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digitalmars.D - Mixing C/D-style array declarations

reply bearophile <bearophileHUGS lycos.com> writes:
After a suggestion from simendsjo in D.learn, I have added an enhancement
request:
http://d.puremagic.com/issues/show_bug.cgi?id=5807

If you see something wrong in this post I will modify or close the enhancement
request.

The documentation about Postfix Array Declarations says:


 Rationale: The postfix form matches the way arrays are declared
 in C and C++, and supporting this form provides an easy migration
 path for programmers used to it.<


C style array declarations are handy (despite they add a little of extra
complexity and confusion to the D language).

But currently (DMD 2.052) D also supports a syntax like:

// array of 5 dynamic arrays of ints.
int[][5] c;
int[] c[5];
int c[5][];

What's the purpose of such mixed syntax?
1) It's not present in C programs;
2) It's not used in normal native D programs;
3) And in my opinion it's not good to use even during the migration from C to D
style, because it looks confusing (the order of ranges is inverted between C
and D syntax).

So I suggest to statically disallow such mixed syntax.


Currently the mixed syntax is not just useless and potentially confusing for
the programmer, it also causes problems with some vector operations:

void main() {
    int[] a1 = [1, 2, 3];
    int[] a2 = new int[3];
    a2[] = a1[];           // OK
    int[3] a3[] = a2[];    // line 5, Error
}

test.d(5): Error: cannot implicitly convert expression (a2[]) of type int[] to
int[3u][]

In theory if mixed C/D array declarations become disallowed, then there is only
one meaning for the operation at line 5. (This is not very nice, but I don't
see better solutions for this syntax problem with array operations).

Bye,
bearophile
Apr 03 2011
next sibling parent spir <denis.spir gmail.com> writes:
On 04/03/2011 07:43 PM, bearophile wrote:

 After a suggestion from simendsjo in D.learn, I have added an enhancement
request:
 http://d.puremagic.com/issues/show_bug.cgi?id=5807

 If you see something wrong in this post I will modify or close the enhancement
request.

 The documentation about Postfix Array Declarations says:


 Rationale: The postfix form matches the way arrays are declared
 in C and C++, and supporting this form provides an easy migration
 path for programmers used to it.<


 C style array declarations are handy (despite they add a little of extra
complexity and confusion to the D language).

 But currently (DMD 2.052) D also supports a syntax like:

 // array of 5 dynamic arrays of ints.
 int[][5] c;
 int[] c[5];
 int c[5][];

 What's the purpose of such mixed syntax?
 1) It's not present in C programs;
 2) It's not used in normal native D programs;
 3) And in my opinion it's not good to use even during the migration from C to
D style, because it looks confusing (the order of ranges is inverted between C
and D syntax).

 So I suggest to statically disallow such mixed syntax.


 Currently the mixed syntax is not just useless and potentially confusing for
the programmer, it also causes problems with some vector operations:

 void main() {
      int[] a1 = [1, 2, 3];
      int[] a2 = new int[3];
      a2[] = a1[];           // OK
      int[3] a3[] = a2[];    // line 5, Error
 }

 test.d(5): Error: cannot implicitly convert expression (a2[]) of type int[] to
int[3u][]

 In theory if mixed C/D array declarations become disallowed, then there is
only one meaning for the operation at line 5. (This is not very nice, but I
don't see better solutions for this syntax problem with array operations).


+++ D cleaning.

Denis
-- 
_________________
vita es estrany
spir.wikidot.com
Apr 03 2011
prev sibling next sibling parent reply "Vladimir Panteleev" <vladimir thecybershadow.net> writes:
On Sun, 03 Apr 2011 20:43:59 +0300, bearophile <bearophileHUGS lycos.com>  
wrote:


 C style array declarations are handy (despite they add a little of extra  
 complexity and confusion to the D language).


Hmm, I thought C-style array declarations are pending deprecation. I know  
the C-style function pointer syntax has already been deprecated.

-- 
Best regards,
  Vladimir                            mailto:vladimir thecybershadow.net
Apr 03 2011
parent bearophile <bearophileHUGS lycos.com> writes:
Vladimir Panteleev:


 Hmm, I thought C-style array declarations are pending deprecation.


Is this true? If this is true then I will close my new enhancement request.

Bye,
bearophile
Apr 03 2011
prev sibling parent Trass3r <un known.com> writes:
 Rationale: The postfix form matches the way arrays are declared
 in C and C++, and supporting this form provides an easy migration
 path for programmers used to it.<


 C style array declarations are handy (despite they add a little of extra  
 complexity and confusion to the D language).


Are you kidding?
It pollutes the grammar and breaks consistency.
The rationale is nonsense, it rather encourages people not to learn the D  
way to declare arrays.
Drop the C legacy!
Apr 03 2011