Hi,

I have a struct and want to extends its methods, like:

```d
struct Server
{
  string name;
  string ip;
  int port;
  string user;
}
```

extension method here:

```d
string prompt(ref in Server server)
{
   return server.user ~ "@" ~ server.ip ~ ":" ~ server.port;
}

```

and call it with UFSC:

```d
string p = server.prompt;
```

is this the correct way to use struct and UFCS? it does not seem to copy there.

On Tuesday, 1 July 2014 at 05:09:49 UTC, Puming wrote:
> Hi,
>
> I have a struct and want to extends its methods, like:
>
> ```d
> struct Server
> {
>   string name;
>   string ip;
>   int port;
>   string user;
> }
> ```
>
> extension method here:
>
> ```d
> string prompt(ref in Server server)
> {
>    return server.user ~ "@" ~ server.ip ~ ":" ~ server.port;
> }
>
> ```
should be `server.port.to!int`;
>
> and call it with UFSC:
>
> ```d
> string p = server.prompt;
> ```
>
> is this the correct way to use struct and UFCS? it does not seem to copy there.

On 06/30/2014 10:11 PM, Puming wrote:

> On Tuesday, 1 July 2014 at 05:09:49 UTC, Puming wrote:
>> Hi,
>>
>> I have a struct and want to extends its methods, like:
>>
>> ```d
>> struct Server
>> {
>>   string name;
>>   string ip;
>>   int port;
>>   string user;
>> }
>> ```
>>
>> extension method here:
>>
>> ```d
>> string prompt(ref in Server server)
>> {
>>    return server.user ~ "@" ~ server.ip ~ ":" ~ server.port;
>> }
>>
>> ```
> should be `server.port.to!int`;

I think it should actually be server.port.to!string;

>> is this the correct way to use struct and UFCS? it does not seem to
>> copy there.

I don't understand your question but I wanted to help others by making complete code from your messages:

import std.conv;

struct Server
{
    string name;
    string ip;
    int port;
    string user;
}

string prompt(ref in Server server)
{
    return server.user ~ "@" ~ server.ip ~ ":" ~ server.port.to!string;
}

void main()
{
    auto server = Server("bzzt", "192.168.0.1", 80, "nobody");
    string p = server.prompt;
}

Ali

On Tuesday, 1 July 2014 at 05:26:47 UTC, Ali Çehreli wrote:
> On 06/30/2014 10:11 PM, Puming wrote:
>
> > On Tuesday, 1 July 2014 at 05:09:49 UTC, Puming wrote:
> >> Hi,
> >>
> >> I have a struct and want to extends its methods, like:
> >>
> >> ```d
> >> struct Server
> >> {
> >>   string name;
> >>   string ip;
> >>   int port;
> >>   string user;
> >> }
> >> ```
> >>
> >> extension method here:
> >>
> >> ```d
> >> string prompt(ref in Server server)
> >> {
> >>    return server.user ~ "@" ~ server.ip ~ ":" ~ server.port;
> >> }
> >>
> >> ```
> > should be `server.port.to!int`;
>
> I think it should actually be server.port.to!string;
>
> >> is this the correct way to use struct and UFCS? it does not
> seem to
> >> copy there.
>
> I don't understand your question but I wanted to help others by making complete code from your messages:
>
> import std.conv;
>
> struct Server
> {
>     string name;
>     string ip;
>     int port;
>     string user;
> }
>
> string prompt(ref in Server server)
> {
>     return server.user ~ "@" ~ server.ip ~ ":" ~ server.port.to!string;
> }
>
> void main()
> {
>     auto server = Server("bzzt", "192.168.0.1", 80, "nobody");
>     string p = server.prompt;
> }
>
> Ali

Thanks, This code works and my question is that is this a good practice to use `ref in` with structs instead of traditional pointer syntax (which does not play well with UFCS though) ? Is there any perfomance implications with `ref in`? I tried that it does not seem to copy the parameter value, which is good for me:


```d
#!/usr/bin/rdmd

import std.stdio;

struct Server
{
	string name;
}

string prompt(ref in Server server)
{
	__server.name = "new name";
	return server.name ~ ">";
}

Server __server;

void main()
{
	__server.name = "old_name";

	writeln(__server.prompt);
}
```

which prints

```
newname>
```

meaning the `return server.name ~ ">"` code in promt is using a reference of __server instead of copying the value.

Puming:

> is this a good practice to use `ref in` with structs instead of traditional pointer syntax (which does not play well with UFCS though) ? Is there any perfomance implications with `ref in`? I tried that it does not seem to copy the parameter value,

A "ref" is equivalent to a pointer that can't be null, so performance is the same as using a pointer (so it's good for larger structs, but not good if your struct is tiny).

Bye,
bearophile

On Tuesday, 1 July 2014 at 07:53:27 UTC, bearophile wrote:
> Puming:
>
>> is this a good practice to use `ref in` with structs instead of traditional pointer syntax (which does not play well with UFCS though) ? Is there any perfomance implications with `ref in`? I tried that it does not seem to copy the parameter value,
>
> A "ref" is equivalent to a pointer that can't be null, so performance is the same as using a pointer (so it's good for larger structs, but not good if your struct is tiny).
>
> Bye,
> bearophile

Thanks for the clarification. Now I can safely assume ref is better than pointer here because it plays nicely with UFCS.

On 07/01/2014 03:21 AM, Puming wrote:

> I can safely assume ref is better than pointer here

I agree.

> because it plays nicely with UFCS.

I don't understand that part. :) The following is the same program with just two differences: prompt() takes a pointer and 'server' is a pointer.

import std.conv;

struct Server
{
    string name;
    string ip;
    int port;
    string user;
}

string prompt(Server * server)
{
    return server.user ~ "@" ~ server.ip ~ ":" ~ server.port.to!string;
}

void main()
{
    auto server = new Server("bzzt", "192.168.0.1", 80, "nobody");
    string p = server.prompt;
}

Ali

On Tuesday, 1 July 2014 at 13:53:12 UTC, Ali Çehreli wrote:
> On 07/01/2014 03:21 AM, Puming wrote:
>
> > I can safely assume ref is better than pointer here
>
> I agree.
>
> > because it plays nicely with UFCS.
>
> I don't understand that part. :) The following is the same program with just two differences: prompt() takes a pointer and 'server' is a pointer.
>
> import std.conv;
>
> struct Server
> {
>     string name;
>     string ip;
>     int port;
>     string user;
> }
>
> string prompt(Server * server)
> {
>     return server.user ~ "@" ~ server.ip ~ ":" ~ server.port.to!string;
> }
>
> void main()
> {
>     auto server = new Server("bzzt", "192.168.0.1", 80, "nobody");
>     string p = server.prompt;
> }
>
> Ali

Wow, I've tested with some other code and pointer did not work, maybe I got something else wrong. Anyway, it's nice to know pointers also works with UFCS :-)