www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - "length" Symbol Conflict

reply Brian White <bcwhite precidia.com> writes:
Linux:  Digital Mars D Compiler v0.123

I came across an unexpected conflict between a local "length" variable 
and an internal one referring to an array size.  The following code 
demonstrates the problem:

ubyte[] foo(void* x, uint length)
{
   ubyte*  a = cast(ubyte*)x;
   ubyte[] b;
   b[0..length] = a[0..length];
   return b;
}

int main(char[][] args)
{
   char[] a = "abc";
   ubyte[] b;

   b = foo(a,3);
   printf("%.*s\n",b);
}

anchorage:~/tmp> dmd test.d && ./test
gcc test.o -o test -lphobos -lpthread -lm
Error: lengths don't match for array copy


It seems that "length" when used within the context of an array 
subscript takes on the length of the array instead of the value of the 
local variable.

As far as I can tell, this goes against D's basic design goals.  Since 
one is not allowed to even redefine a variable in a sub-block ("A block 
statement introduces a new scope for local symbols. A local symbol's 
name, however, must be unique within the function." 
[http://www.digitalmars.com/d/statement.html#block]), it seems 
unreasonable to have the compiler override an explicit local variable 
with an implicit internal one.

                                           Brian
                                  ( bcwhite precidia.com )

-------------------------------------------------------------------------------
                Computers make very fast, very accurate mistakes.
May 17 2005
parent reply Thomas Kuehne <thomas-dloop kuehne.thisisspam.cn> writes:
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Brian White schrieb am Tue, 17 May 2005 09:19:30 -0400:

<snip>

 It seems that "length" when used within the context of an array 
 subscript takes on the length of the array instead of the value of the 
 local variable.

 As far as I can tell, this goes against D's basic design goals.

<snip> Use the dollar sign ($) to access the array's length inside it's subscript and don't declare a "length" identifier in your code. The implicit "length" inside the subscript is scheduled for potential deprecation. Thomas -----BEGIN PGP SIGNATURE----- iD8DBQFCihNB3w+/yD4P9tIRAnyvAJ41QYqKWZTNLvHFqtrhfYWkbsauZgCeJ6YR HJ4FwcsKye+SrETXgRZZmuo= =3nv9 -----END PGP SIGNATURE-----
May 17 2005
parent reply Brian White <bcwhite precidia.com> writes:
It seems that "length" when used within the context of an array 
subscript takes on the length of the array instead of the value of the 
local variable.

As far as I can tell, this goes against D's basic design goals.

Use the dollar sign ($) to access the array's length inside it's subscript and don't declare a "length" identifier in your code. The implicit "length" inside the subscript is scheduled for potential deprecation.

Great! That's what I was getting at... The implicit "length" is going to cause confusion to a lot of people; it's a natural variable name to use. Brian ( bcwhite precidia.com ) ------------------------------------------------------------------------------- Idleness, indifference & irresponsibility are healthy responses to absurd work.
May 17 2005
parent "Charlie" <charles jwavro.com> writes:
 Great!  That's what I was getting at...  The implicit "length" is going
 to cause confusion to a lot of people; it's a natural variable name to

I agree, Im glad there taking it out :). Charlie "Brian White" <bcwhite precidia.com> wrote in message news:d6d1cs$3fv$1 digitaldaemon.com...
It seems that "length" when used within the context of an array
subscript takes on the length of the array instead of the value of the
local variable.

As far as I can tell, this goes against D's basic design goals.

Use the dollar sign ($) to access the array's length inside it's subscript and don't declare a "length" identifier in your code. The implicit "length" inside the subscript is scheduled for potential deprecation.

Great! That's what I was getting at... The implicit "length" is going to cause confusion to a lot of people; it's a natural variable name to

                                            Brian
                                   ( bcwhite precidia.com )

 --------------------------------------------------------------------------

 Idleness, indifference & irresponsibility are healthy responses to
 absurd work.

May 17 2005