class specialization for integral types

[Jonathan M Davis]

On Saturday, September 24, 2011 16:14:48 Charles Hixson wrote:
> On 09/24/2011 02:33 PM, Jonathan M Davis wrote:
> > On Saturday, September 24, 2011 14:16:12 Charles Hixson wrote:
> >> How would a specialize a parameterized class to only allow integral
> >> parameters (i.e., anything that would respond "true" to
> >> static if (is (T : long) )
> >> 
> >> (I'd have said "static if (is (T : cent) )" or "static if (is (T :
> >> ucent) )", but those are still marked "reserved for future use".)
> >> 
> >> I do want to allow byte, ubyte, etc. to be legal values.
> > 
> > Parameterized? As in templated? Just use a template constraint.
> > 
> > class C(T)
> > 
> >      if(is(T : long))
> > 
> > {
> > }
> > 
> > T will then be allowed to be anything which is implicitly convertible to
> > long. I'd suggest using std.traits.isIntegral instead though.
> > 
> > class C(T)
> > 
> >      if(isIntegral!T)
> > 
> > {
> > }
> > 
> > It specifically tests for whether the type is a byte, ubyte, short,
> > ushort, int, uint, long, or ulong, so it won't included stray structs
> > or classes which would be implicitly convertible to long, and if/when
> > eont and ucent come along, they'd be added to isIntegral and be
> > automatically supported.
> > 
> > - Jonathan M Davis
> 
> Thanks.  isIntegral has given me some error messages that I couldn't
> understand, though, so I'll take your first suggestion.
> 
> This is actually a rephrase of the question I first sent, when somehow
> didn't appear on the list:
> 
> When checking a template variable, what are the base cases for is?
> long will satisfy all integer types.  I.e.
>    is (typeof(tst0) : long)  == true
> real will satisfy all floating point types.
> I think that string will satisfy all arrays of characters (need to check
> that).
> 
> But there are lots of other kinds of array.  And while Object will
> satisfy all classes, I don't know anything analogous for structs.  Then
> there's enums (would they be caught by their base type as above, or with
> they be like string and require an immutable corresponding to the base type?
> 
> I'd like to create a chunk of code that will handle all possible types
> (for a particular operation) but how to do this isn't obvious.  I can
> handle most common types, but there seem to be LOTS of less frequent types.

You really should look at std.traits. It has that sort of stuff in it. It's 
what you should be using for really general stuff. Unqual, isDynamicArray, 
isFloatingPoint, etc. are all the sorts of things that you should be using for 
general tests on types.

is(T == U) is going to be true if T and U are exactly the same type.

is(T : U) is going to be true if T is implicitly convertible to U.

If all that you care about is class or struct, then you can use

is(T == class)
is(T == struct)

You should also look at http://www.d-programming-language.org/traits.html.

- Jonathan M Davis