• Paolo Invernizzi (11/11) Jun 15 2013 Hi all,
• =?UTF-8?B?QWxpIMOHZWhyZWxp?= (24/35) Jun 15 2013 I don't know whether it works correctly, but can you try calling

"Paolo Invernizzi" <arathorn fastwebnet.it> writes:

Hi all,

How to implement a proper hash method for a struct/class having 
as a base one or more floating point?

When I compile with the -w flags, dmd 2.063 tells me that the 
function must be size_t toHash() const nothrow  safe.

The point is that the nothrow doesn't permit the std.conv.to 
conversions, while the  safe does not permit the cast().

So how to perform a little math on the floating and then turning 
the result to a proper integer hash?

Suggestions welcome! Thank!

Paolo Invernizzi

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 06/15/2013 03:13 AM, Paolo Invernizzi wrote:
 Hi all,

 How to implement a proper hash method for a struct/class having as a
 base one or more floating point?

 When I compile with the -w flags, dmd 2.063 tells me that the function
 must be size_t toHash() const nothrow  safe.

 The point is that the nothrow doesn't permit the std.conv.to
 conversions, while the  safe does not permit the cast().

 So how to perform a little math on the floating and then turning the
 result to a proper integer hash?

 Suggestions welcome! Thank!

 Paolo Invernizzi

I don't know whether it works correctly, but can you try calling 
typeid(f).getHash(&f):

import std.stdio;

struct S
{
     float f;
     int i;

     const hash_t toHash() nothrow  safe
     {
         return typeid(f).getHash(&f);
     }
}

void main()
{
     string[S] aa = [ S(0.5) : "half", S(0.25) : "quarter" ];

     aa[S(0.5)] = "one over two";
     aa[S(0.25)] = "one over four";

     writeln(aa);
}

Of course I have used exactly representable values 0.5 and 0.25 instead 
of any other float value. Maybe you can afford to store such a value (in 
addition to your actual float value) to be used for hashing.

Ali