There is a bug with the brand new warning system in D.
Bit is treated like an integer type, which it is *not*.

Simple test case:

> bit t() { return 1; }
> bit f() { return 0; }
> 
> void main()
> {
>   bit b = t() && f();
> }

"implicit conversion of expression (t() && f()) of
type int to bit can cause loss of data"

This code works fine:

> void main()
> {
>   bit b = true && false;
> }

(most likely because it is a compile-time expression?)


Converting any integer to a bit is *defined* as returning
0 for zero integers and 1 for non-zero integer values...

There is no "loss of data", as with going from int->short.

--anders

In article <d13hhd$126q$1@digitaldaemon.com>, =?ISO-8859-1?Q?Anders_F_Bj=F6rklund?= says...
>
>There is a bug with the brand new warning system in D.
>Bit is treated like an integer type, which it is *not*.
>
>Simple test case:
>
>> bit t() { return 1; }
>> bit f() { return 0; }
>> 
>> void main()
>> {
>>   bit b = t() && f();
>> }

I think the problem here is that binary opperators like &&, || and ! return int, not bit/bool. BTW, it this bug is fixed, I will start using warnings on a permanent basis, as they have already unveiled two serious bugs in my code (Thanks Walt!)

Nick

On Tue, 15 Mar 2005 15:46:20 +0000 (UTC), Nick wrote:

[snip]
> ... I will start using warnings on a
> permanent basis, as they have already unveiled two serious bugs in my code
> (Thanks Walt!)

Agreed. I've found a few bugs because of the warnings too. Thank you Walter for this helpful device.

-- 
Derek Parnell
Melbourne, Australia
16/03/2005 7:16:51 AM

One more on the subject:

int low, int high;

bool isEmpty()
{
   return low > hight;
}

Warning: "implicit conversion of expression (low > high) of type int to bit can cause loss of data".

Andrew.


"Anders F Björklund" <afb@algonet.se> wrote in message news:d13hhd$126q$1@digitaldaemon.com...
> There is a bug with the brand new warning system in D.
> Bit is treated like an integer type, which it is *not*.
>
> Simple test case:
>
>> bit t() { return 1; }
>> bit f() { return 0; }
>>
>> void main()
>> {
>>   bit b = t() && f();
>> }
>
> "implicit conversion of expression (t() && f()) of
> type int to bit can cause loss of data"
>
> This code works fine:
>
>> void main()
>> {
>>   bit b = true && false;
>> }
>
> (most likely because it is a compile-time expression?)
>
>
> Converting any integer to a bit is *defined* as returning
> 0 for zero integers and 1 for non-zero integer values...
>
> There is no "loss of data", as with going from int->short.
>
> --anders

On Tue, 15 Mar 2005 14:12:30 -0800, Andrew Fedoniouk wrote:

> One more on the subject:
> 
> int low, int high;
> 
> bool isEmpty()
> {
>    return low > hight;
> }
> 
> Warning: "implicit conversion of expression (low > high) of type int to bit can cause loss of data".
> 

This is not a bug.  The expression (low > high) results in an integer value
and it is possible to lose data when converting an integer to a bit (bool).

Now maybe such expressions should result in a true boolean value, but D does not support true boolean values, only pseudo-boolean values called bits ( a one-bit integer ).

Consequently, you cannot take the syntax shortcuts one would code in C/C++, and in D such expressions as above need to be spelled out in full ...

  return low > high : true ? false;


-- 
Derek
Melbourne, Australia
16/03/2005 9:27:15 AM

I suppose this has probably been discussed already, but does it really make sense for the result of a comparison to be an integer?

"Derek Parnell" <derek@psych.ward> wrote in message news:1abo3r0w4p3ct.1eds1mg8mobpz$.dlg@40tude.net...
> On Tue, 15 Mar 2005 14:12:30 -0800, Andrew Fedoniouk wrote:
>
>> One more on the subject:
>>
>> int low, int high;
>>
>> bool isEmpty()
>> {
>>    return low > hight;
>> }
>>
>> Warning: "implicit conversion of expression (low > high) of type int to
>> bit
>> can cause loss of data".
>>
>
> This is not a bug.  The expression (low > high) results in an integer
> value
> and it is possible to lose data when converting an integer to a bit
> (bool).
>
> Now maybe such expressions should result in a true boolean value, but D does not support true boolean values, only pseudo-boolean values called bits ( a one-bit integer ).
>
> Consequently, you cannot take the syntax shortcuts one would code in
> C/C++,
> and in D such expressions as above need to be spelled out in full ...
>
>  return low > high : true ? false;
>
>
> -- 
> Derek
> Melbourne, Australia
> 16/03/2005 9:27:15 AM

On Tue, 15 Mar 2005 21:49:49 -0500, Nick Sabalausky wrote:

> "Derek Parnell" <derek@psych.ward> wrote in message news:1abo3r0w4p3ct.1eds1mg8mobpz$.dlg@40tude.net...
>> On Tue, 15 Mar 2005 14:12:30 -0800, Andrew Fedoniouk wrote:
>>
>>> One more on the subject:
>>>
>>> int low, int high;
>>>
>>> bool isEmpty()
>>> {
>>>    return low > hight;
>>> }
>>>
>>> Warning: "implicit conversion of expression (low > high) of type int to
>>> bit
>>> can cause loss of data".
>>>
>>
>> This is not a bug.  The expression (low > high) results in an integer
>> value
>> and it is possible to lose data when converting an integer to a bit
>> (bool).
>>
>> Now maybe such expressions should result in a true boolean value, but D does not support true boolean values, only pseudo-boolean values called bits ( a one-bit integer ).
>>
>> Consequently, you cannot take the syntax shortcuts one would code in
>> C/C++,
>> and in D such expressions as above need to be spelled out in full ...
>>
>>  return low > high : true ? false;
> I suppose this has probably been discussed already, but does it really make sense for the result of a comparison to be an integer?
> 
Not to me. I think its plain daft. But I believe DMD does it this way because it tries to be compatible with (legacy) C/C++ code.

-- 
Derek
Melbourne, Australia
16/03/2005 1:58:09 PM

More importantly, it does it this way for reasons of processor optimization, to my understanding...

-[Unknown]


> On Tue, 15 Mar 2005 21:49:49 -0500, Nick Sabalausky wrote:
> 
> 
>>"Derek Parnell" <derek@psych.ward> wrote in message news:1abo3r0w4p3ct.1eds1mg8mobpz$.dlg@40tude.net...
>>
>>>On Tue, 15 Mar 2005 14:12:30 -0800, Andrew Fedoniouk wrote:
>>>
>>>
>>>>One more on the subject:
>>>>
>>>>int low, int high;
>>>>
>>>>bool isEmpty()
>>>>{
>>>>   return low > hight;
>>>>}
>>>>
>>>>Warning: "implicit conversion of expression (low > high) of type int to bit
>>>>can cause loss of data".
>>>>
>>>
>>>This is not a bug.  The expression (low > high) results in an integer value
>>>and it is possible to lose data when converting an integer to a bit (bool).
>>>
>>>Now maybe such expressions should result in a true boolean value, but D
>>>does not support true boolean values, only pseudo-boolean values called
>>>bits ( a one-bit integer ).
>>>
>>>Consequently, you cannot take the syntax shortcuts one would code in C/C++,
>>>and in D such expressions as above need to be spelled out in full ...
>>>
>>> return low > high : true ? false;
>>
>>I suppose this has probably been discussed already, but does it really make sense for the result of a comparison to be an integer?
>>
> 
> Not to me. I think its plain daft. But I believe DMD does it this way
> because it tries to be compatible with (legacy) C/C++ code.
> 

Derek Parnell wrote:

> This is not a bug.  The expression (low > high) results in an integer value
> and it is possible to lose data when converting an integer to a bit (bool).

As long as D uses pseudo-boolean casts to convert integers and pointers into bits, there is no possibility for "loss of data" when doing it...

The result is the same as : (integer != 0) or (pointer != null)

> Now maybe such expressions should result in a true boolean value, but D
> does not support true boolean values, only pseudo-boolean values called
> bits ( a one-bit integer ).

Well, bits are *not* 1-bit integers, but they sure are pseudo-booleans.

If you convert for instance the integer 256 into a byte, you get 0.
But if you convert the integer 2 into a bit, you get 1 (i.e. 'true')

--anders

PS.
It does not help that the spec says it *should* return a "bool":
> The result type of an OrOr expression is bool,
> The result type of an AndAnd expression is bool, Equality expressions ... The type of the result is bool.
> The is compares for ... The type of the result is bool.
> The result type of a relational expression is bool.
http://www.digitalmars.com/d/expression.html

Walter, can we get warnings that don't cause the compiler to error? I can't use -w for anything due to this int/bit conversion warning. I could change my code to avoid bit and pass ints around so that I can use the comparison operators with causing the compiler to freak out, but that seems like the wrong way to go. What is the recommended way to deal with -w and int/bit?

"Anders F Björklund" <afb@algonet.se> wrote in message news:d13hhd$126q$1@digitaldaemon.com...
> There is a bug with the brand new warning system in D.
> Bit is treated like an integer type, which it is *not*.
>
> Simple test case:
>
>> bit t() { return 1; }
>> bit f() { return 0; }
>>
>> void main()
>> {
>>   bit b = t() && f();
>> }
>
> "implicit conversion of expression (t() && f()) of
> type int to bit can cause loss of data"
>
> This code works fine:
>
>> void main()
>> {
>>   bit b = true && false;
>> }
>
> (most likely because it is a compile-time expression?)
>
>
> Converting any integer to a bit is *defined* as returning
> 0 for zero integers and 1 for non-zero integer values...
>
> There is no "loss of data", as with going from int->short.
>
> --anders