I spoke too soon.
class AA(Key, Data) if (isNumeric (Key) )
didn't work with a larger case,
s$ dmd aa.d
/usr/include/d/dmd/phobos/std/traits.d(2576): Error: template
std.traits.isNumeric(T) is not a function template
aa.d(200): Error: template std.traits.isNumeric(T) cannot deduce
template function from argument types !()(int)
aa.d(494): Error: template instance AA!(int,string) does not match
template declaration AA(Key,Data) if (isNumeric(Key))
aa.d(494): Error: AA!(int,string) is used as a type
though
class AA (Key, Data) if (is (Key : long))
did work. Or at least it compiled without error.
On 09/24/2011 05:05 PM, Charles Hixson wrote:
On 09/24/2011 05:05 PM, Charles Hixson wrote:
On 09/24/2011 04:31 PM, Jonathan M Davis wrote:
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
You're right. std.traits is where I should be looking.
On 09/24/2011 04:31 PM, Jonathan M Davis wrote:
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
You're right. std.traits is where I should be looking.
