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reply Jerome BENOIT <g6299304p rezozer.net> writes:
Hello List:

In tDlp book in section 5.6 entitled `Higher-Order Functions. Function Literals,
the first code example is:

-----------------------------------------------------------------
T[] find(alias pred, T)(T[] input)
	if (is(typeof(pred(input[0])) == bool)) {
	for(; input.length > 0; input = input[1 .. $]) {
		if (pred(input[0])) break;
		}
	return input;
	}
-----------------------------------------------------------------

I can play it. Nevertheless, it is not clear for me right now
what is the role played by `T' in the generic argument list (alias pred, T).
(Its meaning is bypassed in this section via a `deduction' way.)

Any hint is welcome.

Thanks in advance,
Jerome
Jan 20 2012
parent reply =?ISO-8859-1?Q?Alex_R=F8nne_Petersen?= <xtzgzorex gmail.com> writes:
On 20-01-2012 15:32, Jerome BENOIT wrote:

 Hello List:

 In tDlp book in section 5.6 entitled `Higher-Order Functions. Function
 Literals,
 the first code example is:

 -----------------------------------------------------------------
 T[] find(alias pred, T)(T[] input)
 if (is(typeof(pred(input[0])) == bool)) {
 for(; input.length > 0; input = input[1 .. $]) {
 if (pred(input[0])) break;
 }
 return input;
 }
 -----------------------------------------------------------------

 I can play it. Nevertheless, it is not clear for me right now
 what is the role played by `T' in the generic argument list (alias pred,
 T).
 (Its meaning is bypassed in this section via a `deduction' way.)

 Any hint is welcome.

 Thanks in advance,
 Jerome


It's important to realize that D does not have generics; rather, it has 
templates. What (alias pred, T) means is that it takes (virtually) any 
argument as the first template parameter (function literals included) 
and a type for the second parameter.

You can call this function like so:

auto ints = find!((x) { return x % 2 != 0; })([1, 2, 3, 4, 5]);

Here, the type parameter T gets deduced from the argument, which is an 
array of ints.

-- 
- Alex
Jan 20 2012
next sibling parent Jerome BENOIT <g6299304p rezozer.net> writes:
Thanks.

Let go further.


On 20/01/12 15:58, Alex R=F8nne Petersen wrote:

 On 20-01-2012 15:32, Jerome BENOIT wrote:

 Hello List:

 In tDlp book in section 5.6 entitled `Higher-Order Functions. Function=





 Literals,
 the first code example is:

 -----------------------------------------------------------------
 T[] find(alias pred, T)(T[] input)
 if (is(typeof(pred(input[0])) =3D=3D bool)) {
 for(; input.length > 0; input =3D input[1 .. $]) {
 if (pred(input[0])) break;
 }
 return input;
 }
 -----------------------------------------------------------------

 I can play it. Nevertheless, it is not clear for me right now
 what is the role played by `T' in the generic argument list (alias pre=




d,

 T).
 (Its meaning is bypassed in this section via a `deduction' way.)

 Any hint is welcome.

 Thanks in advance,
 Jerome


 It's important to realize that D does not have generics; rather, it has=


 templates. What (alias pred, T) means is that it takes (virtually) any a=
rgument as the first template parameter (function literals included) and =
a type for the second parameter.

 You can call this function like so:

 auto ints =3D find!((x) { return x % 2 !=3D 0; })([1, 2, 3, 4, 5]);

 Here, the type parameter T gets deduced from the argument, which is an =


array of ints.


What would be the non-deducible version ?

Jerome



 Jan 20 2012



prev sibling  parent reply Jerome BENOIT <g6299304p rezozer.net>  writes:


Hello Again:

On 20/01/12 15:58, Alex R=F8nne Petersen wrote:

 On 20-01-2012 15:32, Jerome BENOIT wrote:

 Hello List:

 In tDlp book in section 5.6 entitled `Higher-Order Functions. Function=





 Literals,
 the first code example is:

 -----------------------------------------------------------------
 T[] find(alias pred, T)(T[] input)
 if (is(typeof(pred(input[0])) =3D=3D bool)) {
 for(; input.length > 0; input =3D input[1 .. $]) {
 if (pred(input[0])) break;
 }
 return input;
 }
 -----------------------------------------------------------------

 I can play it. Nevertheless, it is not clear for me right now
 what is the role played by `T' in the generic argument list (alias pre=




d,

 T).
 (Its meaning is bypassed in this section via a `deduction' way.)

 Any hint is welcome.

 Thanks in advance,
 Jerome


 It's important to realize that D does not have generics; rather, it has=


 templates. What (alias pred, T) means is that it takes (virtually) any a=
rgument as the first template parameter (function literals included) and =
a type for the second parameter.

 You can call this function like so:

 auto ints =3D find!((x) { return x % 2 !=3D 0; })([1, 2, 3, 4, 5]);

 Here, the type parameter T gets deduced from the argument, which is an =


array of ints.

I am certainly still very confused here, but I guess it is important I ge=
t the point before to gig further D:
In (alias pred, T), are both `pred' and `T' parameters for the function f=
ind ? or is `T' some kind of parameter for `pred' ?

Thanks in advance,
Jerome =20






 Jan 20 2012



  parent reply =?ISO-8859-1?Q?Alex_R=F8nne_Petersen?= <xtzgzorex gmail.com>  writes:


On 20-01-2012 17:14, Jerome BENOIT wrote:

 Hello Again:

 On 20/01/12 15:58, Alex Rønne Petersen wrote:

 On 20-01-2012 15:32, Jerome BENOIT wrote:

 Hello List:

 In tDlp book in section 5.6 entitled `Higher-Order Functions. Function
 Literals,
 the first code example is:

 -----------------------------------------------------------------
 T[] find(alias pred, T)(T[] input)
 if (is(typeof(pred(input[0])) == bool)) {
 for(; input.length > 0; input = input[1 .. $]) {
 if (pred(input[0])) break;
 }
 return input;
 }
 -----------------------------------------------------------------

 I can play it. Nevertheless, it is not clear for me right now
 what is the role played by `T' in the generic argument list (alias pred,
 T).
 (Its meaning is bypassed in this section via a `deduction' way.)

 Any hint is welcome.

 Thanks in advance,
 Jerome


 It's important to realize that D does not have generics; rather, it
 has templates. What (alias pred, T) means is that it takes (virtually)
 any argument as the first template parameter (function literals
 included) and a type for the second parameter.

 You can call this function like so:

 auto ints = find!((x) { return x % 2 != 0; })([1, 2, 3, 4, 5]);

 Here, the type parameter T gets deduced from the argument, which is an
 array of ints.


 I am certainly still very confused here, but I guess it is important I
 get the point before to gig further D:
 In (alias pred, T), are both `pred' and `T' parameters for the function
 find ? or is `T' some kind of parameter for `pred' ?

 Thanks in advance,
 Jerome




Both pred and T are so-called template parameters. That is, they are 
statically resolved at compile time.

You could as well have called the function like so:

auto ints = find!((x) { return x % 2 != 0; }, int)([1, 2, 3, 4, 5]);

Notice how we have two parameter lists: The first one where we pass a 
function literal and the type int is the template parameter list. The 
second one is the actual runtime arguments to the function.

-- 
- Alex



 Jan 20 2012



  parent reply Jerome BENOIT <g6299304p rezozer.net>  writes:


On 20/01/12 17:23, Alex R=F8nne Petersen wrote:

 On 20-01-2012 17:14, Jerome BENOIT wrote:

 Hello Again:

 On 20/01/12 15:58, Alex R=F8nne Petersen wrote:

 On 20-01-2012 15:32, Jerome BENOIT wrote:

 Hello List:

 In tDlp book in section 5.6 entitled `Higher-Order Functions. Functi=








on

 Literals,
 the first code example is:

 -----------------------------------------------------------------
 T[] find(alias pred, T)(T[] input)
 if (is(typeof(pred(input[0])) =3D=3D bool)) {
 for(; input.length > 0; input =3D input[1 .. $]) {
 if (pred(input[0])) break;
 }
 return input;
 }
 -----------------------------------------------------------------

 I can play it. Nevertheless, it is not clear for me right now
 what is the role played by `T' in the generic argument list (alias p=








red,

 T).
 (Its meaning is bypassed in this section via a `deduction' way.)

 Any hint is welcome.

 Thanks in advance,
 Jerome


 It's important to realize that D does not have generics; rather, it
 has templates. What (alias pred, T) means is that it takes (virtually=






)

 any argument as the first template parameter (function literals
 included) and a type for the second parameter.

 You can call this function like so:

 auto ints =3D find!((x) { return x % 2 !=3D 0; })([1, 2, 3, 4, 5]);

 Here, the type parameter T gets deduced from the argument, which is a=






n

 array of ints.


 I am certainly still very confused here, but I guess it is important I=





 get the point before to gig further D:
 In (alias pred, T), are both `pred' and `T' parameters for the functio=




n

 find ? or is `T' some kind of parameter for `pred' ?

 Thanks in advance,
 Jerome




 Both pred and T are so-called template parameters.


Ok !

  That is, they are statically resolved at compile time.

 You could as well have called the function like so:

 auto ints =3D find!((x) { return x % 2 !=3D 0; }, int)([1, 2, 3, 4, 5])=


;

It is getting clearer in my mind.


 Notice how we have two parameter lists: The first one where we pass a f=


unction literal and the type int is the template parameter list. The seco=
nd one is the actual runtime arguments to the function.

I got this part of the story: I guess that I was confused by the alias.

Let assume that the predicate  must have now two parameters in such a way=
 that
the first is of type T and the second of type TM.

auto ff =3D find!((x, m) { return x % m !=3D 0; })([1, 2, 3, 4, 5]);

Here x would be of type T, and m of type TM.


What does look the code for find then ?

Thanks in advance,
Jerome






 Jan 20 2012



  parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com>  writes:


On 01/20/2012 08:43 AM, Jerome BENOIT wrote:


 -----------------------------------------------------------------
 T[] find(alias pred, T)(T[] input)
 if (is(typeof(pred(input[0])) == bool)) {
 for(; input.length > 0; input = input[1 .. $]) {
 if (pred(input[0])) break;
 }
 return input;
 }
 -----------------------------------------------------------------











 Let assume that the predicate must have now two parameters in such a way
 that
 the first is of type T and the second of type TM.

 auto ff = find!((x, m) { return x % m != 0; })([1, 2, 3, 4, 5]);

 Here x would be of type T, and m of type TM.


 What does look the code for find then ?


We must decide on what 'm' is on the find() line above. Do you want to 
provide it as a template parameter or a function parameter? Here is how 
it could be provided as a function parameter (the last '2' in the 
parameter list):

     auto ff = find!((x, m) { return x % m != 0; })([1, 2, 3, 4, 5], 2);

And here is a matching find() function template:

T[] find(alias pred, T, TM)(T[] input, TM m)
     if (is(typeof(pred(input[0], m)) == bool))
{
     for(; input.length > 0; input = input[1 .. $]) {
         if (pred(input[0], m)) break;
     }

     return input;
}

void main()
{
     auto ff = find!((x, m) { return x % m != 0; })([1, 2, 3, 4, 5], 2);
}

Notice that pred() now takes two parameters in find().


 Thanks in advance,
 Jerome





Philippe Sigaud's template document covers everything about templates:

   https://github.com/PhilippeSigaud/D-templates-tutorial

(Just download the pdf there.)

I have a chapter about templates which intentionally covers little, 
leaving the rest of templates to a later chapter:

   http://ddili.org/ders/d.en/templates.html

The problem is, 'alias' template parameters are in that later chapter, 
which hasn't been translated yet.

Ali



 Jan 20 2012



  parent  Tobias Pankrath <tobias pankrath.net>  writes:


 
 Philippe Sigaud's template document covers everything about templates:
 
    https://github.com/PhilippeSigaud/D-templates-tutorial
 
 (Just download the pdf there.)


This should be on the website. 



 Jan 20 2012