Re: how to handle void arguments in generic programming ?

[Timon Gehr]

On 11/11/2013 04:52 AM, Timothee Cour wrote:
The code snippet below doesn't work. Is there a way to make it work?
import std.stdio;
void main(){
   writelnIfNonVoid(writeln("ok"));
}
void writelnIfNonVoid(T...)(T a){
   static if(T.length)
     writeln(a);
}


import std.stdio;
void main(){
    writelnIfNonVoid(writeln("ok"));
}
void writelnIfNonVoid(T...)(lazy T a){
    static if(T.length){
        static if(is(T[0]==void)) a[0];
        else write(a[0]);
        static if(T.length==1) writeln();
        else writelnIfNonVoid(a[1..$]);
    }
}

Or, if you care about evaluation order and locking stdout:

import std.stdio;

void main(){
    writelnIfNonVoid(writeln("ok"));
}
void writelnIfNonVoid(T...)(lazy T a){
    import std.range, std.algorithm, std.conv;
    mixin({
        string[] 
indices=iota(a.length).map!(i=>"a["~to!string(i)~"]").array~"cast(void)0";
        string r;
        foreach(i,t;T){
            if(is(t==void))
                indices[i+1]="("~indices[i]~","~indices[i+1]~")";
            else r~=indices[i]~",";
        }
        if(r.length) r="writeln("~r~");";
        return r~indices[$-1]~";";
    }());
}