On Friday, 21 August 2015 at 11:43:11 UTC, Steven Schveighoffer
wrote:
On 8/21/15 7:34 AM, "Marc =?UTF-8?B?U2Now7x0eiI=?=
<[email protected]>" wrote:
On Thursday, 20 August 2015 at 19:41:44 UTC, Jonathan M Davis
wrote:
On Thursday, 20 August 2015 at 17:50:11 UTC, Steven
Schveighoffer wrote:
if(arr != null)
Definitely don't do that. IMHO, "== null and "!= null" should
be
illegal. If you really want to check for null, then you need
to use
"is null" or "!is null", whereas if you want to check that an
array is
empty, check its length or call empty. By using "== null" or
"!=
null", you tend to give the false impression that you're
checking
whether the object or array is null - which is not what you're
actually doing.
I disagree. `is null` is the one that should be illegal. `is`
is
supposed to do a bitwise comparison, but `null` is usually
just a
pointer/reference, while a slice consists of both a reference
and a
length. Which of those are compared?
Both. null in this context is actually an array (with null
pointer and zero length).
null is technically a no-type placeholder (defaulting to void *
without context). In different contexts it means different
things.
arr is null -> both pointer and length are 0
arr == null -> arr contains the same elements that null
contains.
arr.ptr == null -> arr contains a null pointer (length could
technically be non-zero).
For all intents and purposes
arr is null
is equivalent to
arr.ptr is null
ptr is a read-only property, so you can only set the ptr to null
if you set the array to null by assigning it null explicitly or
by assigning it an array which is null. "is null" is how you're
supposed to check pointers and references for null - explicitly
comparing a class object to null with == is actually illegal -
and I see no reason that arrays should be any different.
Regardless, using "is null" actually checks for whether an array
is null, whereas "== null" checks whether it's empty and doesn't
care about the ptr value - which is _not_ what most programmers
are going to expect when you compare something against null.
- Jonathan M Davis
