Iterating over an enum associative array

[spir]

On 03/14/2011 12:21 PM, Nebster wrote:
> Hey,
>
> I'm having some problems iterating over an enumerated associative array.
> It comes up with this error at compile time:
>>  Internal error: e2ir.c 4835
> I cut the code down to this:
>
>>  import std.stdio;
>>
>>  enum int[string] assoc = [";": 0, "=": 1, "+": 2, "-": 2, "*": 3, "/": 3];
>>
>>  void main()
>>  {
>>  foreach(op; assoc.byKey())
>>  writefln("op: %s", op);
>>  }
>
> What does this mean/how can I get this to work?

There are problems with associative array constants. I'm not 100% sure this is 
the source of your error, though. Anyway, the following works fine, using the 
module's "static this" constructor:

static int[string] assoc;
static this () {
     assoc = [";": 0, "=": 1, "+": 2, "-": 2, "*": 3, "/": 3];
}
static enum seq = [1,2,3];

unittest {
     foreach(op ; assoc.byKey())
         writefln("op: %s", op);
     foreach(n ; seq)
         writefln("n: %s", n);
}
==>
op: *
op: +
op: -
op: /
op: ;
op: =
n: 1
n: 2
n: 3

You can use this trick each time you need a D module to hold predefined and/or 
precomputed data (meaning, you need D to play the role of a data description 
language).
This is not needed if said data is plain simple literal values. As you see, dmd 
does not consider an associative array to be plain simple literal, even when it 
obviously is; but a sequential array, yes.


A side note: constant struct data can be directly defined at the module 
top-level, at least in simple cases. But (for any reason), dmd in fact does not 
create a single constant value that will be used everywhere you write its name. 
Instead, it re-creates the constant value at each place you write it. Aside the 
possible cost (?), this can create bugs if you count on it be unique:

struct S { int i; }
enum S* ps0 = &(S(0)), ps1 = &(S(1));

unittest {
     S* ps;
     if (true) ps = ps0; else ps= ps1;
     assert (*ps == *ps0);           // indeed
//~     assert (ps == ps0);         // fail !!!
     writefln("%s != %s", ps,ps0);   // BFC95FE4 != BFC95FF0
}

The trick of using the module's static this clause also solves this issue.

Denis
-- 
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