Re: [Vala] How do you get from the generic, to the.....specific?

2012-02-19 Thread Luca Bruno 
On Sun, Feb 19, 2012 at 5:32 AM, Matto Marjanovic  wrote:

> Are there any plans to add type bounds to Vala generics?
>
> This would allow something like (e.g., using Java's keyword):
>
> public int get_length  (T val) {
>  return val.length;
> }
>
>
Yes, but not anytime soon.

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Re: [Vala] How do you get from the generic, to the.....specific?

2012-02-18 Thread Matto Marjanovic 

On 02/18/12 15:10, ant wrote:

On 18 February 2012 21:56, Evan Nemerson  wrote:



public int get_length  (T val) {
  if ( typeof (T) == typeof (string) ) {
return ((string) val).length;
  } else {
GLib.error ("Unable to handle type `%s'", typeof (T).name ());
  }
}


Are there any plans to add type bounds to Vala generics?

This would allow something like (e.g., using Java's keyword):

public int get_length  (T val) {
  return val.length;
}

I.e. the T is qualified to be a subclass of 'string' (not that this is
necessarily possible in Vala), and thus the compiler knows that anything
that can be done to a string can be done to an instance of T.

-m



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Re: [Vala] How do you get from the generic, to the.....specific?

2012-02-18 Thread ant 
On 18 February 2012 21:56, Evan Nemerson  wrote:

Thanks for the comprehensive answer, it was most useful!

> You seem to be operating under a pretty fundamental (though
> understandable) misunderstanding about how Vala generics work.  This
> came up on stackoverflow recently, so you're not alone.

Heh, you're not wrong there!

> public int get_length (T val) {
>  if ( typeof (T) == typeof (string) ) {
>    return ((string) val).length;
>  } else {
>    GLib.error ("Unable to handle type `%s'", typeof (T).name ());
>  }
> }

Thanks, that's exactly what I was after.

cheers
ant
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[Vala] How do you get from the generic, to the.....specific?

2012-02-18 Thread ant 
Apologies for my confusedf terminology. I'm meeting with repeated
abysmal failure trying to bend generics to my will.

Going back to basics, I started with the example code at
https://live.gnome.org/Vala/Tutorial#Generics.

I had to rename set_data() and get_data() to get this to compile, but
that's no deal.

My simple goal is this: having created a wrapper, how do I
print it's length inside of set_thing(G data) ?? Or indeed access any
properties or methods of the specific 'G' thingy?

I can understand run-time errors if I instantiated a wrapper of some
non-gobject type, but the compile time error "the name 'get_type' does
not exist in the context of 'G'" has me baffled.

Here are my various attempts:


public class Wrapper : Object {
private G data;

public void set_thing(G data) {
this.data = data;

#if broken
var x = data.length;  /* can't use String methods */
#endif

#if broken
Type t = data.get_type(); /* can't use Object methods either... */
#endif

#if broken
G x = data;   /* No */
Type t = x.get_type();
#endif

#if broken
var x = (G)data;  /* No */
Type t = x.get_type();
#endif


#if segfault
var x = data as Object; /* Works so far... */
Type t = x.get_type();
stdout.printf("x is %p\n", x); /* seg fault */
#endif

#if illegal
var x = data as string; /* Operation not supported for type */
Type t = x.length;
#endif

#if segfault
var x = data as Object;
int l;
x.get("length", out l); /* seg fault */
#endif

}

public G get_thing() {
return this.data;
}
}

//

public static int main(string[] args) {

var wrapper = new Wrapper();
wrapper.set_thing("test");


return 0;
}



cheers
ant
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