• mogu (12/12) May 12 2017 ```d
• Stanislav Blinov (4/16) May 12 2017 Boolean conversion on an array works on array's pointer, not it's
• mogu (16/34) May 12 2017 ```d
• Kagamin (4/5) May 14 2017 There was a lot of discussion about it:
• Yuxuan Shui (7/25) May 12 2017 However
• ag0aep6g (2/4) May 12 2017 String literals are null-terminated, so "" needs to point at a null byte...

mogu <mogucpp 163.com> writes:

```d
if (null)
     "1".writeln;
if ("")
     "2".writeln;
if ("" == null)
     "3".writeln;
```

Output:
2
3

How to understand this?

Stanislav Blinov <stanislav.blinov gmail.com> writes:

On Saturday, 13 May 2017 at 00:36:55 UTC, mogu wrote:
 ```d
 if (null)
     "1".writeln;
 if ("")
     "2".writeln;
 if ("" == null)
     "3".writeln;
 ```

 Output:
 2
 3

 How to understand this?

Boolean conversion on an array works on array's pointer, not it's 
length. So even though `"".length == 0`, `"".ptr != null`, and so 
`cast(bool)"" == true`.

mogu <mogucpp 163.com> writes:

On Saturday, 13 May 2017 at 00:59:14 UTC, Stanislav Blinov wrote:
 On Saturday, 13 May 2017 at 00:36:55 UTC, mogu wrote:
 ```d
 if (null)
     "1".writeln;
 if ("")
     "2".writeln;
 if ("" == null)
     "3".writeln;
 ```

 Output:
 2
 3

 How to understand this?

 Boolean conversion on an array works on array's pointer, not 
 it's length. So even though `"".length == 0`, `"".ptr != null`, 
 and so `cast(bool)"" == true`.

```d
string s1 = null;
string s2 = "";
assert(s1 == null);
assert(s1.ptr == null);
assert(s2 == null);
assert(s2.ptr != null);
if (s1)
     1.writeln;
if (s2)
     2.writeln;
```

Output:
2

Thanks very much. This is a little bit confusing.

Kagamin <spam here.lot> writes:

On Saturday, 13 May 2017 at 03:41:29 UTC, mogu wrote:
 Thanks very much. This is a little bit confusing.

There was a lot of discussion about it: 
https://issues.dlang.org/show_bug.cgi?id=4733, 
https://forum.dlang.org/thread/rrrtkfosfnfuybblexow forum.dlang.org

Yuxuan Shui <yshuiv7 gmail.com> writes:

On Saturday, 13 May 2017 at 00:59:14 UTC, Stanislav Blinov wrote:
 On Saturday, 13 May 2017 at 00:36:55 UTC, mogu wrote:
 ```d
 if (null)
     "1".writeln;
 if ("")
     "2".writeln;
 if ("" == null)
     "3".writeln;
 ```

 Output:
 2
 3

 How to understand this?

 Boolean conversion on an array works on array's pointer, not 
 it's length. So even though `"".length == 0`, `"".ptr != null`, 
 and so `cast(bool)"" == true`.

However

if ([])
     "1".writeln;

prints nothing.

So why does "" has non-null pointer while [] has null pointer? 
Looks inconsistent.

ag0aep6g <anonymous example.com> writes:

On 05/13/2017 06:20 AM, Yuxuan Shui wrote:
 So why does "" has non-null pointer while [] has null pointer? Looks
 inconsistent.

String literals are null-terminated, so "" needs to point at a null byte.