Re: How about a Hash template?

[Denis Koroskin]

On Thu, 28 Apr 2011 03:10:15 +0400, Andrej Mitrovic  
<andrej.mitrov...@gmail.com> wrote:

I often see code written like this:
if (value == somevalue ||
   value == someothervalue ||
   value == yetanothervalue);

You could use the switch statement. But that introduces indentation,
and is rarely used for a couple of values.

I really like the "in" keyword, and I also like hashes since they can
potentially speed up look-ups compared to conventional arrays. So I
thought it would be cool to have a Hash template that constructs an
associative array which you can use especially in if statements when
you just want to know if a runtime value matches some predetermined
value.

Here's my attempt at writing it:
http://codepad.org/c4sYDSyR

Whaddya think?

Try this:


import std.stdio;

struct Set(Keys...)
{
        bool opIn_r(Key)(Key key)
        {
                // TODO: Sort!(Keys)?
                foreach (k; Keys) {
                        if (k == key) {
                                return true;
                        }
                }
                
                return false;
        }
}

Set!(Keys) set(Keys...)() {
        return Set!(Keys)();
}

void main()
{
        int needle = 42;
	bool result = needle in set!(1, 2, 3, 4, 5); // as opposed to needle == 1  
|| needle == 2 || ...
        
        writeln(result); // prints false
        
However, this only works with compile-time constants. Here is an extension  
to that (albeit probably less efficient):

        int k = 42;
        
        result = 1 in dynset(1, k, 3, 4, 5);
        writeln(result); // prints true
}

struct DynSet(Keys...)
{
        this(Keys keys)
        {
                this.keys = keys;
        }
        
        bool opIn_r(Key)(Key key)
        {
                foreach (k; keys) {
                        if (k == key) {
                                return true;
                        }
                }
                
                return false;
        }
        
        private Keys keys;
}

DynSet!(Keys) dynset(Keys...)(Keys keys) {
        return DynSet!(Keys)(keys);
}