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digitalmars.D.learn - Variadic Template: cast problem

reply "Namespace" <rswhite4 googlemail.com> writes:
This code http://dpaste.dzfl.pl/6caed813 does only compile if i 
comment out the "Clone" method. Why? o.O
Aug 04 2012
parent reply Dmitry Olshansky <dmitry.olsh gmail.com> writes:
On 04-Aug-12 17:57, Namespace wrote:

 This code http://dpaste.dzfl.pl/6caed813 does only compile if i comment
 out the "Clone" method. Why? o.O


Because it calls constructor and fails? I've done substitution for you:
this(const vec!(float,2) values) {
		foreach (index, val; values) {
			this.values[index] = cast(T) val;
		}
	}

No big wonder.

I'd try to fix Clone to:
{
vec!(T, dim) tmp = void;
tmp.values = this.values;
return tmp;
}

-- 
Dmitry Olshansky
Aug 04 2012
parent reply "Namespace" <rswhite4 googlemail.com> writes:
On Saturday, 4 August 2012 at 14:05:32 UTC, Dmitry Olshansky 
wrote:

 On 04-Aug-12 17:57, Namespace wrote:

 This code http://dpaste.dzfl.pl/6caed813 does only compile if 
 i comment
 out the "Clone" method. Why? o.O


 Because it calls constructor and fails? I've done substitution 
 for you:
 this(const vec!(float,2) values) {
 		foreach (index, val; values) {
 			this.values[index] = cast(T) val;
 		}
 	}

 No big wonder.

 I'd try to fix Clone to:
 {
 vec!(T, dim) tmp = void;
 tmp.values = this.values;
 return tmp;
 }


Then temp is empty/null and you cannot assign anything to it.
Furthermore temp would get a reference to the original array.

And why it fails?
As i see, Clone calls this opCall method:
[code]
static vec!(T, dim) opCall(U, ubyte dim)(const vec!(U, dim) v) {
     return vec!(T, dim)(v.values);
}
[/code]

A simple workaround is to write

[code]
this(U...)(U values) {
	T[] temp;

	foreach (val; values) {
		temp ~= val;
	}

	foreach (index, val; temp) {
		this.values[index] = cast(T) val;
	}
}
[/code]

instead of

[code]
this() {
     foreach (index, val; values) {
	this.values[index] = cast(T) val;
     }
}
[/code]

But that seems weird to me.
Aug 04 2012
parent reply Dmitry Olshansky <dmitry.olsh gmail.com> writes:
n 04-Aug-12 18:16, Namespace wrote:

 On Saturday, 4 August 2012 at 14:05:32 UTC, Dmitry Olshansky wrote:

 On 04-Aug-12 17:57, Namespace wrote:

 This code http://dpaste.dzfl.pl/6caed813 does only compile if i comment
 out the "Clone" method. Why? o.O


 Because it calls constructor and fails? I've done substitution for you:
 this(const vec!(float,2) values) {
         foreach (index, val; values) {
             this.values[index] = cast(T) val;
         }
     }

 No big wonder.

 I'd try to fix Clone to:
 {
 vec!(T, dim) tmp = void;
 tmp.values = this.values;
 return tmp;
 }


 Then temp is empty/null and you cannot assign anything to it.
 Furthermore temp would get a reference to the original array.


Doh. I somehow totally expected fixed size vector to be value type (struct).


 And why it fails?
 As i see, Clone calls this opCall method:
 [code]
 static vec!(T, dim) opCall(U, ubyte dim)(const vec!(U, dim) v) {
      return vec!(T, dim)(v.values);
 }


Then more simple thing is:

return vec!(T, dim)(v.values[]);

Note the [].

Static arrays are not convertible to dynamic implicitly.
Your use of ~= probably does append all of one static array elements in 
one operation. To check it insert writeln in each iteration of your 
foreach loops, you might be surprised.


-- 
Dmitry Olshansky
Aug 04 2012
parent "Namespace" <rswhite4 googlemail.com> writes:
http://dpaste.dzfl.pl/ff58ffc5

I'm even more confused. o.O
Aug 04 2012