Hello,
I want to make an alias to function "std.stdio.writeln" and "std.stdio.write" and use it like:

>static void log(bool newline = true)(string text)
>{
>    alias print(T...) = newline ? &writeln : &write;
> 
>    _file.print();
>    text.print();
>}

Unfortunately, it doesn't work... Also tried with "enum print ..." but also no success.
How to do it correctly?

On Monday, 20 August 2018 at 13:14:14 UTC, Andrey wrote:
Mistake... this is:
>static void log(bool newline = true)(string text)
>{
>    alias print(T...) = newline ? &writeln : &write;
> 
>    _file.print(text);
>    text.print();
>}

On Monday, 20 August 2018 at 13:22:02 UTC, Andrey wrote:
> On Monday, 20 August 2018 at 13:14:14 UTC, Andrey wrote:
> Mistake... this is:
>>static void log(bool newline = true)(string text)
>>{
>>    alias print(T...) = newline ? &writeln : &write;
>> 
>>    _file.print(text);
>>    text.print();
>>}

static void log(bool newline = true)(string text)
{
    static if(newline)alias print = writeln;
    else alias print = write;

    _file.print(text);
    text.print();
}

On Monday, 20 August 2018 at 13:14:14 UTC, Andrey wrote:
> Hello,
> I want to make an alias to function "std.stdio.writeln" and "std.stdio.write" and use it like:
>
>>static void log(bool newline = true)(string text)
>>{
>>    alias print(T...) = newline ? &writeln : &write;
>> 
>>    _file.print();
>>    text.print();
>>}
>
> Unfortunately, it doesn't work... Also tried with "enum print ..." but also no success.
> How to do it correctly?

Since newline is a compile-time parameter, you can use `static if`:

static if (newline) {
    alias print = writeln;
} else {
    alias print = write;
}

Note that since this alias is local to the function, you cannot use it with UFCS, so you will have to write `print(text)` instead of `text.print()`.

Full example: https://run.dlang.io/is/SrBJdk

On 08/20/2018 03:14 PM, Andrey wrote:
> Hello,
> I want to make an alias to function "std.stdio.writeln" and "std.stdio.write" and use it like:
> 
>> static void log(bool newline = true)(string text)
>> {
>>    alias print(T...) = newline ? &writeln : &write;
>>
>>    _file.print();
>>    text.print();
>> }
> 
> Unfortunately, it doesn't work... Also tried with "enum print ..." but also no success.
> How to do it correctly?

`writeln` is a template, so you can't do `&writeln`. You'd have to instantiate the template before you can get the function pointer: `&writeln!T`.

Even then you can't make an alias of that. `&writeln!T` is a function pointer, which is a value. But aliases work on types and symbols, not values.

If you manage to obtain aliases, you won't be able to use the ternary operator on them. Being an expression, `foo ? bar : baz` works on values. You can't use it with function aliases.

You have to commit to either function aliases or function pointers (values).

With aliases (no address-of operator, no ternary operator, `print` is not a template):

----
void log(bool newline = true)(string text)
{
   static if (newline) alias print = writeln;
   else alias print = writeln;
   print(text); /* Can't use UFCS with a local `print`, so `text.print()` doesn't work. */
}
----

With function pointers (have to instantiate `writeln`, `write`, and `print):

----
void log(bool newline = true)(string text)
{
    enum print(T ...) = newline ? &writeln!T : &write!T;

    print!string(text); /* No IFTI, because `print` isn't a function template. */
}
----

On Monday, 20 August 2018 at 13:35:07 UTC, ag0aep6g wrote:
> On 08/20/2018 03:14 PM, Andrey wrote:

Thanks everybody for your answers.

On Monday, 20 August 2018 at 13:14:14 UTC, Andrey wrote:
> Hello,
> I want to make an alias to function "std.stdio.writeln" and "std.stdio.write" and use it like:
>
>>static void log(bool newline = true)(string text)
>>{
>>    alias print(T...) = newline ? &writeln : &write;
>> 
>>    _file.print();
>>    text.print();
>>}
>
> Unfortunately, it doesn't work... Also tried with "enum print ..." but also no success.
> How to do it correctly?

If it's about having a concise syntax then you can do:

---
import std.stdio;

void main()
{
    log!false("meep ! ");
    log!true("meep meep !");
}

static void log(bool newline = true)(string text)
{
    alias print = (a) => newline ? writeln(a) : write(a);
    print(text);
}
---

although this is like static if {} () else {}