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digitalmars.D.learn - rvalue references template ?

reply Joshua Reusch <yoschi arkandos.de> writes:
Is it possible to create a template turning any value into a lvalue?
This would be helpful if a function expects a reference but you dont 
need the result of the change:

///decode(S)(in S str, ref size_t index);
auto c = std.utf.decode(some_string, lval!0);
Jan 02 2012
next sibling parent Timon Gehr <timon.gehr gmx.ch> writes:
On 01/02/2012 03:02 PM, Joshua Reusch wrote:

 Is it possible to create a template turning any value into a lvalue?
 This would be helpful if a function expects a reference but you dont
 need the result of the change:

 ///decode(S)(in S str, ref size_t index);
 auto c = std.utf.decode(some_string, lval!0);


Yes, but I currently cannot see a full solution that does not heap-allocate.
Jan 02 2012
prev sibling next sibling parent =?utf-8?Q?Simen_Kj=C3=A6r=C3=A5s?= <simen.kjaras gmail.com> writes:
On Mon, 02 Jan 2012 15:02:30 +0100, Joshua Reusch <yoschi arkandos.de>  
wrote:


 Is it possible to create a template turning any value into a lvalue?
 This would be helpful if a function expects a reference but you dont  
 need the result of the change:

 ///decode(S)(in S str, ref size_t index);
 auto c = std.utf.decode(some_string, lval!0);



template LRef( T, string f = __FILE__, int l = __LINE__ ) {
     static T LRef;
}

ref T lref( T, string f = __FILE__, int l = __LINE__ )( T value ) {
     LRef!( T, f, l ) = value;
     return LRef!( T, f, l );
}

unittest {
     assert( __traits( compiles, lref(0) = 3 ) );
}

This seems to work for me. 'course, there are limitations. Behind the
scenes, this creates a global variable per instantiation, and it
cannot be used more than once per line.
Jan 02 2012
prev sibling parent reply =?utf-8?Q?Simen_Kj=C3=A6r=C3=A5s?= <simen.kjaras gmail.com> writes:
On Mon, 02 Jan 2012 15:02:30 +0100, Joshua Reusch <yoschi arkandos.de>  
wrote:


 Is it possible to create a template turning any value into a lvalue?
 This would be helpful if a function expects a reference but you dont  
 need the result of the change:

 ///decode(S)(in S str, ref size_t index);
 auto c = std.utf.decode(some_string, lval!0);



template LRef( T, string f = __FILE__, int l = __LINE__ ) {
     static T LRef;
}

ref T lref( T, string f = __FILE__, int l = __LINE__ )( T value ) {
     LRef!( T, f, l ) = value;
     return LRef!( T, f, l );
}

unittest {
     assert( __traits( compiles, lref(0) = 3 ) );
}

This seems to work for me. 'course, there are limitations. Behind the
scenes, this creates a global variable per instantiation, and it
cannot be used more than once per line.
Jan 02 2012
parent Joshua Reusch <yoschi arkandos.de> writes:
Am 02.01.2012 22:13, schrieb Simen Kjærås:

 On Mon, 02 Jan 2012 15:02:30 +0100, Joshua Reusch <yoschi arkandos.de>
 wrote:


 Is it possible to create a template turning any value into a lvalue?
 This would be helpful if a function expects a reference but you dont
 need the result of the change:

 ///decode(S)(in S str, ref size_t index);
 auto c = std.utf.decode(some_string, lval!0);



 template LRef( T, string f = __FILE__, int l = __LINE__ ) {
 static T LRef;
 }

 ref T lref( T, string f = __FILE__, int l = __LINE__ )( T value ) {
 LRef!( T, f, l ) = value;
 return LRef!( T, f, l );
 }

 unittest {
 assert( __traits( compiles, lref(0) = 3 ) );
 }

 This seems to work for me. 'course, there are limitations. Behind the
 scenes, this creates a global variable per instantiation, and it
 cannot be used more than once per line.


I tried something similar, but always got some compiler errors... I 
think I tried to change a compile-time value. But your function works !

Thank you !
Jan 02 2012