Re: Homework help, guys!

[monarch_dodra]

On Thursday, 1 August 2013 at 23:57:47 UTC, John Colvin wrote:
On Thursday, 1 August 2013 at 23:48:33 UTC, Timon Gehr wrote:
On 08/02/2013 01:34 AM, hunt wrote:
Hello, guys. It is weird to ask about my homework here, but I 
haven't
gotten a proper answer yet. It's about D feature...maybe..
http://dpaste.dzfl.pl/905d6ad7

Question is that "Investigate how D allows you to defend your 
definition
of Map so that it may be used only with a type of key that is
comparable, and place this defense in your solution."

Please leave your comments here. Thank you so much.




This should get you started:

http://dlang.org/concepts.html
http://dlang.org/traits.html#compiles

Also, say hello to the most esoteric expression I can think of: 
D's "is" expression

http://dlang.org/expression.html#IsExpression

http://dpaste.dzfl.pl/f3d7c828

//Via constraits
//This will do a template mismatch
struct Map1(T)
if (is(typeof(T.init < T.init)))
{
    //Who cares 
}

//Via (explicit) compilation errors
struct Map2(T)
{
    static assert (is(typeof(T.init < T.init)), "Error, " ~ T ~ " 
is not comparable.");
}

void main()
{
    struct S {} //Not comparable
    assert( is(Map1!int));
    assert(!is(Map1!S));
    assert( is(Map2!int));
    assert(!is(Map2!S));
}