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--- rfc:null_coercion_consistency [2022/05/07 08:53] – Example tweaks craigfrancis
+++ rfc:null_coercion_consistency [2022/05/11 12:07] – Update Future Scope to note difference in casting/converting vs coercion craigfrancis
@@ Line 114: / Line 114: @@
   - PHP 7.0 introduced the ability for user-defined functions to specify parameter types via the [[https://wiki.php.net/rfc/scalar_type_hints_v5#behaviour_of_weak_type_checks|Scalar Type Declarations RFC]], where the implementation triggered Type Errors for those using //strict_types=1//, and otherwise used coercion for string/int/float/bool, but not NULL.
   - PHP 8.1 updated internal function parameters to work in the same way.
+==== Scalar Types ====
+[[https://news-web.php.net/php.internals/117523|George Peter Banyard]] notes that "Userland scalar types [...] did not include coercion from NULL for //very// good reasons". The only reason mentioned in [[https://wiki.php.net/rfc/scalar_type_hints_v5|Scalar Type Declarations]] is "to be consistent with our existing type declarations" (no further details given).
+The RFC also says "it should be possible for existing userland libraries to add scalar type declarations without breaking compatibility", but this is not the case, because of NULL. This has made adoption of type declarations harder, as it does not work like the following:
+<code php>
+function my_function($s, $i, $f, $b) {
+  $s = strval($s);
+  $i = intval($i);
+  $f = floatval($f);
+  $b = boolval($b);
+  var_dump($s, $i, $f, $b);
+}
+function my_function(string $s, int $i, float $f, bool $b) {
+  var_dump($s, $i, $f, $b);
+}
+my_function(NULL, NULL, NULL, NULL);
+</code>
+Some developers view NULL as a missing/invalid value, and passing NULL to a function like //htmlspecialchars()// could indicate a problem (can a be useful check for static analysis, or in the context of //strict_types=1//).
 ==== Examples ====
@@ Line 131: / Line 155: @@
 $search = $request->getGet('q'); // CodeIgniter
-$value = array_pop($empty_array);
 $value = mysqli_fetch_row($result);
 $value = json_decode($json); // Invalid JSON, or nesting limit.
+$value = array_pop($empty_array);
 </code>
@@ Line 139: / Line 163: @@
 <code php>
+$rounded_value = round($value);
 $search_trimmed = trim($search);
@@ Line 315: / Line 341: @@
 ===== Backward Incompatible Changes =====
-None
+While the intention of this RFC is to avoid a BC break; for user defined functions to be updated to also coerce NULL (instead of throwing a Type Error), it's possible some code may rely on that behaviour, for example:
+<code php>
+function my_function(string $my_string) {
+  var_dump($my_string);
+}
+try {
+  my_function('A');   // string(1) "A"
+  my_function(1);     // string(1) "1"
+  my_function(1.2);   // string(3) "1.2"
+  my_function(true);  // string(1) "1"
+  my_function(false); // string(0) ""
+  my_function(NULL);  // Throw Type Error
+} catch (TypeError $e) {
+  // Do something important?
+}
+</code>
 ===== Proposed PHP Version(s) =====
@@ Line 338: / Line 381: @@
 "it's a bit late" - We only have a deprecation at the moment (which can and is being ignored), it will be "too late" when PHP 9.0 uses Fatal Errors.
-"Userland scalar types [...] did not include coercion from NULL for //very// good reasons." - The only reason mentioned in [[https://wiki.php.net/rfc/scalar_type_hints_v5|Scalar Type Declarations]] is "to be consistent with our existing type declarations" (no further details given). Talking to developers, the only reason mentioned is noted above, where NULL can be viewed as a missing/invalid value, and passing NULL to a function like //htmlspecialchars()// could indicate a problem (which can a be useful check for static analysis, or in the context of //strict_types=1//).
 The function //mt_rand()// can be called with no arguments, or with min and max integer arguments. A developer may call //mt_rand(NULL, NULL)// and expect it to work the same as no arguments (returning a random number between 0 and //mt_getrandmax()//), but the NULL's would be coerced to 0, so it would always return 0. That said, I cannot find any public examples of this happening ([[https://grep.app/search?q=mt_rand%28NULL&filter%5Blang%5D%5B0%5D=PHP|1]], [[https://grep.app/search?q=mt_rand%5Cs%2A%5C%28%5Cs%2ANULL&regexp=true&filter[lang][0]=PHP|2]], [[https://www.google.com/search?q=%22mt_rand+NULL+NULL%22|3]]).
@@ Line 351: / Line 392: @@
   - //$method// in [[https://php.net/method_exists|method_exists()]]
   - //$json// in [[https://php.net/json_decode|json_decode()]]
+It might be appropriate for coercion and explicit casting/converting to work in the same way, even if they were to become stricter in the values they accept; e.g. //intval("")// and //((int) "")// currently return int(0), whereas //(5 + "")// results in a TypeError.
 ===== Voting =====
@@ Line 368: / Line 411: @@
 ===== Notes =====
-The **15%** of scripts that do not use //strict_types=1// was calculated using [[https://grep.app/|grep.app]], to "search across a half million git repos", were each result is a script (not a count of matches,  [[https://grep.app/search?q=defuse/php-encryption&filter[lang][0]=PHP|example]]). We can see [[https://grep.app/search?q=strict_types&filter[lang][0]=PHP|272,871]] scripts using //strict_types=1//, out of [[https://grep.app/search?q=php&filter[lang][0]=PHP|1,842,666]]. And keep in mind that [[https://grep.app/search?q=class%20wpdb%20%7B&filter[lang][0]=PHP|WordPress only really appears once]], it is [[https://make.wordpress.org/core/2022/01/10/wordpress-5-9-and-php-8-0-8-1/#php-8-1-deprecation-passing-null-to-non-nullable-php-native-functions-parameters|affected by this deprecation]], and is installed/used by many.
+The **15%** of scripts that use //strict_types=1// was calculated using [[https://grep.app/|grep.app]], to "search across a half million git repos", were each result is a script (not a count of matches,  [[https://grep.app/search?q=defuse/php-encryption&filter[lang][0]=PHP|example]]). We can see [[https://grep.app/search?q=strict_types&filter[lang][0]=PHP|272,871]] scripts using //strict_types=1//, out of [[https://grep.app/search?q=php&filter[lang][0]=PHP|1,842,666]]. And keep in mind that [[https://grep.app/search?q=class%20wpdb%20%7B&filter[lang][0]=PHP|WordPress only really appears once]], it is [[https://make.wordpress.org/core/2022/01/10/wordpress-5-9-and-php-8-0-8-1/#php-8-1-deprecation-passing-null-to-non-nullable-php-native-functions-parameters|affected by this deprecation]], and is installed/used by many.
 In the [[https://wiki.php.net/rfc/scalar_type_hints_v5#behaviour_of_weak_type_checks|Scalar Type Declarations]] RFC for PHP 7.0, scalar types were defined as "int, float, string and bool" - but, despite NULL also being a simple value (i.e. not an array/object/resource), it was not included in this definition. For backwards compatibility reasons this definition is unlikely to change.

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