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phantm:faq [2010/05/04 14:15]
philippe.suter created 		phantm:faq [2010/05/04 15:35]
ekneuss
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-====== FAQ ======+===== FAQ =====
  
-Plop?+Here is a list of common questions along with their answer.
  
-Plop+ 
 +==== What des "​phantm"​ mean? ==== 
 + 
 +//phantm// is an acronym of "PHp ANalzer for Type Mistakes"​ 
 + 
 + 
 + 
 +==== Why phantm? ==== 
 + 
 +We believe that even if PHP puts close to no restrictions on types, it is 
 +still interesting to verify that they are handled correctly. It is easy to 
 +identify patterns of type errors that are directly caused by programming mistakes. 
 +We thus bring some of the advantages of statically typed languages to PHP.  
 + 
 + 
 +==== I get lots of errors, does that mean my code is all wrong? ==== 
 + 
 +No. First of all, static analysis has its limitations. There will always be 
 +false positives given the semantics of PHP.  However, you can help //phantm// do 
 +a better job, by precisely annotating your code. See [[phantm:​annotations|Annotations]] for more 
 +details. 
 + 
 +Also, you'll notice that by default //phantm// is quite picky about uninitialized 
 +values, or implicit type conversions. 
 + 
 +For instance, on the code %%$a = "​2";​ echo $a / 2;%%, //phantm// will report that 
 +%%$a%% is not a valid operand for /. Even though those "​errors"​ are not 
 +critical and PHP itself handles them gracefully in most cases, it is still 
 +considered "bad style" by //​phantm//​. 
 + 
 + 
 +==== I get errors mentioning Top or Bottom, what are those types? ==== 
 + 
 +//phantm// represents types as so-called Lattice elements. In the type Lattice, 
 +''​Top''​ represents the supertype of all types, and ''​Bottom''​ represents the 
 +subtype of all PHP types. In short, ''​Top''​ means "Every possible types"​ 
 +(including uninitialized values) and ''​Bottom''​ means "No type"​. 
 + 
 + 
 + 
 +==== What is the difference between Top and Any ? ==== 
 + 
 +''​Any''​ represents types of defined values. However, the fact that a variable 
 +is undefined is represented as a type as well, namely ''​Uninitialized''​. ''​Any''​ 
 +does not include ''​Uninitialized'',​ but ''​Top''​ does. 
 + 
 + 
 + 
 +==== I have code that uses references, but it's not analyzed properly by phantm, why? ==== 
 + 
 +References are currently ignored by //​phantm//​. 
 + 
 + 
 +==== I get errors on my arrays, but the error itself is riddled with "​..."​s ? ==== 
 + 
 +//phantm// will try to reduce the size of errors as much as possible by 
 +limitting the string representation of types to the parts that are 
 +relevant for the type error. 
 + 
 + 
 +==== What is the Numeric type ? ==== 
 + 
 +''​Numeric''​ is simply ''​Float or Int''​. Unlike PHP's ''​is_numeric'',​ It does not 
 +include numeric string literals. 
 + 
 + 
 + 
 +==== I'm getting weird complicated types in my errors, with my unannotated code, why doesn'​t it say Any? ==== 
 + 
 +This is because //phantm// refine types used in expressions. For instance, given the code 
 + 
 +<​file>​ 
 +function foo($b) { 
 +    $a = $b / 2; // (1) 
 +    $c = $b / 3; // (2) 
 +} 
 +</​file>​ 
 + 
 +Before (1), ''​$b''​ is ''​Any''​ and thus issue an error since / expects two numeric 
 +types. ​ However, after (1), we can assume that ''​$b''​ is ''​Numeric''​. This is 
 +essential, as it dramatically reduces the number of errors! For instance, on 
 +(2), no error is issued. 
 + 
 +However, if ''​$b''​ is later used where a ''​String''​ is specifically required, you'​ll 
 +get an error looking like: ''​expected String, found Numeric''​. 
 + 
 + 
 +==== Can I ask phantm to focus on most interesting errors? ==== 
 + 
 +Yes! Usually, the option %%--quiet%% or even %%--shy%% will do a decent 
 +job on removing the least significant errors. Note however that it might potentially hide 
 +important notices.