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Allow '??' on constant expressions #1868

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Allow '??' on constant expressions #1868

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marcioAlmada
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@marcioAlmada marcioAlmada commented Apr 17, 2016 •
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It looks like we forgot to allow the null coalesce operator on constant expressions https://3v4l.org/LoPsg:

<?php

const X = null ?? 2;

function($arg = null ?? 'foo') { return $arg; };

function() { static $var = null ?? 'foo'; return $var; };

new class { private $property = null ?? 'foo'; };

Fatal error: Constant expression contains invalid operations in /in/LoPsg on line 3

Reference https://wiki.php.net/rfc/const_scalar_exprs

marcioAlmada
marcioAlmada reviewed Apr 17, 2016
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Zend/zend_ast.c
zend_fetch_dimension_by_zval(&tmp, &op1, &op2);
if (ast->attr == ZEND_DIM_UNSET) {
/* @TODO fetch index without throwing the notice at Zend/zend_execute.c:1596 */
/* zend_fetch_dimension_address_UNSET(&tmp, &op1, &op2, IS_TMP_VAR); */
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@marcioAlmada marcioAlmada Apr 17, 2016 •
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^ is zend_fetch_dimension_address_UNSET the proper way to achieve this here?

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shouldn't that actually be an IS fetch?

@laruence laruence added the RFC label Apr 19, 2016
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@laruence should we really require RFC? This fits more in the 'bug' camp to me.

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bwoebi commented Apr 19, 2016

Nope, that looks like an oversight; there's definitely no ground for a RFC here.

@laruence laruence added Bug and removed RFC labels Apr 20, 2016
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okey, mark as bug

@marcioAlmada marcioAlmada force-pushed the bug/coalesce-const-expr branch from 99bc5cc to eaecc3e Compare April 20, 2016 22:00
@smalyshev
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What is this useful for? I have hard time seeing for what one would use such thing?

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marcioAlmada commented Apr 20, 2016 •
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@smalyshev if const X = A['foo'] ?: 2; already works, why shouldn't const X = A['foo'] ?? 2; work too?

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bwoebi commented Apr 20, 2016

@smalyshev constants can be arrays. May be useful in that case.

Also, this is not a question of why but rather of completeness.

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There should always be a question of why. But constant arrays looks like a good case, those can be defined elsewhere, that makes sense.

@marcioAlmada
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@bwoebi should be okay now :)

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Comment on behalf of bwoebi at php.net:

Merged via 672a995

@php-pulls php-pulls closed this Apr 20, 2016
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bwoebi commented Apr 20, 2016

Wrong commit, meant 9f3eab4...

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@marcioAlmada @bwoebi @laruence @smalyshev @php-pulls