• Ellery Newcomer (8/8) Jan 07 2011 auto a = 1, b = null;
• Piotr Szturmaj (8/16) Jan 07 2011 Personally, I like it. In second line you specify int type, and list of
• Jonathan M Davis (7/20) Jan 07 2011 The second should definitely _not_ be allowed. * definitely goes with th...
• Lars T. Kyllingstad (5/18) Jan 10 2011 If I remember correctly, TDPL explicitly states that you may use
• Jonathan M Davis (7/25) Jan 10 2011 Well, it may. I don't know. I don't really believe in declaring multiple...
• bearophile (25/32) Jan 08 2011 I have discussed this with other people some time ago. At first I don't ...

Ellery Newcomer <ellery-newcomer utulsa.edu> writes:

auto a = 1, b = null;

int a = 1, *b = null;


The first is accepted by dmd, and it should result in typeof(a) == int 
and typeof(b) == void*. It is somewhat contradictory to the error 
message resulting from the second:

multiple declarations must have the same type, not int and int*

I am skeptical of dmd's permitting the first. Does anyone else see any 
utility in it?

Piotr Szturmaj <bncrbme jadamspam.pl> writes:

Ellery Newcomer wrote:
 auto a = 1, b = null;

 int a = 1, *b = null;


 The first is accepted by dmd, and it should result in typeof(a) == int
 and typeof(b) == void*. It is somewhat contradictory to the error
 message resulting from the second:

 multiple declarations must have the same type, not int and int*

 I am skeptical of dmd's permitting the first. Does anyone else see any
 utility in it?

Personally, I like it. In second line you specify int type, and list of 
*int* variables.
In first line you specify list of initialized variables which types 
should be inferred automatically. I see no reason why first line should 
not be permitted.
If one would need several variables of one type, why he wouldn't specify 
exact type instead of using 'auto'?

Jonathan M Davis <jmdavisProg gmx.com> writes:

On Friday, January 07, 2011 13:32:42 Ellery Newcomer wrote:
 auto a = 1, b = null;
 
 int a = 1, *b = null;
 
 
 The first is accepted by dmd, and it should result in typeof(a) == int
 and typeof(b) == void*. It is somewhat contradictory to the error
 message resulting from the second:
 
 multiple declarations must have the same type, not int and int*
 
 I am skeptical of dmd's permitting the first. Does anyone else see any
 utility in it? 

The second should definitely _not_ be allowed. * definitely goes with the type
in 
D (as it should have in C), not the variable. So, the *b = null makes no sense.

However, I'm vere suprised that the first one succeeds. I think that it should
be 
reported as a bug. All variables declared on the same line are supposed to have 
the same type.

- Jonathan M Davis

"Lars T. Kyllingstad" <public kyllingen.NOSPAMnet> writes:

On Fri, 07 Jan 2011 16:30:24 -0800, Jonathan M Davis wrote:

 On Friday, January 07, 2011 13:32:42 Ellery Newcomer wrote:
 auto a = 1, b = null;
 
 int a = 1, *b = null;
 
 
 [...]

 
 [...]
 
 However, I'm vere suprised that the first one succeeds. I think that it
 should be reported as a bug. All variables declared on the same line are
 supposed to have the same type.

If I remember correctly, TDPL explicitly states that you may use 
automatic type inference to declare variables of different types in one 
line.

-Lars

Jonathan M Davis <jmdavisProg gmx.com> writes:

On Monday 10 January 2011 01:59:34 Lars T. Kyllingstad wrote:
 On Fri, 07 Jan 2011 16:30:24 -0800, Jonathan M Davis wrote:
 On Friday, January 07, 2011 13:32:42 Ellery Newcomer wrote:
 auto a = 1, b = null;
 
 int a = 1, *b = null;
 
 
 [...]

 
 [...]
 
 However, I'm vere suprised that the first one succeeds. I think that it
 should be reported as a bug. All variables declared on the same line are
 supposed to have the same type.

 
 If I remember correctly, TDPL explicitly states that you may use
 automatic type inference to declare variables of different types in one
 line.

Well, it may. I don't know. I don't really believe in declaring multiple 
variables on one line in normal circumstances anyway. However, it's definitely
an 
inconsistency in the language, and I would be inclined to argue that it should 
be removed and TDPL errata-ed if it does mention this "feature." I don't see
any 
real benefit of allowing this.

- Jonathan M Davis

bearophile <bearophileHUGS lycos.com> writes:

Ellery Newcomer:

 int a = 1, *b = null;

Walter has disallowed code like this in D because in C it is a well known
source of bugs (so much that C style guides strongly suggest to declare only
each variable in a distinct statement and line of code).


 auto a = 1, b = null;

I have discussed this with other people some time ago. At first I don't like
this, it's against the D rule of not allowing different types to be initialized
in the same statement. It may cause some bugs.

Example: if you write a line of code like, meaning it to initialize six double
variables both you have a bug:
auto x1=1., x2=2., x3=3., x4=4., x5=5, x6=6.;

But you are playing with fire. Better to be safer and write:
double x1=1., x2=2., x3=3., x4=4., x5=5, x6=6.;

Or even:
double x1, x2, x3, x4, x5, x6;
x1 = 1.0;
x2 = 2.0;
x3 = 3.0;
x4 = 4.0;
x5 = 5.0;
x6 = 6.0;

Or:
double[6] x;
foreach (i, ref xi; x)
    xi = i + 1;

Or:
double[6] x = array(iota(1.0, 7.0));


 The first is accepted by dmd, and it should result in typeof(a) == int 
 and typeof(b) == void*. It is somewhat contradictory to the error 
 message resulting from the second:
 
 multiple declarations must have the same type, not int and int*

Error messages in DMD are a draft :-) I have opened many bug reports that
suggest to improve them.

Here the error message is not fully correct, but I think it's acceptable. To
improve it the D compiler may also give a number of the error, and a manual of
the errors may explain that indeed the "auto" is allowed to instantiate


Bye,
bearophile