www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - D 2.x invariant question

reply Charles D Hixson <charleshixsn earthlink.net> writes:
Would the following function:
invariant Body	opIndex	(Key k)
{  if (k in _cache)
    { ....
       return  _cache[k].bdy;
    }
    return  null;
}

return values that were invariant, or would that type have to 
be declared at the declaration of the type "Body"?
Oct 31 2007
parent reply "Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:
"Charles D Hixson" <charleshixsn earthlink.net> wrote in message 
news:fgao71$21fp$1 digitalmars.com...

 Would the following function:
 invariant Body opIndex (Key k)
 {  if (k in _cache)
    { ....
       return  _cache[k].bdy;
    }
    return  null;
 }

 return values that were invariant, or would that type have to be declared 
 at the declaration of the type "Body"?



I think this makes the method opIndex invariant, which means this function 
can only access invariant members, or something.  If you want an 
invariant(Body), use... invariant(Body) as the return type.

Aside: performance increase, you can avoid the double lookup:

if(auto val = k in cache)
{
    ..use val here..
    return val.bdy;
}

'in' returns a pointer to the value, and you can declare and assign a 
variable in the condition of an 'if' statement.
Oct 31 2007
parent Charles D Hixson <charleshixsn earthlink.net> writes:
Jarrett Billingsley wrote:

 "Charles D Hixson" <charleshixsn earthlink.net> wrote in message 
 news:fgao71$21fp$1 digitalmars.com...

 Would the following function:
 invariant Body opIndex (Key k)
 {  if (k in _cache)
    { ....
       return  _cache[k].bdy;
    }
    return  null;
 }

 return values that were invariant, or would that type have to be declared 
 at the declaration of the type "Body"?



 I think this makes the method opIndex invariant, which means this function 
 can only access invariant members, or something.  If you want an 
 invariant(Body), use... invariant(Body) as the return type.
 
 Aside: performance increase, you can avoid the double lookup:
 
 if(auto val = k in cache)
 {
     ..use val here..
     return val.bdy;
 }
 
 'in' returns a pointer to the value, and you can declare and assign a 
 variable in the condition of an 'if' statement. 
 
 



(I *kenw* that about "in", but I keep forgetting.)
Oct 31 2007