Re: TDPL dictionary example - ERROR with dmd and gdc

[Andrei Alexandrescu]

On 12/24/2010 11:35 AM, Caligo wrote:
I've been following the examples in the book and on page 8 we have this:
import std.stdio;
import std.string;

void main(){

      size_t[string] dictionary;
     foreach(line; stdin.byLine()){
               foreach(word; splitter(strip(line))){
                           if(word in dictionary) continue;
                     auto newID = dictionary.length;
                           dictionary[word] = newID;
                     writeln(newID, '\t', word);
             }
     }
}

With the latest GDC, which I think uses the latest 2.051, I get this error:
dictionary.d:12: Error: associative arrays can only be assigned values
with immutable keys, not char[]

Someone told me on digitalmars-d.learn that it works with DMD, but I
just downloaded the latest DMD that was just released and I still get
the same error.

Is there a workaround to this? and why the error?

Yah, this has been a long-standing issue. dmd has accepted for a while 
the code but produced incorrect results. Since then the bug has been 
fixed to refuse compilation.

The problem is, line has type char[] and the map's key type is string, 
i.s. array of immutable char. To convert x to string you need to say 
either x.idup or to!string(x). In theory the compiler/library would be 
clever enough to do that automatically when necessary, but we decided 
against it for now.

So: replace dictionary[word] with either dictionary[word.idup] or 
dictionary[to!string(word)]. A future printing will correct this mistake.


Andrei