Is using function() in templates possible at all?
I am trying to do a binary insert into my sorted array.
To sort classes and structs I would like to give a delegate `(t)
=> t.myValue` to sort on that value whitout having to implement
an interface or specifically declare opCmp for every class I want
to have sorted.
After all, I might want one group of objects of a given class
sorted in one way and another group of objects sorted on another
way depending on the usecase.
In C# this is done by passing on a lambda in for instance a LinQ
expression to sort such list after insertion, and is also usefull
in other circumstances.
But is it possible in D to do something simular but then pass on
this Function() during compile time?
something like
`
void main() { SortedList!(Vector3, (v) => v.y) list; }
struct Vector3 { float x, y, z; }
class SortedList(T, int function(T) comparer)
{
T[] array;
int foo(T t)
{
for(int i = 0; i < array.lenght; i++)
{
if(comparer(this.otherT) <= comparer(t))
{
//do stuff
array[i] = t;
}
}
}
}
`
Re: Is using function() in templates possible at all?
On Wednesday, 11 April 2018 at 21:07:03 UTC, Sjoerd Nijboer wrote:
class SortedList(T, int function(T) comparer)
I would say, alias template parameter is your friend.
https://dlang.org/spec/template.html#TemplateAliasParameter
´´´
import std.stdio;
import std.range;
void main()
{
auto list = new SortedList!(Vector3, v => v.y)();
assert(list.array.empty);
list.foo(Vector3.init);
}
struct Vector3 { float x, y, z; }
class SortedList(T, alias comparer)
{
T[] array;
auto foo(T t)
{
for(int i = 0; i < array.length; i++)
{
if(comparer(this.array[i]) <= comparer(t))
{
//do stuff
array[i] = t;
}
}
}
}
´´´
Re: Is using function() in templates possible at all?
On Wednesday, 11 April 2018 at 21:29:27 UTC, Alex wrote: I would say, alias template parameter is your friend. https://dlang.org/spec/template.html#TemplateAliasParameter class SortedList(T, alias comparer) It works, thank you! But just to be shure, there's no way to have this more strongly typed in D so I can enforce that `comparer`is a funciton or delegate with a specific defenition? Right now i'm relying on the template to error on some different place which might not give such a readable error message to the user.
Re: Is using function() in templates possible at all?
On Wednesday, 11 April 2018 at 22:13:33 UTC, Sjoerd Nijboer wrote:
On Wednesday, 11 April 2018 at 21:29:27 UTC, Alex wrote:
I would say, alias template parameter is your friend.
https://dlang.org/spec/template.html#TemplateAliasParameter
class SortedList(T, alias comparer)
It works, thank you!
But just to be shure, there's no way to have this more strongly
typed in D so I can enforce that `comparer`is a funciton or
delegate with a specific definition?
There is, with template constraints:
class SortedList(T, alias comparer) if(is(typeof(comparer(T.init)
: int))
{
//...
}
Re: Is using function() in templates possible at all?
On Thursday, 12 April 2018 at 00:05:26 UTC, Nicholas Wilson wrote:
There is, with template constraints:
class SortedList(T, alias comparer)
if(is(typeof(comparer(T.init) : int))
{
//...
}
If the function is declared with explicit parameter types:
```
auto list = new SortedList!(Vector3, (Vector3 v) => v.y)();
```
Then the template guard can even have a full type definition:
```
class SortedList(T, alias comparer)
if (is(typeof(comparer) : int function(T)))
{
//...
}
```
Re: Is using function() in templates possible at all?
On Thursday, 12 April 2018 at 11:17:01 UTC, Laurent Tréguier
wrote:
If the function is declared with explicit parameter types:
There are cool things possible, if the param type is explicitly
typed :)
´´´
import std.traits;
void main()
{
auto list = new SortedList!((Vector3 v) => v.y)();
list.foo(Vector3.init);
}
struct Vector3 { float x, y, z; }
class SortedList(alias comparer) if(is(ReturnType!comparer :
float))
{
alias T = Parameters!comparer[0];
T[] array;
auto foo(T t)
{
// do stuff
}
}
´´´
Re: Is using function() in templates possible at all?
On Thursday, 12 April 2018 at 11:53:21 UTC, Alex wrote:
On Thursday, 12 April 2018 at 11:17:01 UTC, Laurent Tréguier
wrote:
If the function is declared with explicit parameter types:
There are cool things possible, if the param type is explicitly
typed :)
´´´
import std.traits;
void main()
{
auto list = new SortedList!((Vector3 v) => v.y)();
list.foo(Vector3.init);
}
struct Vector3 { float x, y, z; }
class SortedList(alias comparer) if(is(ReturnType!comparer :
float))
{
alias T = Parameters!comparer[0];
T[] array;
auto foo(T t)
{
// do stuff
}
}
´´´
Getting rid of redundancy. Now that's nice !
