array.length++ not an lvalue

[Erik Lechak]

Koroskin Denis Wrote:

> On Wed, 18 Jun 2008 17:12:19 +0400, Erik Lechak <prochak at netzero.net>  
> wrote:
> 
> > Hello all,
> >
> > I just wanted to start by thanking you for the great responses to my  
> > previous questions.  I appreciate the knowledgeable and friendly nature  
> > of this newsgroup.
> >
> > I ran into my first WTF moment with D.  I spent way too much time  
> > figuring out why 'array'.length++ was a compiler error (Error: x.length  
> > is not an lvalue).
> >
> > This is a newsgroup entry describing the problem:
> > http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=39179
> >
> > Is there a document detailing these "special exceptions" so that I don't  
> > have to blindly stumble upon them?  If not are there any more that  
> > should be documented so that I can add them to my Wiki  
> > (http://www.lechak.info/wiki/index.php?title=D_Programming_Language)?
> >
> > For what it's worth, I think 'array'.length++ and 'array'.length += 1  
> > should be valid.  If that is not an option, it would be nice if the  
> > error message could be changed to something like "Error: x.length is a  
> > special property that prohibits the use of the increment (++) and  
> > add_and_assign (+=) operators".
> >
> > Thanks,
> > Erik Lechak
> >
> 
> Length property of the array is not a member variable, but rather a member  
> function:
> 

When I compile this:
import std.stdio;
void main(){
    int x[23];
    writefln(x.length());
}

I get this:
Error: undefined identifier length
Error: function expected before (), not length of type int

So the compiler is telling me length is of type int.

> int[] array = new int[42];
> assert(array.length() == 42);

This does not compile.

> but you can also omit paranthesis (that's merely a syntax sugar):

It's not syntactic sugar if it does not compile with the parens.

> assert(array.length == 42);

Yep, this works, but it does not show that array.length is a method/function.
 
> The same way the following:
> array.length = 100
> 
> is translated into a function call: array.length(100); which does array  
> resizing.

Ok.  Maybe it gets translated into a method call.  But that does not mean that array.length is a method.  It sounds more like a tied variable in perl.

> Note that you should normally call array.length(array.length() + 1)

I would love to do that because it makes sense.  But it does not compile.
 
> D *could* do the following trick:
> array.length()+=1 -> array.length(array.length() + 1);

array.length(array.length() + 1) is not a trick.  It is logical.

> but it would break too much of the existing code and makes a little of  
> sense.

It would break code but it would make sense at least to me:)
 
So I either have to look at properties as methods that are called without parens or integers that restrict my use of operators.  That's a bummer.

Thanks,
Erik Lechak