• Tower Ty (4/4) Mar 30 2008 I dont understand casting well. I see the following line in a program
• Neil Vice (20/26) Mar 30 2008 The syntax "new Class(args)" constructs a new instance of a class on the...
• Tower Ty (3/3) Mar 30 2008 Thanks Neil

Tower Ty <tytower yahoo.com.au> writes:

I dont understand casting well. I see the following line in a program

obj[0] = cast(Object) new ArrayWrapperString(data);

Does ArrayWrapperString() exist in the Tango library  (I did not find it) or
does this automatically create an instance of new type and create the type too.
?
Where could I read up on this ?

"Neil Vice" <sardonicpresence gmail.com> writes:

"Tower Ty" <tytower yahoo.com.au> wrote in message 
news:fsp4ft$7no$1 digitalmars.com...
I dont understand casting well. I see the following line in a program

 obj[0] = cast(Object) new ArrayWrapperString(data);

 Does ArrayWrapperString() exist in the Tango library  (I did not find it) 
 or does this automatically create an instance of new type and create the 
 type too. ?
 Where could I read up on this ?

The syntax "new Class(args)" constructs a new instance of a class on the 
heap. This will allocate memory for the instance and call the constructor 
that takes the arguments that are supplied in the parenthises.

The syntax "cast(type)" is a unary prefix operator that takes one argument 
(in this case the newly constructed ArrayWrapperString instance) and 
explicitly casts in to a reference of type Type (in this case Object).

Given that all classes in D inherit implicitly from class Object and I 
believe you should be able to implicitly cast an instance to a reference to 
any ancestor class I'd be surprised if the explicit cast was necessary.

The ArrayWrapperString class must be defined, no automatic type-creation 
occurs, and given this is from a DWT example I can only assume that it is 
declared as part of that library, though as it uses Tango it could also be 
in there - I'm personally familiar with neither.

If it was me I'd:

    grep -R "ArrayWrapperString" *

wherever I'd put my Tango/DWT source files to look for the declaration given 
that some quick google/digitalmars searching proved relatively fruitless.

Hope that puts you on the right track.

Tower Ty <towerty msn.com.au> writes:

Thanks Neil
I found it as a alias added later
module dwt.dwthelper.utils;