Introduction to traits (and __traits)

[Ali Çehreli]

On 08/30/2013 01:57 PM, Joseph Rushton Wakeling wrote:
> On 30/08/13 21:40, Benjamin Thaut wrote:
>> You need to put it into a static if, otherwise the compiler will continue
>> semantic checks on the second part of the expression. E.g.
>>
>> template isGraph(G)
>> {
>>    static if(__traits(hasMember, G, "directed"))
>>      enum bool isGraph = isBoolean!(typeof(G.directed));
>>    else
>>      enum bool isGraph = false;
>> }
>
> Ahh, right, thanks. :-)
>
> Is there a recommended way for handling the case where there are many
> such members -- say about 10 or more?  The static if's could become very
> highly nested with this approach.  I suppose I could go through like this:
>
>      static if(!__traits(hasMember, G, "one"))
>          enum bool isGraph = false;
>      else static if(!__traits(hasMember, G, "two"))
>          enum bool isGraph = false;
>      else static if ...
>          ...
>      else
>      {
>          // Now I know all the members exist and I can
>          // start checking out their properties ...
>      }
>

How about allSatisfy:

   http://dlang.org/phobos/std_typetuple.html#.allSatisfy

Ali