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digitalmars.D - Array of interfaces static initialization

reply Yossarian <xtauer01 stud.fit.vutbr.cz> writes:
Hello.
I've got following array:

typedef iObject[] paramList;

and following object architecture:

abstract class iObject { ... };
class associativeArray : iObject { ... };
class block : iObject { ... };
class cIrc   : block { ... };
class command : associativeArray { ... };

and have function
Run(paramList);

..

when I use (z.B.)

command c;
cIrc this;

Run([c, this]);

irc.d(278): Error: cannot implicitly convert expression (this) of type  
ghhd.irc.
cIrc to ghhd.irc.command

both command and irc could be easily upcast to iObject,
so I think that this is absolutely legal usage (bug ?), or I've badly  
understood the array initializer?

TIA

-- Yossarian
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Apr 18 2008
next sibling parent reply "Janice Caron" <caron800 googlemail.com> writes:
On 18/04/2008, Yossarian <xtauer01 stud.fit.vutbr.cz> wrote:

  Run([c, this]);


I think it should be

    Run([cast(iObject)c,this]);
Apr 18 2008
parent reply Yossarian <xtauer01 stud.fit.vutbr.cz> writes:
Dne Fri, 18 Apr 2008 20:26:34 +0200 Janice Caron <caron800 googlemail.com>  
napsal/-a:


 On 18/04/2008, Yossarian <xtauer01 stud.fit.vutbr.cz> wrote:

  Run([c, this]);


 I think it should be

     Run([cast(iObject)c,this]);



And what if the command object has overloaded opCast() operator? The  
explicit upcasts are forbidden then?

TIA

-- Yossarian
Tato zpráva byla vytvořena převratným poštovním klientem Opery:  
http://www.opera.com/mail/
Apr 18 2008
parent reply "Janice Caron" <caron800 googlemail.com> writes:
On 18/04/2008, Yossarian <xtauer01 stud.fit.vutbr.cz> wrote:

  And what if the command object has overloaded opCast() operator? The
 explicit upcasts are forbidden then?


    iObject temp = c;
    Run([temp,this]);
Apr 18 2008
parent Yossarian <xtauer01 stud.fit.vutbr.cz> writes:
Dne Fri, 18 Apr 2008 20:49:37 +0200 Janice Caron <caron800 googlemail.com>  
napsal/-a:


 On 18/04/2008, Yossarian <xtauer01 stud.fit.vutbr.cz> wrote:

  And what if the command object has overloaded opCast() operator? The
 explicit upcasts are forbidden then?


     iObject temp = c;
     Run([temp,this]);



I know that this is working, I used it as an hack, but it is exactly that  
I dont want to . :-)
Never mind, hope I won't need to read that code again.


Thank you all.
-- 
Tato zpráva byla vytvořena převratným poštovním klientem Opery:  
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Apr 18 2008
prev sibling parent "Steven Schveighoffer" <schveiguy yahoo.com> writes:
"Yossarian" wrote

 Hello.
 I've got following array:

 typedef iObject[] paramList;

 and following object architecture:

 abstract class iObject { ... };
 class associativeArray : iObject { ... };
 class block : iObject { ... };
 class cIrc   : block { ... };
 class command : associativeArray { ... };

 and have function
 Run(paramList);

 ..

 when I use (z.B.)

 command c;
 cIrc this;

 Run([c, this]);

 irc.d(278): Error: cannot implicitly convert expression (this) of type 
 ghhd.irc.
 cIrc to ghhd.irc.command

 both command and irc could be easily upcast to iObject,
 so I think that this is absolutely legal usage (bug ?), or I've badly 
 understood the array initializer?


Not so badly :)  Basically, the expression [c, this] is ambiguous to the 
compiler.  So it makes a decision and says whatever the type of the first 
element is the type of the array.  So it types this as command[2].  Then it 
can't implicitly convert cIrc to command automatically so it pukes.

Janice's solution tells the compiler how to declare the literal (as an 
iObject[])

What you don't realize is that the D language is structured to have 
context-free parsing, which means just because [c, this] is used as an 
argument to Run, which takes iObject[], doesn't matter.  The compiler looks 
at [c, this] without context and tries to determine the type just from those 
tokens.  This makes the compiler implementation much simpler, but makes the 
compiler less 'intuitive.'

-Steve
Apr 18 2008