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Date: Mon, 12 Oct 2015 20:23:17 +0100
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Subject: Scalar type hints and scalar type name aliases cause confuson
From: ajf@ajf.me (Andrea Faulds)

Hi,

As PHP 7 currently is, if you write this:

     public function foo(): integer {
         return 12;
     }
     $bar = foo();

you'll get the following error:

     Fatal error: Uncaught TypeError: Return value of foo() must be an 
instance of integer, integer returned

Similarly, if you were to write this:

     public function foo(): boolean {
         return true;
     }
     $bar = $foo();

you'd get this:

     Fatal error: Uncaught TypeError: Return value of foo() must be an 
instance of boolean, boolean returned

These are confusing and unhelpful error messages. The long-form names of 
types (integer, boolean) aren't accepted as type hints, only their 
short-form names (int, bool) are. Yet we didn't reserve the names 
'integer' and 'boolean' so we could produce a helpful error message, so 
anyone who types these long names will have them interpreted as type 
hints for (likely non-existant) classes named 'integer' or 'boolean' 
respectively. That produces confusing error messages on its own, but 
worse, type hint errors use 'integer' and 'boolean' to describe the 
types of values expected or given. Together, these two issues mean you 
get the two incredibly confusing error messages above.

This is not kind to the users of PHP. It will cause unneeded confusion. 
This isn't even a theoretical case, that first example was based on a 
real StackOverflow question.[0] Mistakenly typing 'integer' or 'boolean' 
instead of 'int' and 'bool' is not at all an unlikely error, especially 
since the PHP manual uses these in some places (we should probably fix 
that at some point, and make it use PHP's actual syntax for return types 
and variadics, but I digress...), and since the aforementioned type 
error messages use them.

To avoid confusion, I would like it if we reserve 'integer' and 
'boolean' alongside 'int' and 'bool', and make them produce an error if 
used. This would catch out mistakes with people writing the wrong name 
for the type hint, and as a bonus would prevent people from misreading 
typehints for classes which actually have thse names, as no class with 
that name would be allowed. However, we're getting close to release and 
this might force some people to rename classes again if changed, causing 
disruption, so we might not be able to do this.

Alongside or instead of that, though, we can do two other things to make 
this situation better.

First, we could make type error messages use 'int' and 'bool'. This 
feels somewhat wrong to me since integer and Boolean are the proper 
English names for the types. But we do use the short names in some other 
places, like var_dump, so this isn't so bad. This way, we get this 
slightly clearer error:

     Fatal error: Uncaught TypeError: Return value of foo() must be an 
instance of integer, int returned

Second, we could add a helpful note to the TypeError message when the 
type hint is for a class named 'integer' or 'boolean' and the value 
passed was an integer or Boolean, respectively. My patch (based on 
Anthony's original) for the earlier Scalar Type Hinting with Cast RFC 
did this. This would make things even clearer:

     Fatal error: Uncaught TypeError: Return value of foo() must be an 
instance of integer, int returned (did you mean to use the type hint 'int'?)

Even if we can't reserve the names, I hope we can do the two other 
suggestions in time for release.

By the way, this situation is at least partly my fault. For PHP 7 I 
fixed zend_parse_parameters and userland type hint errors consistent 
with regard to type names: always 'integer', never 'long' (which only 
ever occured for the expectation, not what was actually given, 
bizarrely), and also always 'float', never 'double'. I also made sure 
is_int was an alias of is_long and not vice-versa. Alas, I made the 
mistake of picking 'int' over 'integer' and 'bool' over 'boolean'.

Anyway, can we do something about this soon?

Thanks!

[0] 
http://stackoverflow.com/questions/32665818/php-7-return-type-declarations-fatal-error

-- 
Andrea Faulds
http://ajf.me/