Perl 5.16 and Beyond

Friday, July 29, 11

Jesse Vincent

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Pumpking

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Former Perl 6Project Manager

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What's a Pumpking?

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BDFL

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BDFL

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BDFL

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I make decisions

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I’m a manager

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I don’t do “real work”

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So, who makes Perl?

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Many awesome people

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I just stand around looking pretty...

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...while other people do awesome stuff

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Is your name in Perl’s AUTHORS file?

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Are you aCPAN author?

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You rock

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You make Perl

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The Release Process

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Releases in the last 12-or-so months:

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5.12.2

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5.12.3

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5.12.4

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5.13.2

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5.13.3

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5.13.4

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5.13.5

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5.13.6

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5.13.7

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5.13.8

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5.13.9

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5.13.10

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5.13.11

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5.14.0

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5.14.1

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5.15.0

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5.15.1

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Perl 5.14.1 is the current release

of Perl 5

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It came out 6ish weeks ago

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As did Perl 5.12.4

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As did Perl 5.15.0

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It used to take us 3 weeks to prepare

a release

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And we made the Pumpking do it

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Now it takesless than a day

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The 43 step process is documented

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Releases are still a chore if you do them

every month

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Now we have rotating release engineers

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Most of them arenew committers

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Nice side effect:release engineers

need commit bits

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Since the move to git, we’ve nearly doubled

our committer list

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The world hasn’t ended

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Some of those release engineers have become

prolific contributors

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I just make decisions

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I try to get them right

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Sometimes they’re wrong

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I have a littlebit of cover

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Rule 1

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Larry is always right

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Rule 2

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Larry is allowed to change his mind

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I’m not Larry

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I’m nowhere near as clever

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My shirts are nowhere near as loud

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At YAPC::NA, Larry said that the time of

hero-pumpkings is over

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D

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Dictator

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Delegator

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Documenter

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Thankfully, Larry’s rules set me up to succeed

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Rule 1 definitely doesn’t apply tothe Perl 5 runtime

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However

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The core needs more support for Rule 2

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I haven’t heard thisin a while:

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Perl is Dead!

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What I’ve beenhearing lately:

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Where are we going?

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It’s changing too fast. Can you slow down?

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You made regexes crazier?$#@!?

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smartmatch isn’t named correctly...

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...can we rename it to psychoticmatch?

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The future

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I’ve been accused of lacking a vision for Perl

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What I lack is aflame-proof suit.

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If I’d talked about my vision 2 years ago...

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You would havelaughed at me

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...now that we can do do releases...

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A Vision

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New versions of Perl shouldn’t break your

existing software

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Old syntax and semantics can’t stop Perl 5 from evolving

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We need to be able to make mistakes

as we rebuild Perl 5

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We willmake mistakes

as we rebuild Perl 5

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*coughsmartmatchcough*

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We have made mistakes

as we’ve rebuilt Perl

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We need to be able to recover from mistakes

as we rebuild Perl

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The runtime footprint is too big and must be

slimmed down

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Perl should havesane defaults

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It should be possible to build more of Perl

in Perl

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Perl should run everywhere

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Not just on every kind of hardware

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or every OS

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Every VM

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Every Browser

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Every Phone

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How do we get there?

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New versions of Perl shouldn’t break

existing software

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Old syntax and semantics must not stop Perl 5

from evolving

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When your code runs, you have no idea

what semantics it’ll see

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You need to jump through defensive

hoops.

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Lots of defensive hoops

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use v5.14;

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“Can I have a Perl that’s 5.14 or newer?”

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“Anything newer than 5.14.0 would be great!”

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“Ok. I’m 5.30. Have fun!”

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That’s not useful

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It needs to change

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Declare the version of Perl 5 you expect

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use v5.16;

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“I want a Perl that works like 5.16”

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The runtime should honor that request

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Perl should give you semantics as close as possible to what you

request

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New features should not work under ‘use v5.$older;’

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It’s critical that we be able to evolve

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We need anescape hatch

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We don’t have one

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We needRule 2

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Changes to syntax or semantics break

existing code

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Why?

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They conflict with existing syntax

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They change the meaning of existing

semantics

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They conflict with things users do

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What do we do?

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If you declare an old version, you get old

syntax and semantics

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...at least to thebest of our abilities

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Perfection isn’t possible

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We can get far closer than we do now

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Breaking existing code should be a last resort

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We will break backward compatibility in limited circumstances

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Some craziness can’t be fixed in an “optional”

or lexical way

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This is going to behard work

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A lot of hard work

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It’s not impossible

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I have proof

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Deprecation

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Our current deprecation cycle

is 1 year

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“It warns in 5.16.0”

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“It’s gone in 5.18.0”

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That’s turning out to be too short

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Very few operating systems release that

frequently

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“Declare by default” means we can make

some changes sooner

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If it still works in old code, we can change it

with no deprecation cycle

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Some old misfeatures need to come out lest they block significant

improvements

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If we can’t emulate the old feature for old

code, we need a longer deprecation cycle

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“It dies in code that declares ‘use v5.16’”

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“It warns in older code on 5.16.0”

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“It still warns in old code on 5.18.0”

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“It’s gone in 5.20.0”

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Old Modules

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We haven’t just been deprecating and yanking

broken old features

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We’ve been doing the same to old modules

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They all end upon CPAN

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This has started to hurt users who wrote code

with “no non-core deps”

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We need to make it easier to ship two flavors of Perl 5

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Hotel California

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aka Traditional Perl

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The Times, They Are A-Changin’

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aka Bootstrappable Perl

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There’s work going on to make this easier

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Cleaning upthe language

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The runtime footprint is too big and must be

slimmed down

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One of the points of doing this is to

clean up the core

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How does this clean up the core?

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Perl is a big language

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There are bigger languages

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It's harder to managea big language

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It’s harder to learna big language

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It’s harder to fix bugs in a big language

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We’re ok, but not amazing at core

language dev

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As a community, we’re awesome at modules

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How do we make Perl a smaller language?

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It’s possible to load modules that inject

new builtins

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It’s possible to load modules that inject

old builtins

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Time to start...

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...refactoring

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Lots of stuff in perl isn't necessarily part of Perl 5 the Language

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This stuff is part of Perl 5 the chainsaw

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I like our chainsaw

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I’m not talking about deprecating this stuff

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...just aboutdecoupling it

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SysV IPC functions

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Socket IO functions

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Unix user & group information functions

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Unix network information functions

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Process and process group functions

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Formats

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smartmatch

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...and probably a bunch of other stuff

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That bit about “forcing a version declaration”

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If you don’t, you’ll get whatever was in 5.14.

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The implementation of SysV might be a module

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As a developer writing code in Perl 5,

you won’t need to care

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..and shouldn’tbe able to tell

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In the future we might fix a bug or two in the

modularized code

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You could take the update without having to upgrade all of Perl 5

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Someday we might remove things from the

default runtime

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Every feature we externalize reclaims precious memory

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Every feature we externalize reclaims

precious sanity

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That just means you’ll need to declare you

want an older feature

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...but only if you ask for v5.16

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...but only if you ask for v5.18

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...but only if you ask for v5.20

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Existing codewon’t break

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There are many, many unanswered questions

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But it’s doable

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I have proof!

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Case study: Smartmatch

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After YAPC::NA rjbs (and others) raised the

issue of smartmatch

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Perl has a history of theft from other

languages

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Perl has a history of borrowing from other

languages

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We stole smartmatchfrom Perl 6

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It’s very clever

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It’s nearlyimpossibleto explain

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It’s nearly impossible

to understand

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RJBS (the previous speaker) proposed a

saner, much less clever, smart match

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I don’t want to break existing code that uses

smartmatch

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Jesse Luehrs (DOY) was sitting in the back

of my YAPC talk

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He...

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...threw himselfat the problem

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He extracted smartmatch intoan XS module

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He reimplemented it entirely in pure perl

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It’s slower, but it’s understandable and

hackable

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He implemented Ricardo’s saner smart match as an alternative

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I’m hoping that 5.16 ships DOY’s smartmatch

implementations

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'use v5.16;' should load the new one in your

scope

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'use v5.14;' should load the old one in your

scope

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no “use v5.x;” line should load the old one

in your scope.

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We need a module hierarchy for such

things in core

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The Test Suite

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(Keeping us honest)

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We have anamazingtest suite

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Over time, we need to tease apart (at least)

3 kinds of tests

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Language tests

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Bug-fix tests

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Implementation tests

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To hold us to the compatibility promises we make, we need a

new test harness

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“Run the test suites we shipped with previous

releases...”

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...all of em

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We've been moving pretty fast

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We’ve done some things I...

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...wouldn’t do again

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I’m going to be a lot more skeptical about

new features

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...at least ones that don’t make it easier to

have fewer features

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We should have sane defaults

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There’s lots of crazyin Perl 5

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Syntactic Crazy

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Semantic Crazy

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Internal Crazy

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Module Crazy

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It may be time to consider doing away with some of that

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But ONLY if you declare “use v5.16”

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But ONLY if you declare “use v5.18”

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But ONLY if you declare “use v5.20”

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We’ve started down this road

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“use v5.12” includes “use strict;”

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Where do we go next?

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warnings on by default

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autodie-esque defaults

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autodie does good for your code

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using deep, scary evil

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I will not show you the evil

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Ask Paul Fenwick

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The guy with the accent

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In the hat

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We should throw exceptions rather than just return on failure

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I don’t want us to bikeshed an exception

hierarchy

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Heck, I’d be happy if we started with dying with

well-defined strings

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(I’d love an exception hierarchy)

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2-arg open() gone by default

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1-arg open()gone by default?

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Latin-1 autopromote off by default

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utf-8 everything by default

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A clean, simple meta-model with basic classes and methods

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No indirect object syntax by default

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But only if you declare “use v5.16”

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But only if you declare “use v5.18”

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But only if you declare “use v5.20”

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So, Why?

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Perl needs to be cleaner, simpler and easier to work with

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For users...

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...and for implementers

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Perl should run everywhere

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Why isn’t Perl 5 onother Runtimes?

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“There’s no spec”

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That didn’t stop Ruby

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“Only Perl 5 can parse Perl 5”

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That didn't stop PPI

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To survive, a desperate hacker needs to be able to reimplement Perl 5

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Thanks!

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How do we make this happen faster?

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Perl 5 Maint Fund

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perlfoundation.org

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Questions/Tomatoes?http://blog.fsck.com jesse@perl.org@obra

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About the name

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Our language is called Perl 5

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Perl 6 is ourprecociouskid sister

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I’m happy to talk about renaming Perl 5...

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...if you write me a second implementation

that passes the test suite

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