rfc:stricter_implicit_boolean_coercions

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rfc:stricter_implicit_boolean_coercions [2022/05/30 17:22] – iquitorfc:stricter_implicit_boolean_coercions [2022/06/20 16:00] (current) – Change status to declined and close voting iquito
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 ====== PHP RFC: Stricter implicit boolean coercions ====== ====== PHP RFC: Stricter implicit boolean coercions ======
-  * Version: 1.8+  * Version: 1.9
   * Date: 2022-05-16   * Date: 2022-05-16
   * Author: Andreas Leathley, <a.leathley@gmx.net>   * Author: Andreas Leathley, <a.leathley@gmx.net>
-  * Status: Under Discussion+  * Status: Declined
   * First Published at: http://wiki.php.net/rfc/stricter_implicit_boolean_coercions   * First Published at: http://wiki.php.net/rfc/stricter_implicit_boolean_coercions
  
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 This RFC boils down to these questions: This RFC boils down to these questions:
  
-  * Are you losing information when you reduce a value like -375, "false" or NaN to true for a typed boolean? +  * Are you losing information when you reduce a value like -375, "false" or 0.01 to true for a typed boolean? 
-  * Would you want to know when a value like -375, "false" or NaN is given to a typed boolean in a codebase?+  * Would you want to know when a value like -375, "false" or 0.01 is given to a typed boolean in a codebase?
   * How likely is it that such a coercion is unintended?   * How likely is it that such a coercion is unintended?
   * What about other boolean coercions in PHP? (handled in the [[stricter_implicit_boolean_coercions#other_boolean_coercions_in_php|next section]])   * What about other boolean coercions in PHP? (handled in the [[stricter_implicit_boolean_coercions#other_boolean_coercions_in_php|next section]])
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 Typed booleans (arguments, returns, properties) as discussed in this RFC are not the only part of PHP where implicit boolean coercions happen. They also occur in expressions like ''if'', the ternary operator ''?:'', or logical operators ''&&'' / ''||''. Whenever an expression in that context is not clearly true or false it is implicitly coerced to true or false. Typed booleans (arguments, returns, properties) as discussed in this RFC are not the only part of PHP where implicit boolean coercions happen. They also occur in expressions like ''if'', the ternary operator ''?:'', or logical operators ''&&'' / ''||''. Whenever an expression in that context is not clearly true or false it is implicitly coerced to true or false.
  
-However in these expressions you can use any values and are not restricted to scalar types like with typed booleans:+Using strict_types is an established way to change how scalar type coercions work (by prohibiting any coercions) but it does not affect implicit boolean coercions in expressions. But even in coercive mode there is a big difference between boolean expressions and boolean type coercions:
  
 <PHP> <PHP>
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 </PHP> </PHP>
  
-Typed booleans behave differently compared to these expressions because they do not accept arrays, resources, objects and null. Further restricting typed booleans is therefore not a change which makes the language more inconsistent, on the contrary, it could be an opportunity to differentiate these two use cases from each other, as they often have different expectations already:+Typed booleans behave differently compared to boolean expressions because they do not accept arrays, resources, objects and null. Further restricting typed booleans is therefore not a change which makes the language more inconsistent, on the contrary, it could be an opportunity to differentiate these two use cases more clearly from each other, as they often have different expectations already:
  
 <PHP> <PHP>
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 ^ From bool    | always possible (coerced to "" or "1") | always possible (coerced to 0 or 1)                      | always possible (coerced to 0 or 1)         |                                  | ^ From bool    | always possible (coerced to "" or "1") | always possible (coerced to 0 or 1)                      | always possible (coerced to 0 or 1)         |                                  |
  
-This RFC would further reduce the gap between strict mode and coercive mode, as even in coercive mode no information would be lost when coercing a scalar value and only values that are reasonable are accepted (otherwise a deprecation notice is emitted). All allowed coercions can be reversed to end up with the original value or almost the same ("0" can become "" and vice versa) - that is something this RFC makes possible, as without this RFC reversing a coercion to boolean will often not lead back to the original value. These examples illustrate reversibility and the loss of information:+This RFC would further reduce the gap between strict mode and coercive mode, as even in coercive mode no information would be lost when coercing a scalar value and only values that are reasonable are accepted (otherwise a deprecation notice is emitted). All allowed coercions can be reversed to end up with the original value or almost the same ("0" can become "") - that is something this RFC makes possible, as without this RFC reversing a coercion to boolean will often not lead back to the original value. These examples illustrate reversibility and the loss of information:
  
 <PHP> <PHP>
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 function toFloat(float $a) { return $a; } function toFloat(float $a) { return $a; }
  
-toString(toBool('')); // '' is converted to false and then back to '' +toString(toBool('')); // '' is coerced to false and then back to '' 
-toInt(toBool(0)); // 0 converted to false and then back to 0 +toInt(toBool(0)); // 0 coerced to false and then back to 0 
-toFloat(toBool(0.0)); // 0.0 converted to false and then back to 0.0+toFloat(toBool(0.0)); // 0.0 coerced to false and then back to 0.0
  
 toString(toBool('success'));  toString(toBool('success')); 
-// => 'success' is converted to true and then back to '1' +// => 'success' is coerced to true and then back to '1' 
-// the deprecation notice of this RFC points out the loss of information+// the new deprecation notice of this RFC points out the loss of information
                                                            
 toInt(toBool(-33)); toInt(toBool(-33));
-// => -33 is converted to true and then back to 1 +// => -33 is coerced to true and then back to 1 
-// the deprecation notice of this RFC points out the loss of information+// the new deprecation notice of this RFC points out the loss of information
  
 toFloat(toBool(0.01));  toFloat(toBool(0.01)); 
-// => 0.01 is converted to true and then back to 1 +// => 0.01 is coerced to true and then back to 1 
-// the deprecation notice of this RFC points out the loss of information+// the new deprecation notice of this RFC points out the loss of information
                                              
 // Existing behavior leading to TypeErrors and deprecation notices: // Existing behavior leading to TypeErrors and deprecation notices:
 toFloat('success'); // TypeError, not a numeric string toFloat('success'); // TypeError, not a numeric string
 toInt('1.6'); // Deprecation notice because fractional part is lost toInt('1.6'); // Deprecation notice because fractional part is lost
-toString(['']); // TypeError, array cannot be coerced to string +toString(['']); // TypeError, array cannot be implicitly coerced to string 
-toBool(null); // TypeError, null cannot be coerced to bool+toBool(null); // TypeError, null cannot be implicitly coerced to bool
 </PHP> </PHP>
  
-Having as little information loss between scalar type coercions as possible makes them safer to use and more predictable, which is one of the goals of this RFC.+Having as little information loss as possible when coercing scalar types makes them safer to use and more predictable.
  
 ===== Implementation notes ===== ===== Implementation notes =====
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 </PHP> </PHP>
  
-With the many deprecation notices that appeared in PHP 8.0 and 8.1 there is some wariness if more deprecation notices are worth it. These are the arguments why the RFC author thinks it will not cause too much pain:+With the many deprecation notices that appeared in PHP 8.0 and 8.1 there is some wariness if new deprecation notices are worth it. These are the arguments why the RFC author thinks it will not cause too much pain:
  
   * Each individual case is easy to fix, the easiest (but also least useful) is to loosly compare a value to true ($value == true) instead of directly giving the value to a typed bool   * Each individual case is easy to fix, the easiest (but also least useful) is to loosly compare a value to true ($value == true) instead of directly giving the value to a typed bool
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 ===== Future Scope ===== ===== Future Scope =====
  
-While this RFC only targets boolean coercions when not using strict_types, the overall goal is to have a solid and easy-to-understand foundation of type coercions between scalar values, and coercions to booleans are the biggest missing piece when looking at that.+While this RFC only targets boolean coercions when not using strict_types, this is just the last missing piece for the overall goal of having a solid and easy-to-understand foundation of type coercions between scalar values.
  
-One benefit of these well-developed coercions could be to make them available in an explicit way to PHP developers. Having functions like ''is_coerceable_to_bool'' and ''coerce_to_bool'' (and with similar functions for int and float) that behave exactly as giving a value to a boolean argument could be useful when receiving input from a form or database. Compared to the current explicit type coercions (''(bool)'', ''boolval'', ''(int)'' or ''(float)'') this would allow only a certain subset of values instead of coercing any value, giving developers an effective way to make sure they are dealing with values that make sense - or fail early if an unexpected value is encountered. And because it is based on the type coercion behavior of PHP the learning curve would be low.+One benefit of these well-developed coercions could be to make them available in an explicit way to PHP developers. Having functions like ''is_coerceable_to_bool'' and ''coerce_to_bool'' (and with similar functions for int, float and string) that behave exactly as giving a value to a boolean argument could be useful when receiving input from a form or database. Compared to the current explicit type coercions (''(bool)'', ''boolval'', ''(int)'' or ''(float)'') this would allow only a certain subset of values instead of coercing any value, giving developers an effective way to make sure they are dealing with values that make sense - or fail early if an unexpected value is encountered. And because it is based on the type coercion behavior of PHP the learning curve would be low and the knowledge would be universally useful within the language.
  
-If this RFC is accepted I would likely follow up with a discussion about a way to invoke the implicit coercion behavior in an explicit way, which would make it available to PHP developers even when using strict_types.+An example of how these functions could look like can be found on Github in [[https://github.com/squirrelphp/scalar-types|squirrelphp/scalar-types]] (written in PHP). This is just a preliminary example that would need to be discussed further with a follow-up RFC.
      
 ===== Proposed PHP Version ===== ===== Proposed PHP Version =====
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   * Implicit boolean expressions (as used in if, ternary, logic operators) are not affected.   * Implicit boolean expressions (as used in if, ternary, logic operators) are not affected.
   * FILTER_VALIDATE_BOOLEAN in the filter extension is not affected.   * FILTER_VALIDATE_BOOLEAN in the filter extension is not affected.
 +  
 +===== Vote =====
 +
 +Voting started on 2022-06-06 and will end on 2022-06-20.
 +
 +<doodle title="Accept Stricter implicit boolean coercions RFC as proposed?" auth="iquito" voteType="single" closed="true">
 +   * Yes
 +   * No
 +</doodle>
  
 ===== Patches and Tests ===== ===== Patches and Tests =====
rfc/stricter_implicit_boolean_coercions.1653931361.txt.gz · Last modified: 2022/05/30 17:22 by iquito

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