• "Simen kjaeraas" <simen.kjaras gmail.com> Jan 23 2010
• bearophile <bearophileHUGS lycos.com> Jan 23 2010
• Philippe Sigaud <philippe.sigaud gmail.com> Jan 23 2010
• "Simen kjaeraas" <simen.kjaras gmail.com> Jan 23 2010
• Philippe Sigaud <philippe.sigaud gmail.com> Jan 23 2010

"Simen kjaeraas" <simen.kjaras gmail.com> writes:

In attempting to create a function to initialize any array of structs in a  
simple manner, I created this code:

void fillArr( uint n, T, U... )( ref T[] arr, U args ) {
   arr[0] = T( U[0..n] );
   static if ( U.length > n ) {
     fillArr!( n )( arr[ 1..$ ], args[ n..$ ] );
   }
}

T[] initArray( T, uint n = U.length, U... )( U args ) if ( n > 0 ) {
   static if (
//      ( __traits( compiles, T( args[ 0..n ] ) ) ) && // Same as below.  
Added for completeness.
       ( is( typeof( T( args[ 0..n ] ) ) ) ) &&  // If we can instantiate a  
struct with this
       ( U.length % n == 0 )                     // and it matches the  
number of arguments,
       ) {
     T[] result = new T[ U.length / n ];         // Create an array
     fillArr!( n )( result, args );              // and fill it.
     return result;
   } else {
     return initArray!( T, n-1, U )( args );     // Didn't work. Try  
another parameter count.
   }
}

However, upon testing it with this code:

struct S {
   int n;
   string s;
}
auto s = initArray!( S )( 1, "a", 2, "b", 3, "c" );

I get this error:

foo.d(34): Error: cannot implicitly convert expression ((int _param_1,  
string _param_2)) of type (int _param_1, string _param_2) to int


The problem is apparently on this line:
   arr[0] = T( U[0..n] );
Though I am confuzzled as to why it does not work ( it works in initArray,  
line 2 ). Any ideas?

-- 
Simen

bearophile <bearophileHUGS lycos.com> writes:

Simen kjaeraas:

 In attempting to create a function to initialize any array of structs in a  
 simple manner,
 ...
 auto s = initArray!( S )( 1, "a", 2, "b", 3, "c" );


That syntax is not useful, if you have few more structs or fields you are lost
in the soup of commas and items..

Bye,
bearophile

Philippe Sigaud <philippe.sigaud gmail.com> writes:

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On Sat, Jan 23, 2010 at 14:44, Simen kjaeraas <simen.kjaras gmail.com>wrote:

 In attempting to create a function to initialize any array of structs in a
 simple manner, I created this code:

 void fillArr( uint n, T, U... )( ref T[] arr, U args ) {
  arr[0] = T( U[0..n] );
  static if ( U.length > n ) {
    fillArr!( n )( arr[ 1..$ ], args[ n..$ ] );
  }
 }


U is a type . U[0..n] is also a type. You should write:

arr[0]  = T(args[0..n]);


Maybe you could also use S.tupleof.length to get the number of fields in S
(or maybe there is a __traits which gives this) and avoid the recursion in
initArray:


void fillArr( T, U... )( ref T[] arr, U args ) {
 arr[0] =  T(args[0..T.tupleof.length]) ;
 static if ( U.length > T.tupleof.length ) {
   fillArr( arr[ 1..$ ], args[ T.tupleof.length..$ ] );
 }
}

T[] initArray( T, U... )( U args )
    if ( U.length > 0
    && (is(typeof( T( args[ 0..T.tupleof.length ] ) ) ) )
    && ( U.length % T.tupleof.length == 0 ))
{
   T[] result = new T[ U.length / T.tupleof.length ];         // Create an
array
   fillArr( result, args );              // and fill it.
   return result;
}

Philippe

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<br><br><div class=3D"gmail_quote">On Sat, Jan 23, 2010 at 14:44, Simen kja=
eraas <span dir=3D"ltr">&lt;<a href=3D"mailto:simen.kjaras gmail.com">simen=
.kjaras gmail.com</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote=
" style=3D"border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0=
.8ex; padding-left: 1ex;">
In attempting to create a function to initialize any array of structs in a =
simple manner, I created this code:<br>
<br>
void fillArr( uint n, T, U... )( ref T[] arr, U args ) {<br>
 =A0arr[0] =3D T( U[0..n] );<br>
 =A0static if ( U.length &gt; n ) {<br>
 =A0 =A0fillArr!( n )( arr[ 1..$ ], args[ n..$ ] );<br>
 =A0}<br>
}<br></blockquote><div><br>U is a type . U[0..n] is also a type. You should=
 write:<br><br>arr[0]=A0 =3D T(args[0..n]);<br><br><br>Maybe you could also=
 use S.tupleof.length to get the number of fields in S (or maybe there is a=
 __traits which gives this) and avoid the recursion in initArray:<br>
<br><br>void fillArr( T, U... )( ref T[] arr, U args ) {<br>=A0arr[0] =3D=
=A0 T(args[0..T.tupleof.length]) ;<br>=A0static if ( U.length &gt; T.tupleo=
f.length ) {<br>=A0=A0 fillArr( arr[ 1..$ ], args[ T.tupleof.length..$ ] );=
<br>=A0}<br>
}<br><br>T[] initArray( T, U... )( U args )<br>=A0=A0=A0 if ( U.length &gt;=
 0<br>=A0=A0=A0 &amp;&amp; (is(typeof( T( args[ 0..T.tupleof.length ] ) ) )=
 )<br>=A0=A0=A0 &amp;&amp; ( U.length % T.tupleof.length =3D=3D 0 ))<br>{<b=
r>=A0=A0 T[] result =3D new T[ U.length / T.tupleof.length ];=A0=A0=A0=A0=
=A0=A0=A0=A0 // Create an array<br>
=A0=A0 fillArr( result, args );=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 // a=
nd fill it.<br>=A0=A0 return result;<br>}<br><br><font color=3D"#888888">
</font></div></div>Philippe<br><br>

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"Simen kjaeraas" <simen.kjaras gmail.com> writes:

On Sat, 23 Jan 2010 18:09:26 +0100, Philippe Sigaud  =

<philippe.sigaud gmail.com> wrote:

 On Sat, Jan 23, 2010 at 14:44, Simen kjaeraas  =


 <simen.kjaras gmail.com>wrote:

 In attempting to create a function to initialize any array of structs=





 in a
 simple manner, I created this code:

 void fillArr( uint n, T, U... )( ref T[] arr, U args ) {
  arr[0] =3D T( U[0..n] );
  static if ( U.length > n ) {
    fillArr!( n )( arr[ 1..$ ], args[ n..$ ] );
  }
 }


 U is a type . U[0..n] is also a type. You should write:


Thank you! Darn, I should have been able to see that.

 Maybe you could also use S.tupleof.length to get the number of fields =



 S


Yeah, I could. However, S might use a different constructor, taking a
different number of arguments.

As for bearophile's concerns:
   struct simpleTuple( T... ) {
     T payload;
   }

   simpleTuple!( T ) =E0=BA=95( T... )( T args ) {
     return simpleTuple!( args );
   }

   T[] initArray( T, U... )( U args ) if ( is( typeof( T( args[0].tupleo=
f )  =

) ) && allSame!( U ) ) {
     T[] result =3D new T[ U.length ];
     foreach ( i, arg; args ) {
       result[ i ] =3D T( arg.tupleof );
     }
     return result;
   }

   struct S {
     int n;
     string s;
   }

   auto s =3D initArray!( S )( =E0=BA=95( 1, "a" ), =E0=BA=95( 2, "b" ),=
 =E0=BA=95( 3, "c" ) );

If =E0=BA=95 is too hard to type, choose another short name.

-- =

Simen

Philippe Sigaud <philippe.sigaud gmail.com> writes:

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 auto s =3D initArray!( S )( =E0=BA=95( 1, "a" ), =E0=BA=95( 2, "b" ), =E0=
=BA=95( 3, "c" ) );

 If =E0=BA=95 is too hard to type, choose another short name.


Nice looking character. Indian, hebrew?

When I want an almost non-visible char, I tend tu use _, just _.

Philippe

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=C2=A0auto s =3D initArray!( S )( =E0=BA=95( 1, "a" ), =E0=BA=95(=
 2, &quot;b&quot; ), =E0=BA=95( 3, &quot;c&quot; ) );<br><div class=3D"gmai=
l_quote"><blockquote class=3D"gmail_quote" style=3D"border-left: 1px solid =
rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">

<br>
If =E0=BA=95 is too hard to type, choose another short name.<br></blockquot=
e><div><br>Nice looking character. Indian, hebrew?<br><br>When I want an al=
most non-visible char, I tend tu use _, just _.<br><br>Philippe<br><br><br>=
=C2=A0<br>
</div></div>

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