Question: Is there a sniff to detect the use of double quotes over single quotes?

[u01jmg3]

• Is there a current sniff to detect double quotes (unless string interpolation is in use) and instead recommend the use of single quotes? Small thing but curious if a sniff existed.
  • https://stackoverflow.com/questions/13620/speed-difference-in-using-inline-strings-vs-concatenation-in-php5#answer-13680

[aik099]

Can you please write example of that PHP code. Examples on provided link weren't clear.

[u01jmg3]

$x = "these are " . $foo;   //Warning

$y = "these are $foo";      //No warning
$z = 'these are ' . $foo;   //No warning

[aik099]

I saw that example, but since what's in $x and $z are equivalent, then why not just use single quotes. Also theoretically such string should work faster.

[u01jmg3]

Yep, indeed why not just singles quotes and yes it would be faster - anyway PHPCS could be used to enforce this?

[aik099]

Then back to original question in issue description: what is string interpolation?

I think sniff properly detects double quote usage, even in your example.

[u01jmg3]

Definition: In computer programming, string interpolation or variable substitution is the process of evaluating a string literal containing one or more placeholders, yielding a result in which the placeholders are replaced with their corresponding values.

String interpolation would be the example $y whereby double quotes would need to be used and PHPCS should give no warning.This is as well as $z giving no warning.

Which available sniff allows me to detect double quote usage as per $x?

[aik099]

I see, then Squiz.Strings.DoubleQuoteUsage is the one you need.

$x = "these are " . $foo; //warning

What warning message do you see? If you run phpcs with -s option, then also sniff code will be displayed.

[u01jmg3]

This is just what I'm looking for but it's also disallowing example $y. Anyway to tone down how strict PHPCS is and allow $y but prevent $x?

PHPCS warnings given in comments

$x = "these are " . $foo;   //String "these are " does not require double quotes; use single quotes instead
$y = "these are $foo";      //Variable "$foo" not allowed in double quote string; use concatenation instead
$z = 'these are ' . $foo;   //No warning

[gsherwood]

You can mute that specific error in your ruleset.xml file like this:

 <rule ref="Squiz.Strings.DoubleQuoteUsage.ContainsVar">
  <severity>0</severity>
 </rule>

Just by coincidence, this happens to be the exact example I picked for muting an error message on the annotated ruleset wiki page: https://github.com/squizlabs/PHP_CodeSniffer/wiki/Annotated-ruleset.xml

:)

Does that do what you are after?

[u01jmg3]

Thank you both

@gsherwood: thanks for answering my final question. I thought I was familiar with PHPCS but it seems I need to do some more reading! The snippet you've provided does exactly what I need it to.

[dbaltas]

This can be achieved with the following rule

<rule ref="Squiz.Strings.DoubleQuoteUsage.NotRequired" />

Which does not allow double quotes for plain strings but does allow them if they contain a variable.

[josephzidell]

In php 7, interpolation is actually faster than concatenation. Is there a reverse sniff that finds usages of concats-that-could-be-interpolations?

[gsherwood]

Maybe you want to comment on #2316

[josephzidell]

That one is about the quotes on an existing string. My use-case would be to detect single- or double-quoted strings that are currently concatenated and could use interpolation, which is basically a variable or class property (excludes constants, method calls).

[gsherwood]

Yes, but it may be more useful if a sniff that checks for single quote usage instead checks for concatenation. So if a sniff is to be written, I think it's worth putting your comments there for consideration rather than on this closed issue. Issue #2259 is probably also worth watching.

But I didn't answer your original question, which is no, there is no sniff to enforce the reverse that I know of.

[josephzidell]

Will do. Thanks