On 02/17/2012 05:59 PM, Timon Gehr wrote:
> On 02/18/2012 12:04 AM, Ali Çehreli wrote:
>> On 02/17/2012 09:08 AM, Steven Schveighoffer wrote:
>>
>> > What you are asking for is IFTI (Implicit Function Template
>> > Instantiation) on constructors, and is perfectly possible, but not
>> > implemented:
>> >
>> > http://d.puremagic.com/issues/show_bug.cgi?id=6082
>>
>> What was the resolution for the case when the constructor is a template?
>> I think that's why IFTI doesn't work for structs and classes in C++.
>> Although, I can't get the following to compile in D anyway (that old and
>> annoying error message again! :p):
>>
>> Error: no property 'opCall' for type 'deneme.B'
>>
>> import std.conv;
>>
>> class B
>> {
>> string s;
>>
>> this(T)(T t) // <-- Is the struct a template
>> // or the constructor a template?
>
> The constructor it is, and B is a class, not a struct.
Ah! Thanks!
So today the following works; and not B, but the constructor is a template:
import std.conv;
struct B
{
string s;
this(T)(T t) // <-- constructor is a template
{
s = to!string(t);
}
}
void main()
{
auto b0 = B(42); // construct with int
assert(b0.s == "42");
auto b1 = B(1.5); // construct with double
assert(b1.s == "1.5");
}
With the proposed feature, the struct would be a template.
>> {
>> s = to!string(t);
>> }
>> }
>>
>> void main()
>> {
>> auto b0 = B(42);
>> }
>>
>> I wasn't around when the static opCall() was designed but it is probably
>> the very first thing that bugged me about D. :) I want B(42) to be
>> object construction, not opCall(), which is not even defined.
>>
>> Ali
>>
>
> Why? What useful semantics would that have for classes?
I am not sure but the point is, if function templates provide IFTI, then
because of being functions the constructors could provide IFTI as well,
as it does for the struct B above.
As an aside, I don't know why it is not the same with classes. I hope I
am not again making an error in the following code. I have replaced
'struct' with 'class' and inserted two 'new' keywords:
import std.conv;
class B
{
string s;
this(T)(T t)
{
s = to!string(t);
}
}
void main()
{
auto b0 = new B(42); // line 61459
assert(b0.s == "42");
auto b1 = new B(1.5); // line 61462
assert(b1.s == "1.5");
}
The compiler says:
deneme.d(61459): Error: no constructor for B
deneme.d(61462): Error: no constructor for B
deneme.d(61462): Warning: statement is not reachable
Ali
