[RFC][DISCUSSION] Match expression v2

  110243
May 22, 2020 11:08 tovilo.ilija@gmail.com (Ilija Tovilo)
Hi internals

I'd like to announce the match expression v2 RFC:
https://wiki.php.net/rfc/match_expression_v2

The goal of the new draft is to be as simple and uncontroversial as
possible. It differs from v1 in the following ways:

* Blocks were removed
* Secondary votes were removed
    * optional semicolon
    * omitting `(true)`
* Unimportant details were removed (e.g. examples for future scope)

You can look at the diff here:
https://github.com/iluuu1994/match-expression-rfc/pull/8/files

I will also leave the discussion period open for longer as that too
was one of the primary criticisms.

As mentioned by Kalle:

> Resurrecting rejected RFCs have a "cooldown" of 6 months: > https://wiki.php.net/rfc/voting#resurrecting_rejected_proposals
That is, unless:
> The author(s) make substantial changes to the proposal. While it's > impossible to put clear definitions on what constitutes 'substantial' > changes, they should be material enough so that they'll significantly > affect the outcome of another vote.
Given that many people have said without blocks they'd vote yes I'd say this is the case here. Let me know if you don't agree. Ilija
  110249
May 22, 2020 15:30 larry@garfieldtech.com ("Larry Garfield")
On Fri, May 22, 2020, at 6:08 AM, Ilija Tovilo wrote:
> Hi internals > > I'd like to announce the match expression v2 RFC: > https://wiki.php.net/rfc/match_expression_v2 > > The goal of the new draft is to be as simple and uncontroversial as > possible. It differs from v1 in the following ways: > > * Blocks were removed > * Secondary votes were removed > * optional semicolon > * omitting `(true)` > * Unimportant details were removed (e.g. examples for future scope) > > You can look at the diff here: > https://github.com/iluuu1994/match-expression-rfc/pull/8/files > > I will also leave the discussion period open for longer as that too > was one of the primary criticisms. > > As mentioned by Kalle: > > > Resurrecting rejected RFCs have a "cooldown" of 6 months: > > https://wiki.php.net/rfc/voting#resurrecting_rejected_proposals > > That is, unless: > > > The author(s) make substantial changes to the proposal. While it's > > impossible to put clear definitions on what constitutes 'substantial' > > changes, they should be material enough so that they'll significantly > > affect the outcome of another vote. > > Given that many people have said without blocks they'd vote yes I'd > say this is the case here. Let me know if you don't agree. > > Ilija
I'd say this is a textbook example of sufficiently "substantial." Thanks, Ilija! This looks a lot better. My one question is why you're not including the implicit "match (true)" in this version, when the secondary vote on the previous RFC was 80% in favor of it. (And I still think the argument is stronger if you include a comparison to ternary assignment, but that doesn't affect implementation.) --Larry Garfield
  110250
May 22, 2020 15:42 tovilo.ilija@gmail.com (Ilija Tovilo)
Hi Larry

> My one question is why you're not including the implicit "match (true)" > in this version, when the secondary vote on the previous RFC was > 80% in favor of it.
I received quite a bit of feedback that the RFC was too complex. I tried to make the RFC simpler by removing all non-essential parts. I'm ready to create a follow up RFC for this (although it would probably not make PHP 8.0).
> (And I still think the argument is stronger if you include a comparison > to ternary assignment, but that doesn't affect implementation.)
Makes sense, I will incorporate an example :) Ilija
  110264
May 22, 2020 23:32 larry@garfieldtech.com ("Larry Garfield")
On Fri, May 22, 2020, at 10:42 AM, Ilija Tovilo wrote:
> Hi Larry > > > My one question is why you're not including the implicit "match (true)" > > in this version, when the secondary vote on the previous RFC was > > 80% in favor of it. > > I received quite a bit of feedback that the RFC was too complex. I > tried to make the RFC simpler by removing all non-essential parts. I'm > ready to create a follow up RFC for this (although it would probably > not make PHP 8.0).
Hm. A logical argument, but given its overwhelming support before and that it's therefore almost certain to pass in the future, I don't see why it's a net win to have PHP 8.0 missing that bit. It seemed uncontroversial, and seems like a highly common use case. --Larry Garfield
  110292
May 28, 2020 15:57 tovilo.ilija@gmail.com (Ilija Tovilo)
Hi Larry

> > > My one question is why you're not including the implicit "match (true)" > > > in this version, when the secondary vote on the previous RFC was > > > 80% in favor of it. > > > > I received quite a bit of feedback that the RFC was too complex. I > > tried to make the RFC simpler by removing all non-essential parts. I'm > > ready to create a follow up RFC for this (although it would probably > > not make PHP 8.0). > > Hm. A logical argument, but given its overwhelming support before and that it's therefore almost certain to pass in the future, I don't see why it's a net win to have PHP 8.0 missing that bit. It seemed uncontroversial, and seems like a highly common use case.
80% were in favor of this feature but it's also worth noting that only 20 people have voted. To avoid risking another rejection and thus the RFC being delayed for a year I'd rather move the feature to a different RFC. Also, the feature being included in the first draft was a rash decision in the first place (completely my fault). There are multiple ways to deal with the value comparison (e.g. do type coercion like the switch or type-error on a non-boolean value) but they haven't been discussed at all. Ilija
  110252
May 22, 2020 15:44 ocramius@gmail.com (Marco Pivetta)
Hey Ilija,


On Fri, May 22, 2020 at 1:08 PM Ilija Tovilo ilija@gmail.com> wrote:

> Hi internals > > I'd like to announce the match expression v2 RFC: > https://wiki.php.net/rfc/match_expression_v2 > [...] > Given that many people have said without blocks they'd vote yes I'd > say this is the case here. Let me know if you don't agree. > > This looks exactly like the construct that I'd vote for: good work! :-)
Marco Pivetta http://twitter.com/Ocramius http://ocramius.github.com/
  110267
May 23, 2020 07:30 davey@php.net (Davey Shafik)
On Fri, May 22, 2020 at 4:09 AM Ilija Tovilo ilija@gmail.com> wrote:

> Hi internals > > I'd like to announce the match expression v2 RFC: > https://wiki.php.net/rfc/match_expression_v2 > > The goal of the new draft is to be as simple and uncontroversial as > possible. It differs from v1 in the following ways: > > * Blocks were removed > * Secondary votes were removed > * optional semicolon > * omitting `(true)` > * Unimportant details were removed (e.g. examples for future scope) > > You can look at the diff here: > https://github.com/iluuu1994/match-expression-rfc/pull/8/files > > I will also leave the discussion period open for longer as that too > was one of the primary criticisms. > > As mentioned by Kalle: > > > Resurrecting rejected RFCs have a "cooldown" of 6 months: > > https://wiki.php.net/rfc/voting#resurrecting_rejected_proposals > > That is, unless: > > > The author(s) make substantial changes to the proposal. While it's > > impossible to put clear definitions on what constitutes 'substantial' > > changes, they should be material enough so that they'll significantly > > affect the outcome of another vote. > > Given that many people have said without blocks they'd vote yes I'd > say this is the case here. Let me know if you don't agree. > > Ilija >
With these simplifications, I'm not entirely sure there is enough value here if the Conditional Return, Break, and Continue Statements RFC is passed. This could be written with the slightly more ugly, but serviceable: So this: $statement = match ($this->lexer->lookahead['type']) { Lexer::T_SELECT => $this->SelectStatement(), Lexer::T_UPDATE => $this->UpdateStatement(), Lexer::T_DELETE => $this->DeleteStatement(), default => $this->syntaxError('SELECT, UPDATE or DELETE'), }; could be expressed as: echo (function($match) { return $this->SelectStatement() if ($match === Lexer::T_SELECT); return $this->UpdateStatement() if ($match === Lexer::T_UPDATE); return $this->DeleteStatement() if ($match === Lexer::T_DELETE); return $this->syntaxError('SELECT, UPDATE or DELETE'); })($this->lexer->lookahead['type']); I mean, ultimately, it's equivalent to: echo (function($match) { if ($match === Lexer::T_SELECT) { return $this->SelectStatement() } if ($match === Lexer::T_UPDATE) { return $this->UpdateStatement() } if ($match === Lexer::T_DELETE) { return $this->SelectStatement() } return $this->syntaxError('SELECT, UPDATE or DELETE'); })($this->lexer->lookahead['type']); The main selling point for match is that it's more concise, I'm not convinced that the return if variant is much less concise. If you want to match more than one thing, use the OR (double pipe) operator in the if condition. Having said that… match is undeniably prettier. If we are doing this however, I'd prefer to implement Go's switch block, named match because we already have a switch. It's strict, but flexible. - Davey
  110293
May 28, 2020 16:12 tovilo.ilija@gmail.com (Ilija Tovilo)
Hi Davey

> I mean, ultimately, it's equivalent to: > > echo (function($match) { > if ($match === Lexer::T_SELECT) { > return $this->SelectStatement() > } > if ($match === Lexer::T_UPDATE) { > return $this->UpdateStatement() > } > if ($match === Lexer::T_DELETE) { > return $this->SelectStatement() > } > return $this->syntaxError('SELECT, UPDATE or DELETE'); > })($this->lexer->lookahead['type']); > > The main selling point for match is that it's more concise, I'm not convinced that the return if variant is much less concise. If you want to match more than one thing, use the OR (double pipe) operator in the if condition.
There is no ultimate right or wrong here. For myself, there's a lot of cognitive overhead reading the code above. For others that might not be the case. There are also some other benefits of using match, like the jumptable optimization and a smaller risk of making mistakes.
> If we are doing this however, I'd prefer to implement Go's switch block, named match because we already have a switch. It's strict, but flexible.
Since most people expressed a desire for the match expression with no blocks I wanted to introduce the expression first. After 6 months of using match opinions on blocks might change, or they might not. If we do introduce blocks match should be able to do pretty much everything Go's switch can. Ilija