to STDERR. |
| 456 | |
| 457 | =item * |
| 458 | |
| 459 | C<croak()> only when your module absolutely cannot figure out what to |
| 460 | do. (C<croak()> is a better version of C<die()> for use within |
| 461 | modules, which reports its errors from the perspective of the caller. |
| 462 | See L<Carp> for details of C<croak()>, C<carp()> and other useful |
| 463 | routines.) |
| 464 | |
| 465 | =item * |
| 466 | |
| 467 | As an alternative to the above, you may prefer to throw exceptions using |
| 468 | the Error module. |
| 469 | |
| 470 | =back |
| 471 | |
| 472 | Configurable error handling can be very useful to your users. Consider |
| 473 | offering a choice of levels for warning and debug messages, an option to |
| 474 | send messages to a separate file, a way to specify an error-handling |
| 475 | routine, or other such features. Be sure to default all these options |
| 476 | to the commonest use. |
| 477 | |
| 478 | =head1 DOCUMENTING YOUR MODULE |
| 479 | |
| 480 | =head2 POD |
| 481 | |
| 482 | Your module should include documentation aimed at Perl developers. |
| 483 | You should use Perl's "plain old documentation" (POD) for your general |
| 484 | technical documentation, though you may wish to write additional |
| 485 | documentation (white papers, tutorials, etc) in some other format. |
| 486 | You need to cover the following subjects: |
| 487 | |
| 488 | =over 4 |
| 489 | |
| 490 | =item * |
| 491 | |
| 492 | A synopsis of the common uses of the module |
| 493 | |
| 494 | =item * |
| 495 | |
| 496 | The purpose, scope and target applications of your module |
| 497 | |
| 498 | =item * |
| 499 | |
| 500 | Use of each publically accessible method or subroutine, including |
| 501 | parameters and return values |
| 502 | |
| 503 | =item * |
| 504 | |
| 505 | Examples of use |
| 506 | |
| 507 | =item * |
| 508 | |
| 509 | Sources of further information |
| 510 | |
| 511 | =item * |
| 512 | |
| 513 | A contact email address for the author/maintainer |
| 514 | |
| 515 | =back |
| 516 | |
| 517 | The level of detail in Perl module documentation generally goes from |
| 518 | less detailed to more detailed. Your SYNOPSIS section should contain a |
| 519 | minimal example of use (perhaps as little as one line of code; skip the |
| 520 | unusual use cases or anything not needed by most users); the |
| 521 | DESCRIPTION should describe your module in broad terms, generally in |
| 522 | just a few paragraphs; more detail of the module's routines or methods, |
| 523 | lengthy code examples, or other in-depth material should be given in |
| 524 | subsequent sections. |
| 525 | |
| 526 | Ideally, someone who's slightly familiar with your module should be able |
| 527 | to refresh their memory without hitting "page down". As your reader |
| 528 | continues through the document, they should receive a progressively |
| 529 | greater amount of knowledge. |
| 530 | |
| 531 | The recommended order of sections in Perl module documentation is: |
| 532 | |
| 533 | =over 4 |
| 534 | |
| 535 | =item * |
| 536 | |
| 537 | NAME |
| 538 | |
| 539 | =item * |
| 540 | |
| 541 | SYNOPSIS |
| 542 | |
| 543 | =item * |
| 544 | |
| 545 | DESCRIPTION |
| 546 | |
| 547 | =item * |
| 548 | |
| 549 | One or more sections or subsections giving greater detail of available |
| 550 | methods and routines and any other relevant information. |
| 551 | |
| 552 | =item * |
| 553 | |
| 554 | BUGS/CAVEATS/etc |
| 555 | |
| 556 | =item * |
| 557 | |
| 558 | AUTHOR |
| 559 | |
| 560 | =item * |
| 561 | |
| 562 | SEE ALSO |
| 563 | |
| 564 | =item * |
| 565 | |
| 566 | COPYRIGHT and LICENSE |
| 567 | |
| 568 | =back |
| 569 | |
| 570 | Keep your documentation near the code it documents ("inline" |
| 571 | documentation). Include POD for a given method right above that |
| 572 | method's subroutine. This makes it easier to keep the documentation up |
| 573 | to date, and avoids having to document each piece of code twice (once in |
| 574 | POD and once in comments). |
| 575 | |
| 576 | =head2 README, INSTALL, release notes, changelogs |
| 577 | |
| 578 | Your module should also include a README file describing the module and |
| 579 | giving pointers to further information (website, author email). |
| 580 | |
| 581 | An INSTALL file should be included, and should contain simple installation |
| 582 | instructions. When using ExtUtils::MakeMaker this will usually be: |
| 583 | |
| 584 | =over 4 |
| 585 | |
| 586 | =item perl Makefile.PL |
| 587 | |
| 588 | =item make |
| 589 | |
| 590 | =item make test |
| 591 | |
| 592 | =item make install |
| 593 | |
| 594 | =back |
| 595 | |
| 596 | When using Module::Build, this will usually be: |
| 597 | |
| 598 | =over 4 |
| 599 | |
| 600 | =item perl Build.PL |
| 601 | |
| 602 | =item perl Build |
| 603 | |
| 604 | =item perl Build test |
| 605 | |
| 606 | =item perl Build install |
| 607 | |
| 608 | =back |
| 609 | |
| 610 | Release notes or changelogs should be produced for each release of your |
| 611 | software describing user-visible changes to your module, in terms |
| 612 | relevant to the user. |
| 613 | |
| 614 | Unless you have good reasons for using some other format |
| 615 | (for example, a format used within your company), |
| 616 | the convention is to name your changelog file C<Changes>, |
| 617 | and to follow the simple format described in L<CPAN::Changes::Spec>. |
| 618 | |
| 619 | =head1 RELEASE CONSIDERATIONS |
| 620 | |
| 621 | =head2 Version numbering |
| 622 | |
| 623 | Version numbers should indicate at least major and minor releases, and |
| 624 | possibly sub-minor releases. A major release is one in which most of |
| 625 | the functionality has changed, or in which major new functionality is |
| 626 | added. A minor release is one in which a small amount of functionality |
| 627 | has been added or changed. Sub-minor version numbers are usually used |
| 628 | for changes which do not affect functionality, such as documentation |
| 629 | patches. |
| 630 | |
| 631 | The most common CPAN version numbering scheme looks like this: |
| 632 | |
| 633 | 1.00, 1.10, 1.11, 1.20, 1.30, 1.31, 1.32 |
| 634 | |
| 635 | A correct CPAN version number is a floating point number with at least |
| 636 | 2 digits after the decimal. You can test whether it conforms to CPAN by |
| 637 | using |
| 638 | |
| 639 | perl -MExtUtils::MakeMaker -le 'print MM->parse_version(shift)' \ |
| 640 | 'Foo.pm' |
| 641 | |
| 642 | If you want to release a 'beta' or 'alpha' version of a module but |
| 643 | don't want CPAN.pm to list it as most recent use an '_' after the |
| 644 | regular version number followed by at least 2 digits, eg. 1.20_01. If |
| 645 | you do this, the following idiom is recommended: |
| 646 | |
| 647 | our $VERSION = "1.12_01"; # so CPAN distribution will have |
| 648 | # right filename |
| 649 | our $XS_VERSION = $VERSION; # only needed if you have XS code |
| 650 | $VERSION = eval $VERSION; # so "use Module 0.002" won't warn on |
| 651 | # underscore |
| 652 | |
| 653 | With that trick MakeMaker will only read the first line and thus read |
| 654 | the underscore, while the perl interpreter will evaluate the $VERSION |
| 655 | and convert the string into a number. Later operations that treat |
| 656 | $VERSION as a number will then be able to do so without provoking a |
| 657 | warning about $VERSION not being a number. |
| 658 | |
| 659 | Never release anything (even a one-word documentation patch) without |
| 660 | incrementing the number. Even a one-word documentation patch should |
| 661 | result in a change in version at the sub-minor level. |
| 662 | |
| 663 | Once picked, it is important to stick to your version scheme, without |
| 664 | reducing the number of digits. This is because "downstream" packagers, |
| 665 | such as the FreeBSD ports system, interpret the version numbers in |
| 666 | various ways. If you change the number of digits in your version scheme, |
| 667 | you can confuse these systems so they get the versions of your module |
| 668 | out of order, which is obviously bad. |
| 669 | |
| 670 | =head2 Pre-requisites |
| 671 | |
| 672 | Module authors should carefully consider whether to rely on other |
| 673 | modules, and which modules to rely on. |
| 674 | |
| 675 | Most importantly, choose modules which are as stable as possible. In |
| 676 | order of preference: |
| 677 | |
| 678 | =over 4 |
| 679 | |
| 680 | =item * |
| 681 | |
| 682 | Core Perl modules |
| 683 | |
| 684 | =item * |
| 685 | |
| 686 | Stable CPAN modules |
| 687 | |
| 688 | =item * |
| 689 | |
| 690 | Unstable CPAN modules |
| 691 | |
| 692 | =item * |
| 693 | |
| 694 | Modules not available from CPAN |
| 695 | |
| 696 | =back |
| 697 | |
| 698 | Specify version requirements for other Perl modules in the |
| 699 | pre-requisites in your Makefile.PL or Build.PL. |
| 700 | |
| 701 | Be sure to specify Perl version requirements both in Makefile.PL or |
| 702 | Build.PL and with C<require 5.6.1> or similar. See the section on |
| 703 | C<use VERSION> of L<perlfunc/require> for details. |
| 704 | |
| 705 | =head2 Testing |
| 706 | |
| 707 | All modules should be tested before distribution (using "make disttest"), |
| 708 | and the tests should also be available to people installing the modules |
| 709 | (using "make test"). |
| 710 | For Module::Build you would use the C<make test> equivalent C<perl Build test>. |
| 711 | |
| 712 | The importance of these tests is proportional to the alleged stability of a |
| 713 | module. A module which purports to be |
| 714 | stable or which hopes to achieve wide |
| 715 | use should adhere to as strict a testing regime as possible. |
| 716 | |
| 717 | Useful modules to help you write tests (with minimum impact on your |
| 718 | development process or your time) include Test::Simple, Carp::Assert |
| 719 | and Test::Inline. |
| 720 | For more sophisticated test suites there are Test::More and Test::MockObject. |
| 721 | |
| 722 | =head2 Packaging |
| 723 | |
| 724 | Modules should be packaged using one of the standard packaging tools. |
| 725 | Currently you have the choice between ExtUtils::MakeMaker and the |
| 726 | more platform independent Module::Build, allowing modules to be installed in a |
| 727 | consistent manner. |
| 728 | When using ExtUtils::MakeMaker, you can use "make dist" to create your |
| 729 | package. Tools exist to help you to build your module in a |
| 730 | MakeMaker-friendly style. These include ExtUtils::ModuleMaker and h2xs. |
| 731 | See also L<perlnewmod>. |
| 732 | |
| 733 | =head2 Licensing |
| 734 | |
| 735 | Make sure that your module has a license, and that the full text of it |
| 736 | is included in the distribution (unless it's a common one and the terms |
| 737 | of the license don't require you to include it). |
| 738 | |
| 739 | If you don't know what license to use, dual licensing under the GPL |
| 740 | and Artistic licenses (the same as Perl itself) is a good idea. |
| 741 | See L<perlgpl> and L<perlartistic>. |
| 742 | |
| 743 | =head1 COMMON PITFALLS |
| 744 | |
| 745 | =head2 Reinventing the wheel |
| 746 | |
| 747 | There are certain application spaces which are already very, very well |
| 748 | served by CPAN. One example is templating systems, another is date and |
| 749 | time modules, and there are many more. While it is a rite of passage to |
| 750 | write your own version of these things, please consider carefully |
| 751 | whether the Perl world really needs you to publish it. |
| 752 | |
| 753 | =head2 Trying to do too much |
| 754 | |
| 755 | Your module will be part of a developer's toolkit. It will not, in |
| 756 | itself, form the B<entire> toolkit. It's tempting to add extra features |
| 757 | until your code is a monolithic system rather than a set of modular |
| 758 | building blocks. |
| 759 | |
| 760 | =head2 Inappropriate documentation |
| 761 | |
| 762 | Don't fall into the trap of writing for the wrong audience. Your |
| 763 | primary audience is a reasonably experienced developer with at least |
| 764 | a moderate understanding of your module's application domain, who's just |
| 765 | downloaded your module and wants to start using it as quickly as possible. |
| 766 | |
| 767 | Tutorials, end-user documentation, research papers, FAQs etc are not |
| 768 | appropriate in a module's main documentation. If you really want to |
| 769 | write these, include them as sub-documents such as C<My::Module::Tutorial> or |
| 770 | C<My::Module::FAQ> and provide a link in the SEE ALSO section of the |
| 771 | main documentation. |
| 772 | |
| 773 | =head1 SEE ALSO |
| 774 | |
| 775 | =over 4 |
| 776 | |
| 777 | =item L<perlstyle> |
| 778 | |
| 779 | General Perl style guide |
| 780 | |
| 781 | =item L<perlnewmod> |
| 782 | |
| 783 | How to create a new module |
| 784 | |
| 785 | =item L<perlpod> |
| 786 | |
| 787 | POD documentation |
| 788 | |
| 789 | =item L<podchecker> |
| 790 | |
| 791 | Verifies your POD's correctness |
| 792 | |
| 793 | =item Packaging Tools |
| 794 | |
| 795 | L<ExtUtils::MakeMaker>, L<Module::Build> |
| 796 | |
| 797 | =item Testing tools |
| 798 | |
| 799 | L<Test::Simple>, L<Test::Inline>, L<Carp::Assert>, L<Test::More>, L<Test::MockObject> |
| 800 | |
| 801 | =item http://pause.perl.org/ |
| 802 | |
| 803 | Perl Authors Upload Server. Contains links to information for module |
| 804 | authors. |
| 805 | |
| 806 | =item Any good book on software engineering |
| 807 | |
| 808 | =back |
| 809 | |
| 810 | =head1 AUTHOR |
| 811 | |
| 812 | Kirrily "Skud" Robert <skud@cpan.org> |
| 813 | |