Re: how to instantiate explicitly template parameters in struct A(T1){this(T2)(){...}}
On Tue, 14 May 2013 00:32:49 -0400, Timothee Cour
wrote:
I declared fun(T) as fun(T)() with the added parenthesis, and it
worked (tested on dmd 2.062 / ubuntu 64bits).
sorry I reduced wrongly.
Here's the inconsistency:
struct A {
this(T)(T x) { }
}
auto fun1(){
auto a=A.__ctor!(int)(1); //OK
This line causes an error message for me:
testctor.d(5): Error: need 'this' for 'this' of type 'pure nothrow ref
@safe A(int x)'
return a;
}
auto fun2(){
// return A.__ctor!(int)(1); //uncomment gives Error: type A is not an
expression
Same error for me here:
testctor.d(9): Error: need 'this' for 'this' of type 'pure nothrow ref
@safe A(int x)'
I'm using dmd beta candidate, 2.061 does give the same error message you
have.
Note that you may expect this as you are using an undocumented "feature" :)
-Steve
Re: how to instantiate explicitly template parameters in struct A(T1){this(T2)(){...}}
> __ctor is a 'this' call, it needs a this (BTW, I get different errors than > you): Seems like not (see my corrected bug in previous post) > Not sure how you would do that in one line ditto >> Why not use 'this' instead of '__ctor', and make it documented (and >> reliable, ie work in the above case) ? >> I don't see how that could create ambiguity, and that would solve the >> problem raised in this thread. > > > You could do that. It may have some ambiguous syntax implications. I really can't think of any, and I think it would just make sense, given that it'd match the way the function is declared.
Re: how to instantiate explicitly template parameters in struct A(T1){this(T2)(){...}}
> I declared fun(T) as fun(T)() with the added parenthesis, and it
> worked (tested on dmd 2.062 / ubuntu 64bits).
sorry I reduced wrongly.
Here's the inconsistency:
struct A {
this(T)(T x) { }
}
auto fun1(){
auto a=A.__ctor!(int)(1); //OK
return a;
}
auto fun2(){
// return A.__ctor!(int)(1); //uncomment gives Error: type A is not an
expression
}
void main(){
}
Re: how to instantiate explicitly template parameters in struct A(T1){this(T2)(){...}}
On Tuesday, 14 May 2013 at 03:34:52 UTC, Timothee Cour wrote:
A)
The behavior of __ctor (whether or not documented) seems broken
/ unreliable:
struct A{this(T)(T x){}}
void fun(T){
auto a=A.__ctor!(int)(1);
}
void main(){
auto a=A.__ctor!(int)(1); //ok
fun!int(); //Error: type A is not an expression
}
Is that a bug?
B)
Why not use 'this' instead of '__ctor', and make it documented
(and
reliable, ie work in the above case) ?
I don't see how that could create ambiguity, and that would
solve the
problem raised in this thread.
I declared fun(T) as fun(T)() with the added parenthesis, and it
worked (tested on dmd 2.062 / ubuntu 64bits).
The following prints "it works" twice:
import std.stdio;
struct A {
this(T)(T x) {
writeln("it works");
}
}
void fun(T)(){
auto a=A.__ctor!(int)(1);
}
void main(){
auto a=A.__ctor!(int)(1); //ok
fun!int(); //ok too
}
--jm
Re: how to instantiate explicitly template parameters in struct A(T1){this(T2)(){...}}
On Mon, 13 May 2013 23:34:39 -0400, Timothee Cour
wrote:
A)
The behavior of __ctor (whether or not documented) seems broken /
unreliable:
struct A{this(T)(T x){}}
void fun(T){
auto a=A.__ctor!(int)(1);
}
void main(){
auto a=A.__ctor!(int)(1); //ok
fun!int(); //Error: type A is not an expression
}
__ctor is a 'this' call, it needs a this (BTW, I get different errors than
you):
struct A{this(T)(T x){}}
void fun(T)(){
A a;
a.__ctor!(int)(1);
}
void main(){
A a;
a.__ctor!(int)(1);
fun!int();
}
Not sure how you would do that in one line (and I assume you had a typo in
fun(T) since it wasn't valid syntax).
B)
Why not use 'this' instead of '__ctor', and make it documented (and
reliable, ie work in the above case) ?
I don't see how that could create ambiguity, and that would solve the
problem raised in this thread.
You could do that. It may have some ambiguous syntax implications.
-Steve
Re: how to instantiate explicitly template parameters in struct A(T1){this(T2)(){...}}
A)
The behavior of __ctor (whether or not documented) seems broken / unreliable:
struct A{this(T)(T x){}}
void fun(T){
auto a=A.__ctor!(int)(1);
}
void main(){
auto a=A.__ctor!(int)(1); //ok
fun!int(); //Error: type A is not an expression
}
Is that a bug?
B)
Why not use 'this' instead of '__ctor', and make it documented (and
reliable, ie work in the above case) ?
I don't see how that could create ambiguity, and that would solve the
problem raised in this thread.
Re: how to instantiate explicitly template parameters in struct A(T1){this(T2)(){...}}
On 05/13/2013 10:27 PM, Timothee Cour wrote:
While writing DIP40, I came upon the following question:
how to instantiate explicitly template parameters for both the
class/struct AND the constructor?
for example: struct A(T1){this(T2)(){...}} ? (T2 could be used
somehow inside the ctor body for example)
// auto a=A!double!int(); // CT error
The example is a bit contrived but there could be less contrived ones
where both A and ctor need explicit instantiations.
There is a more basic question:
How to explicitly pass template arguments to _any_ constructor?
Re: how to instantiate explicitly template parameters in struct A(T1){this(T2)(){...}}
On 05/14/2013 01:25 AM, Timon Gehr wrote:
On 05/13/2013 10:27 PM, Timothee Cour wrote:
While writing DIP40, I came upon the following question:
how to instantiate explicitly template parameters for both the
class/struct AND the constructor?
for example: struct A(T1){this(T2)(){...}} ? (T2 could be used
somehow inside the ctor body for example)
// auto a=A!double!int(); // CT error
The example is a bit contrived but there could be less contrived ones
where both A and ctor need explicit instantiations.
There is a more basic question:
How to explicitly pass template arguments to _any_ constructor?
(There currently is no documented way.)
Re: how to instantiate explicitly template parameters in struct A(T1){this(T2)(){...}}
On Mon, 13 May 2013 19:04:39 -0400, Timothee Cour wrote: Thanks! should that be considered as a limitation, and therefore be fixed? (for example by documenting the __ctor syntax)? The static make trick is boilerplate and shouldn't be considered the best way. Well, it's not really boilerplate :) It takes the place of an actual constructor. In other words, you don't also need a this() function. Technically, what we are missing is the name of the constructor. Otherwise, you have nothing to apply the '!' to. As I said, I don't know if __ctor is official, maybe it is already. I know some code in druntime uses it. -Steve
Re: how to instantiate explicitly template parameters in struct A(T1){this(T2)(){...}}
Thanks!
should that be considered as a limitation, and therefore be fixed?
(for example by documenting the __ctor syntax)?
The static make trick is boilerplate and shouldn't be considered the best way.
On Mon, May 13, 2013 at 3:06 PM, Steven Schveighoffer
wrote:
> On Mon, 13 May 2013 16:27:44 -0400, Timothee Cour
> wrote:
>
>> While writing DIP40, I came upon the following question:
>> how to instantiate explicitly template parameters for both the
>> class/struct AND the constructor?
>> for example: struct A(T1){this(T2)(){...}} ? (T2 could be used
>> somehow inside the ctor body for example)
>> // auto a=A!double!int(); // CT error
>> The example is a bit contrived but there could be less contrived ones
>> where both A and ctor need explicit instantiations.
>
>
> Since you can't call the ctor directly [1], this isn't possible in any case,
> even without a templated struct.
>
> What you CAN do is specify a constructing function:
>
> struct A(T1) {
> static A make(T2)(){...}
> }
>
> auto a = A!double.make!int();
>
> -Steve
>
> ==
> [1] This does work, but is not documented/official AFAIK:
>
> struct S
> {
> this(T)(int i) {}
> }
> void main()
> {
> S s;
> s.__ctor!double(1);
> }
Re: how to instantiate explicitly template parameters in struct A(T1){this(T2)(){...}}
On Mon, 13 May 2013 16:27:44 -0400, Timothee Cour
wrote:
While writing DIP40, I came upon the following question:
how to instantiate explicitly template parameters for both the
class/struct AND the constructor?
for example: struct A(T1){this(T2)(){...}} ? (T2 could be used
somehow inside the ctor body for example)
// auto a=A!double!int(); // CT error
The example is a bit contrived but there could be less contrived ones
where both A and ctor need explicit instantiations.
Since you can't call the ctor directly [1], this isn't possible in any
case, even without a templated struct.
What you CAN do is specify a constructing function:
struct A(T1) {
static A make(T2)(){...}
}
auto a = A!double.make!int();
-Steve
==
[1] This does work, but is not documented/official AFAIK:
struct S
{
this(T)(int i) {}
}
void main()
{
S s;
s.__ctor!double(1);
}
Re: how to instantiate explicitly template parameters in struct A(T1){this(T2)(){...}}
On Monday, May 13, 2013 13:27:44 Timothee Cour wrote:
> While writing DIP40, I came upon the following question:
> how to instantiate explicitly template parameters for both the
> class/struct AND the constructor?
> for example: struct A(T1){this(T2)(){...}} ? (T2 could be used
> somehow inside the ctor body for example)
> // auto a=A!double!int(); // CT error
> The example is a bit contrived but there could be less contrived ones
> where both A and ctor need explicit instantiations.
I don't believe that you can _ever_ give explicit template arguments to a
constructor whether the type is templated or not. Note that this code doesn't
compile:
struct S
{
this(T)(T val)
{
}
}
void main()
{
auto s = S!float(5);
}
and gives this error:
q.d(10): Error: template instance S!(float) S is not a template declaration, it
is a struct
q.d(10): Error: template instance S!(float) S is not a template declaration, it
is a struct
- Jonathan M Davis
