php variable interpolation inside variable [duplicate] - php

Question

Python has a feature called template strings.
>>> from string import Template
>>> s = Template('$who likes $what')
>>> s.substitute(who='tim', what='kung pao')
'tim likes kung pao'
I know that PHP allows you to write:
"Hello $person"
and have $person substituted, but the templates can be reused in various sections of the code?

Answer 1

You can use template strings like this:
$name = "Maria";
$info["last_name"] = "Warner";
echo "Hello {$name} {$info["last_name"]}";
This will echo Hello Maria Warner.

Answer 2

You could also use strtr:
$template = '$who likes $what';
$vars = array(
'$who' => 'tim',
'$what' => 'kung pao',
);
echo strtr($template, $vars);
Outputs:
tim likes kung pao

Answer 3

I think there are a bunch of ways to do this... but this comes to mind.
$search = array('%who%', '%what_id%');
$replace = array('tim', 'kung pao');
$conference_target = str_replace(
$search,
$replace,
"%who% likes %what%"
);
Ha, we even had one in our framework using vsprintf:
class Helper_StringFormat {
public static function sprintf($format, array $args = array()) {
$arg_nums = array_slice(array_flip(array_keys(array(0 => 0) + $args)), 1);
for ($pos = 0; preg_match('/(?<=%)\(([a-zA-Z_]\w*)\)/', $format, $match, PREG_OFFSET_CAPTURE, $pos);) {
$arg_pos = $match[0][2];
$arg_len = strlen($match[0][0]);
$arg_key = $match[1][0];
if (! array_key_exists($arg_key, $arg_nums)) {
user_error("sprintfn(): Missing argument '${arg_key}'", E_USER_WARNING);
return false;
}
$format = substr_replace($format, $replace = $arg_nums[$arg_key] . '$', $arg_pos, $arg_len);
$pos = $arg_pos + strlen($replace);
}
return vsprintf($format, array_values($args));
}
}
Which looks like it came from the sprintf page
This allows for calls like:
sprintfn('second: %(second)s ; first: %(first)s', array(
'first' => '1st',
'second'=> '2nd'
));
UPDATE
Here is an update to do what you want... not fully tested though
class Helper_StringFormat {
public static function sprintf($format, array $args = array()) {
$arg_nums = array_slice(array_flip(array_keys(array(0 => 0) + $args)), 1);
for ($pos = 0; preg_match('/(?<=%)\(([a-zA-Z_][\w\s]*)\)/', $format, $match, PREG_OFFSET_CAPTURE, $pos);) {
$arg_pos = $match[0][1];
$arg_len = strlen($match[0][0]);
$arg_key = $match[1][0];
if (! array_key_exists($arg_key, $arg_nums)) {
user_error("sprintfn(): Missing argument '${arg_key}'", E_USER_WARNING);
return false;
}
$format = substr_replace($format, $replace = $arg_nums[$arg_key] . '$', $arg_pos, $arg_len);
$pos = $arg_pos + strlen($replace); // skip to end of replacement for next iteration
}
return vsprintf($format, array_values($args));
}
}
$str = "%(my var)s now work with a slight %(my var2)s";
$repl = array("my var" => "Spaces", "my var2" => "modification.");
echo Helper_StringFormat::sprintf($str, $repl);
OUTPUT
Spaces now work with a slight modification.

Answer 4

Another more simple approach would be this:
$s = function ($vars) {
extract($vars);
return "$who likes $what";
};
echo $s(['who' => 'Tim', 'what' => 'King Pao']); // Tim likes King Pao
And yes, PHPStorm will complain...

Answer 5

I personally most like sprintf (or vsprintf, for an array of arguments). It places them in the intended order, coerces types as needed, and has a lot more advanced features available.
Example:
$var = sprintf("%s costs %.2f dollars", "Cookies", 1.1);
This will result in the value Cookies cost 1.10 dollars.
There's an entire family of printf functions for different use cases, all listed under "See Also".
Very versatile: same methods for providing variables, array components, function results, etc.

Answer 6

I made a function to do what you want. i made it "quck-and-dirty" because i have not much time to refactorize it, maybe i upload it to my github.
EDIT: a bug correction...
Use it like
formattemplatter(
'$who likes $what'
, array(
'who' => 'Tim'
, 'what' => 'Kung Pao'
)
);
Variables can be [a-zA-Z0-9_] only.
function formattemplater($string, $params) {
// Determine largest string
$largest = 0;
foreach(array_keys($params) as $k) {
if(($l=strlen($k)) > $largest) $largest=$l;
}
$buff = '';
$cp = false; // Conditional parenthesis
$ip = false; // Inside parameter
$isp = false; // Is set parameter
$bl = 1; // buffer length
$param = ''; // current parameter
$out = ''; // output string
$string .= '!';
for($sc=0,$c=$oc='';isset($string{$sc});++$sc,++$bl) {
$c = $string{$sc};
if($ip) {
$a = ord($c);
if(!($a == 95 || ( // underscore
($a >= 48 && $a <= 57) // 0-9
|| ($a >= 65 && $a <= 90) // A-Z
|| ($a >= 97 && $a <= 122) // a-z
)
)) {
$isp = isset($params[$buff]);
if(!$cp && !$isp) {
trigger_error(
sprintf(
__FUNCTION__.': the parameter "%s" is not defined'
, $buff
)
, E_USER_ERROR
);
} elseif(!$cp || $isp) {
$out .= $params[$buff];
}
$isp = $isp && !empty($params[$buff]);
$oc = $buff = '';
$bl = 0;
$ip = false;
}
}
if($cp && $c === ')') {
$out .= $buff;
$cp = $isp = false;
$c = $buff = '';
$bl = 0;
}
if(($cp && $isp) || $ip)
$buff .= $c;
if($c === '$' && $oc !== '\\') {
if($oc === '(') $cp = true;
else $out .= $oc;
$ip = true;
$buff = $c = $oc = '';
$bl = 0;
}
if(!$cp && $bl > $largest) {
$buff = substr($buff, - $largest);
$bl = $largest;
}
if(!$ip && ( !$cp || ($cp && $isp))) {
$out .= $oc;
if(!$cp) $oc = $c;
}
}
return $out;
}

Answer 7

Just for the sake of completeness: there is also Heredoc.
$template = fn( $who, $what ) => <<<EOT
$who likes $what
EOT;
echo( $template( 'tim', 'kung pao' ) );
Outputs:
tim likes kung pao
Sidenotes:
You get highlighting in your favourite language (if properly configured). Just substitute EOT (from the sample above) with whatever you like (e.c. HTML, SQL, PHP, ...).
Escape arrays with curly braces {$data['who']}. Accessing objekts like $data->who works without braces.
Arrow functions like fn($a)=>$a are available since PHP 7.4. You can write function($a){return $a;} if you are using PHP<7.4.