Re: [Pyobjc-dev] caution with BOOL parameters

[Ronald O. <ous...@ci...>]

On Saturday, Mar 1, 2003, at 19:35 Europe/Amsterdam, Bob Pasker wrote:

> if you try to pass an int whose magnitude is greater than can
> be stored in a char (-256/+255), then you will get
>
> 	objc.error: depythonifying 'char', got int of wrong magnitude
>
> for example, with a table with greater than 255 rows, the following
> will fail:
>
>     self.theButton.setEnabled_(self.theTableView.numberOfRows())
>
> but
>
>     self.theButton.setEnabled_(self.theTableView.numberOfRows() != 0)
>
> works as expected. i assume (but haven't tested), that (say) delegate 
> methods
> which return a BOOL will also fail if the return value is outside the 
> range.
>
> also, one things i've done in my version of obj_support.m is to change 
> identical
> messages to different ones, e.g., changing 'depythonifying' to 
> 'depythonifyingN'
> so i can tell which constraint failed:
>
> 				ObjCErr_Set(ObjCExc_error,
> 					"depythonifying3 'char', got %s of "
> 					"wrong magnitude",
> 						argument->ob_type->tp_name);
>
> since python doesnt have a char datatype, one alternative is to relax 
> the
> constraint (in obj_support.m) that _C_CHR parameters must be within 
> range,
> and instead mask off all but the bottom 8 bits.

Boy am I glad I didn't apply a change I was thinking of ;-). I thought 
BOOL is an unsigned char and was thinking about changing the result of 
pythonifying a 'char' to a string of lenght 1 (what basicly is the 
corresponding "type" in Python).

I don't think masking of all but the bottom 8 bits would be a right 
idea. What if you want to return False from a method of a list of items 
is empty and True otherwise. The obvious mostly-pythonic way would be:
	def myMethod(self):
		return len(someList)

This would fail if the length of the list is a multiple of 256.

The right solution for this user-education, too bad we don't have a FAQ 
yet.

Ronald