[Discussion] Why can't I do "{$a::class}"? View as Markdown

Hi Internals,

Obviously we can't use constants or functions directly in strings using variable parsing, I assume because it lacks the easily detectable $.

However, we can use methods because the object variable has the $, which I assume is the reason methods work and functions don't.

I feel like it's something that could have been added when dynamic access of static members support was added in 5.3.0, but maybe it was overlooked or decided against? Consider:

<?php

$a = new A();

echo " {A::$static_property} \n"; // doesn't work (unless $static_property is a variable)
echo " {$a::$static_property} \n"; // works

echo " {A::static_method()} \n"; // doesn't work (just text)
echo " {$a::static_method()} \n"; // works

echo " {A::constant} \n"; // doesn't work
echo " {$a::constant} \n"; // doesn't work either, but why?

?>

Also, as a side note, why does this hack below work? It seems like something that would use eval(), but doesn't. Take a look:

https://3v4l.org/aPCSD

I found it at the bottom of the manual entry for Strings1. Not something I would use, but it's interesting to see.

Thanks,
Peter

In general, it would be nice to have some proper inline string
templating, like other languages (js, C#, etc). At least some way to
evaluate an expression and format. I'm thinking like in C#:

$"Price: {price:C2}, Quantity: {quantity}, Discount: {discount:P1},
Total after discount: {(price * quantity * (1 - discount)):N2}"

Price is formatted using currency with 2 decimal places, discount is
formatted using percentage and one decimal, and N is a number format
with 2 decimals.

Robert Landers
Software Engineer
Utrecht NL

Hi Peter

echo " {A::$static_property} \n"; // doesn't work (unless $static_property is a variable)
echo " {$a::$static_property} \n"; // works

echo " {A::static_method()} \n"; // doesn't work (just text)
echo " {$a::static_method()} \n"; // works

echo " {A::constant} \n"; // doesn't work
echo " {$a::constant} \n"; // doesn't work either, but why?

It would be straightforward to allow all expressions that start with a
$ in string interpolation, as I've noticed a couple of years ago
[1]. This restriction seems rather arbitrary.

I think I held off proposing this because I was planning on proposing
a more complete form of string interpolation [2]. However, the
backwards-compatible syntax was largely disliked, so I withdrew the
RFC.

I wasn't particularly fond of introducing more forms of strings (e.g.
$"", f"", etc.) to avoid the BC break, because there are already
plentiful:

• ''
• ""
• `` (yes, these allow interpolation)
• <<<HD ... HD
• <<<'HD' ... HD

Adding at least the two expected ones ($"" and $<<<HD ... HD) would
bump that up to 7 forms.

There were also suggestions to extend strings in a more generic way,
akin to JavaScripts template strings [3], but I didn't have any use
for this myself.

Ilija

[1] https://github.com/php/php-src/compare/master...iluuu1994:php-src:lift-variable-restriction-for-brace-dollar-string-interpolation

[2] https://wiki.php.net/rfc/arbitrary_string_interpolation

[3] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals

Hi Internals,

Obviously we can't use constants or functions directly in strings using
variable parsing, I assume because it lacks the easily detectable $.

However, we can use methods because the object variable has the $, which
I assume is the reason methods work and functions don't.

I feel like it's something that could have been added when dynamic
access of static members support was added in 5.3.0, but maybe it was
overlooked or decided against? Consider:

<?php

$a = new A();

echo " {A::$static_property} \n"; // doesn't work (unless $static_property
is a variable)
echo " {$a::$static_property} \n"; // works

echo " {A::static_method()} \n"; // doesn't work (just text)
echo " {$a::static_method()} \n"; // works

echo " {A::constant} \n"; // doesn't work
echo " {$a::constant} \n"; // doesn't work either, but why?

?>

Also, as a side note, why does this hack below work? It seems like
something that would use eval(), but doesn't. Take a look:

https://3v4l.org/aPCSD

I found it at the bottom of the manual entry for Strings1. Not
something I would use, but it's interesting to see.

Thanks,
Peter

Hi, Peter!

Also, as a side note, why does this hack below work?

It's not a hack. Variables, including callable ones with any arguments are
allowed to be interpolated. See another example: https://3v4l.org/BJUvL

Regards,
Valentin Udaltsov