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digitalmars.D.learn - Template classes

reply Andrew Spott <andrew.spott gmail.com> writes:
So, the attached is supposed to be a class that creates a vector of any type (I
would like it to only take numerical values (int, float, real, double, etc),
however, I am ok with it taking others (not that I see why someone would use it
that way).

I tried to compile it with the following, but it won't compile.  I don't really
understand the errors I'm getting either.

Can someone tell me what I'm doing wrong?  If you need more information, let me
know.

-Andrew

void testvector() {
	auto v = new Vector!(float)(3, 12.0);
	writefln(v.toString());
	int n = 0;
	
	while (n < n.size()) {
		v[n] = n;
	}
	
	writefln(v.toString());

}
Apr 14 2009
next sibling parent "Denis Koroskin" <2korden gmail.com> writes:
On Wed, 15 Apr 2009 01:01:28 +0400, Andrew Spott <andrew.spott gmail.com> wrote:


 So, the attached is supposed to be a class that creates a vector of any  
 type (I would like it to only take numerical values (int, float, real,  
 double, etc), however, I am ok with it taking others (not that I see why  
 someone would use it that way).

 I tried to compile it with the following, but it won't compile.  I don't  
 really understand the errors I'm getting either.

 Can someone tell me what I'm doing wrong?  If you need more information,  
 let me know.

 -Andrew

 void testvector() {
 	auto v = new Vector!(float)(3, 12.0);
 	writefln(v.toString());
 	int n = 0;
 	
 	while (n < n.size()) {
 		v[n] = n;
 	}
 	
 	writefln(v.toString());

 }


You've got quite a few errors in your code:

module vector;
private import std.string;

class Vector(T) {
private:
	T[] v;
//	int nn; // there is no need to store a size of array separately. It is
available as v.length
	
public:
	this() {
	}

	this(int n) {
//		nn = n; // not needed
		v = T[n]; // wrong, should be: v = new T[n];
	}

	this(int n, T a) {
//		nn = n;
		v = T[n]; // same here (see above)
		while (n > 0) { // v[] = a; is faster and does the same as the loop below
			n--;
			v[n] = a;
		}
	}

	T opIndex(int n, int m) { // this won't work, because float is not an array
		return v[n][m];   // try this: T opIndex(int n) { return v[n]; }
	}

	opIndexAssign(T)(T a, int n, int m) { // no need for a template, also you
forgot to write function return type
		v[n][m] = a;             // should be: void opIndexAssign(int n, T a) { v[n]
= a; }
	}

	int size() {
		return nn; // should be: return v.length;
	}

	string toString() {
		string s = "[";
		int n = 0;
		while ( n < nn) {
			s ~= v[n] ~ ", ";
		}
		return s ~ "]";
	}

	~this() { // no need for this one
	}
}


void testvector() {
	auto v = new Vector!(float)(3, 12.0);
	writefln(v.toString());
	int n = 0;
	
	while (n < n.size()) { // infinite loop
		v[n] = n;
	}
	
	writefln(v.toString());
 
}

Also, try using foreach instead of while and for loops.

For example,

string toString() {
    if (v.length == 0) return "[]";
    string s = "[";
    foreach (k; v[0..$-1]) {
        s = std.string.format("%s, %s", s, k);
    }
    s = std.string.format("%s, %s]", s, v[$-1]);
}

void testvector() {
    // ...
    foreach (index, ref value; v) {
        value = index;
    }
    // ...
}

Hope that helps.
Apr 14 2009
prev sibling parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Tue, 14 Apr 2009 17:01:28 -0400, Andrew Spott <andrew.spott gmail.com>  
wrote:


 So, the attached is supposed to be a class that creates a vector of any  
 type (I would like it to only take numerical values (int, float, real,  
 double, etc), however, I am ok with it taking others (not that I see why  
 someone would use it that way).

 I tried to compile it with the following, but it won't compile.  I don't  
 really understand the errors I'm getting either.

 Can someone tell me what I'm doing wrong?  If you need more information,  
 let me know.

 -Andrew

 void testvector() {
 	auto v = new Vector!(float)(3, 12.0);
 	writefln(v.toString());
 	int n = 0;
 	
 	while (n < n.size()) {
 		v[n] = n;
 	}
 	
 	writefln(v.toString());

 }


Try the attached (untested).

You might get some insight into how d should be written by looking at the  
changes.

BTW, if this is just an exercise fine, but your example is a completely  
redundant implementation of standard builtin arrays.

e.g., the following code does almost the same thing you are doing without  
requiring a new class:

void testvector() {
	auto v = new float[3];
	v[0..$] = 12.0;
	writefln(v);
	int n = 0;

	while(n < v.length) { // bug in original code
		v[n] = n;
		n++; // bug in original code
	}	
	
	writefln(v);
}


-Steve
Apr 14 2009
parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Tue, 14 Apr 2009 17:33:29 -0400, Steven Schveighoffer  
<schveiguy yahoo.com> wrote:


 e.g., the following code does almost the same thing you are doing without
 requiring a new class:


correction, the code does *exactly* the same thing you are doing.

-Steve
Apr 14 2009
parent reply Andrew Spott <andrew.spott gmail.com> writes:
yes, however there are going to be a few new classes that will be implemented
in this (dot products, cross products, etc)

Thanks for the help.

-Andrew

Steven Schveighoffer Wrote:


 On Tue, 14 Apr 2009 17:33:29 -0400, Steven Schveighoffer  
 <schveiguy yahoo.com> wrote:
 

 e.g., the following code does almost the same thing you are doing without
 requiring a new class:


 
 correction, the code does *exactly* the same thing you are doing.
 
 -Steve
Apr 14 2009
parent reply bearophile <bearophileHUGS lycos.com> writes:
Andrew Spott:

 yes, however there are going to be a few new classes that will be implemented
in this (dot products, cross products, etc)


You mean a few new methods.

Take a look at the 'this' of D2, it allows to create wrapper structs, so you
can just add methods to the built-in arrays.

Bye,
bearophile
Apr 14 2009
parent reply Arild Boes <aboesx gmail.com> writes:
bearophile skrev:

 Andrew Spott:

 yes, however there are going to be a few new classes that will be implemented
in this (dot products, cross products, etc)


 
 You mean a few new methods.
 
 Take a look at the 'this' of D2, it allows to create wrapper structs, so you
can just add methods to the built-in arrays.
 
 Bye,
 bearophile


Please elaborate on this. How does one do that?

/ab
Apr 15 2009
parent reply Jarrett Billingsley <jarrett.billingsley gmail.com> writes:
On Wed, Apr 15, 2009 at 12:13 PM, Arild Boes <aboesx gmail.com> wrote:


 Take a look at the 'this' of D2, it allows to create wrapper structs, so
 you can just add methods to the built-in arrays.

 Bye,
 bearophile


 Please elaborate on this. How does one do that?


With the new, delicious "alias this."

struct Array(T)
{
	T[] blah;
	alias blah this; // woo!
	
	void print()
	{
		writefln(blah);
	}
}

void main()
{
	Array!(int) x;
// anything not defined in Array will instead be looked up in the
'alias this' member
	x.length = 5;
	x[2] = 3;
	x.print();
}

Though actually I'm not sure why bearophile suggested this, since even
in D1, you can define 'extension' methods for arrays and AAs by simply
declaring a function that takes an array or AA as its first parameter.
 It's syntactic sugar for a normal function call.  By taking advantage
of templates and IFTI you can make these methods work for all kinds of
arrays.

void print(T)(T[] arr)
{
	writefln(arr);
}

void main()
{
	int[] x;
	x.length = 5;
	x[2] = 3;
	x.print(); // same as print(x);
}

This will work in D1 or D2.
Apr 15 2009
next sibling parent bearophile <bearophileHUGS lycos.com> writes:
Jarrett Billingsley:

 Though actually I'm not sure why bearophile suggested this,


The original poster seems to want to add some methods to a standard array. With
this you can give another module something that acts like an array that also
has such methods, or replaces them. With the old way you also need to import
the free functions into the other module...

Bye,
bearophile
Apr 15 2009
prev sibling parent reply Arild Boes <aboesx gmail.com> writes:
Jarrett Billingsley skrev:

 On Wed, Apr 15, 2009 at 12:13 PM, Arild Boes <aboesx gmail.com> wrote:
 

 Take a look at the 'this' of D2, it allows to create wrapper structs, so
 you can just add methods to the built-in arrays.

 Bye,
 bearophile


 Please elaborate on this. How does one do that?


 
 With the new, delicious "alias this."
 
 struct Array(T)
 {
 	T[] blah;
 	alias blah this; // woo!
 	
 	void print()
 	{
 		writefln(blah);
 	}
 }
 
 void main()
 {
 	Array!(int) x;
 // anything not defined in Array will instead be looked up in the
 'alias this' member
 	x.length = 5;
 	x[2] = 3;
 	x.print();
 }
 
 Though actually I'm not sure why bearophile suggested this, since even
 in D1, you can define 'extension' methods for arrays and AAs by simply
 declaring a function that takes an array or AA as its first parameter.
  It's syntactic sugar for a normal function call.  By taking advantage
 of templates and IFTI you can make these methods work for all kinds of
 arrays.
 
 void print(T)(T[] arr)
 {
 	writefln(arr);
 }
 
 void main()
 {
 	int[] x;
 	x.length = 5;
 	x[2] = 3;
 	x.print(); // same as print(x);
 }
 
 This will work in D1 or D2.


I see. Thank you very much for that answer.
Actually the f-call syntactic sugar seems like a good way to keep core 
classes of any library very lean and mean, whilst maintaining the 
ability to expand the module without re-compiling the original library! 
(just import this guy, and the new functions will be available to you as 
if declared in the original type).
Apr 16 2009
parent Jarrett Billingsley <jarrett.billingsley gmail.com> writes:
On Thu, Apr 16, 2009 at 1:14 PM, Arild Boes <aboesx gmail.com> wrote:


 Actually the f-call syntactic sugar seems like a good way to keep core
 classes of any library very lean and mean, whilst maintaining the ability to
 expand the module without re-compiling the original library! (just import
 this guy, and the new functions will be available to you as if declared in
 the original type).


Unfortunately it only works with arrays and AAs at the moment, though
the plan for D2 was to extend it to arbitrary types.

Some libraries (like Dog) do abuse the fact that it works on arrays,
though, by doing clever things like "typedef void[] Something;", and
you don't even know it's an array ;)
Apr 16 2009