For PHP 7.4

https://www.php.net/manual/migration74.deprecated.php#migration74.deprecated.core.array-string-access-curly-brace

app/Core/Container.php

@@ -94,7 +94,7 @@ class Container
             $args[] = \is_numeric($k) ? $v : $this->resolve($v);
         }
         // Special case: reference to factory method
-        if ($class{0} == '@' && \strpos($class, ':') !== false) {
+        if ($class[0] == '@' && \strpos($class, ':') !== false) {
             list($name, $method) = \explode(':', \substr($class, 1), 2);
             $factory = $this->__get($name);
             $service = $factory->$method(...$args);
@@ -195,7 +195,7 @@ class Container
                         $value
                     );
                 }
-            } elseif (isset($value{0}) && $value{0} === '@') {
+            } elseif (isset($value[0]) && $value[0] === '@') {
                 return $this->__get(\substr($value, 1));
             }
         } elseif (\is_array($value)) {

app/Core/DBStatement.php

@@ -68,7 +68,7 @@ class DBStatement extends PDOStatement
             $bType = $this->types[$type];
             $bValue = $this->db->getValue($key, $params);
 
-            if ($type{0} === 'a') {
+            if ($type[0] === 'a') {
                 if (! \is_array($bValue)) {
                     throw new PDOException("Expected array: key='{$key}'");
                 }

app/Core/File.php

@@ -125,7 +125,7 @@ class File
 
         $name = \trim(\preg_replace('%[^\w.-]+%', '-', $name), '-');
 
-        if (! isset($name{0})) {
+        if (! isset($name[0])) {
             $name = (string) \time();
         }
 

app/Core/Files.php

@@ -112,7 +112,7 @@ class Files
         if (\is_string($value)) {
             $value = \trim($value, "Bb \t\n\r\0\x0B");
 
-            if (! isset($value{0})) {
+            if (! isset($value[0])) {
                 return 0;
             }
 

app/Core/Func.php

@@ -98,8 +98,8 @@ class Func
         $result = [];
         if (\is_dir($dir) && ($dh = \opendir($dir)) !== false) {
             while (($entry = \readdir($dh)) !== false) {
-                if (isset($entry{0})
-                    && $entry{0} !== '.'
+                if (isset($entry[0])
+                    && $entry[0] !== '.'
                     && \is_dir("{$dir}/{$entry}")
                     && \is_file("{$dir}/{$entry}/{$file}")
                 ) {

app/Core/Lang.php

@@ -120,7 +120,7 @@ class Lang
             $line = \trim($lines[$i]);
 
             // пустая строка
-            if (! isset($line{0})) {
+            if (! isset($line[0])) {
                 // промежуточные данные
                 if (isset($curComm)) {
                     $cur[$curComm] = $curVal;
@@ -178,11 +178,11 @@ class Lang
                 continue;
 
             // комментарий
-            } elseif ($line{0} == '#') {
+            } elseif ($line[0] == '#') {
                 continue;
 
             // многострочное содержимое
-            } elseif ($line{0} == '"') {
+            } elseif ($line[0] == '"') {
                 if (isset($curComm)) {
                     $curVal .= $this->originalLine($line);
                 }
@@ -255,7 +255,7 @@ class Lang
      */
     protected function originalLine($line)
     {
-        if (isset($line[1]) && $line{0} == '"' && $line{\strlen($line) - 1} == '"') {
+        if (isset($line[1]) && $line[0] == '"' && $line{\strlen($line) - 1} == '"') {
             $line = \substr($line, 1, -1);
         }
         return \str_replace(

app/Core/Mail.php

@@ -101,7 +101,7 @@ class Mail
         $local  = $matches[1];
         $domain = $matches[2];
 
-        if ('[' === $domain{0} && ']' === \substr($domain, -1)) {
+        if ('[' === $domain[0] && ']' === \substr($domain, -1)) {
             if (1 === \strpos($domain, 'IPv6:')) {
                 $prefix = 'IPv6:';
                 $ip     = \substr($domain, 6, -1);
@@ -509,7 +509,7 @@ class Mail
                 throw new SmtpException('Couldn\'t get mail server response codes.');
             }
             $response .= $get;
-            if (isset($get{3}) && $get{3} === ' ') {
+            if (isset($get[3]) && $get[3] === ' ') {
                 $return = \substr($get, 0, 3);
                 break;
             }

app/Core/Validator.php

@@ -472,7 +472,7 @@ class Validator
         if (null !== $value) {
             $this->addError('The :alias should be absent');
         }
-        if (isset($attr{0})) {
+        if (isset($attr[0])) {
             return $attr;
         } else {
             return null;

app/Models/Pages/Install.php

@@ -400,7 +400,7 @@ class Install extends Page
      */
     public function vCheckPrefix(Validator $v, $prefix)
     {
-        if (isset($prefix{0})) {
+        if (isset($prefix[0])) {
             if (! \preg_match('%^[a-z][a-z\d_]*$%i', $prefix)) {
                 $v->addError('Table prefix error');
             } elseif ('sqlite' === $v->dbtype && 'sqlite_' === \strtolower($prefix)) {