Re: Erroneous "auto can only be used for template function parameters"?
On Saturday, 20 June 2015 at 01:50:11 UTC, Yuxuan Shui wrote:
Try to compile this code snippet:
import std.traits;
template a(R) {
auto a(S)(auto ref R i) {
return cast(S)i*2;
}
}
template ReturnTypeEx(alias A, B) {
alias ReturnTypeEx = ReturnType!(A!B);
}
template b(alias R) {
int b(S)(S i) {
alias Ra = ReturnTypeEx!(R, S);
return cast(int)R!S(i);
}
}
void main() {
alias bb = b!(a!ulong);
pragma(msg, ReturnTypeEx!(bb, int));
}
DMD reports:
sadf.d(3): Error: auto can only be used for template function
parameters
sadf.d(8): Error: template instance sadf.a!ulong.A!int error
instantiating
sadf.d(12):instantiated from here: ReturnTypeEx!(a, int)
sadf.d(8):instantiated from here: A!int
sadf.d(18):instantiated from here: ReturnTypeEx!(b, int)
sadf.d(18):while evaluating pragma(msg,
ReturnTypeEx!(b, int))
But a(S)(auto ref R) is indeed a template function, so I don't
understand.
Another thing I discovered is instantiation like this: (a!T)!S
will result in "C style cast illegal", which is clearly wrong
because this is not a cast, (a!T) is not necessarily a type.
Erroneous "auto can only be used for template function parameters"?
Try to compile this code snippet:
import std.traits;
template a(R) {
auto a(S)(auto ref R i) {
return cast(S)i*2;
}
}
template ReturnTypeEx(alias A, B) {
alias ReturnTypeEx = ReturnType!(A!B);
}
template b(alias R) {
int b(S)(S i) {
alias Ra = ReturnTypeEx!(R, S);
return cast(int)R!S(i);
}
}
void main() {
alias bb = b!(a!ulong);
pragma(msg, ReturnTypeEx!(bb, int));
}
DMD reports:
sadf.d(3): Error: auto can only be used for template function
parameters
sadf.d(8): Error: template instance sadf.a!ulong.A!int error
instantiating
sadf.d(12):instantiated from here: ReturnTypeEx!(a, int)
sadf.d(8):instantiated from here: A!int
sadf.d(18):instantiated from here: ReturnTypeEx!(b, int)
sadf.d(18):while evaluating pragma(msg, ReturnTypeEx!(b,
int))
But a(S)(auto ref R) is indeed a template function, so I don't
understand.
Re: OT - civility in a professional environment
nice read, thank you
Re: best way to interface D code to Excel
On Wednesday, 17 June 2015 at 18:35:36 UTC, Laeeth Isharc wrote: Hi. I know D has support for COM - not sure of its status. And there was a Microsoft chap who posted here a couple of years back - wonderful templated code that made it easy to write this kind of thing. Unfortunately he wasn't able to share it publicly. Laeeth. I haven't ever done any real work with it, and certainly nothing with Excel. But Juno provides similarities for COM to what the Microsoft guy demonstrated. I made some changes so it would compile in dmd 2.070, didn't test though so it is still it's own branch. https://github.com/JesseKPhillips/Juno-Windows-Class-Library/tree/dmd6.070
OT - civility in a professional environment
http://www.nytimes.com/2015/06/21/opinion/sunday/is-your-boss-mean.html?_r=0 Off topic, but perhaps of interest. Laeeth.
Re: Return types of the methods of a struct
On 6/19/15 12:09 PM, Quentin Ladeveze wrote:
On Friday, 19 June 2015 at 14:42:59 UTC, Steven Schveighoffer wrote:
On 6/19/15 10:13 AM, Quentin Ladeveze wrote:
On Friday, 19 June 2015 at 14:04:05 UTC, Daniel Kozák wrote:
On Fri, 19 Jun 2015 13:52:52 +
Quentin Ladeveze via Digitalmars-d-learn
wrote:
On Friday, 19 June 2015 at 13:38:45 UTC, Steven Schveighoffer wrote:
>
> Does this work for you, or is there a further expectation?
>
> auto asTuple() { return Tuple!(int, "a", ...)(a, b, > >
stringValue);}
>
> -Steve
In fact, I was trying to use traits to create the tuple
automatically and being able to add or remove methods to the
struct without breaking the asTuple method.
I used allMembers for the name of the methods, but I didn't found
anything for their return types or their values.
Thank you.
http://dlang.org/phobos/std_traits.html#ReturnType
http://dlang.org/phobos/std_traits.html#ParameterTypeTuple
These are interesting and can be useful, but allMembers returns strings
and not functions, so I can't apply ReturnType.
It's a *compile time* string. D is able to do some amazing things with
this :)
// assuming 'a' is the first member
mixin("alias aReturnType = ReturnType!(Example." ~
__traits(allMembers, Example)[0] ~ ");");
static assert(is(aReturnType == int));
Using foreach over allMembers, you can construct a perfect return
tuple using introspection and mixin.
-Steve
I would never have thought about mixins, this is amazing ! But thinking
at compile time still is a little difficult for me, and now I don't
understand how you can construct your tuple. I've been trying to create
a string, by iterating on allMembers and concatenating the result of my
functions in a string. But of course, I cannot use this string at
compile time.
Now I know there is a way t do it, but my brain just can't figure it out.
Can you help me ?
The string must stay compile time. This means it must be calculated:
1. in a mixin statement
Example is what I wrote earlier.
2. as an initializer to an immutable, enum, or non-local variable
enum x = "Blah." ~ __traits(allMembers, Blah)[0]; // x is compile-time
3. inside a CTFE function. A CTFE function is just a normal runtime
function with restrictions (see
http://dlang.org/function.html#interpretation). But you must *call* it
from a context like 1 or 2:
string foo(string a, string b) { return a ~ b; } // foo is CTFEable
auto x1 = foo("a", "b"); // x1 is a runtime string, foo is called at runtime
enum x2 = foo("a", "b"); // x2 is a compile-time string, foo is executed
at compile time (it is not called during execution of your program
mixin("int " ~ x1 ~ ";"); // error, can't use runtime string x1
mixin("int " ~ x2 ~ ";"); // ok, declares int ab;
mixin("int " ~ foo("c", "d") ~ ";"); // ok, declares int ab;
Keep your code all executing at compile time, and you can use your
strings to write your code for you!
-Steve
Re: Are stack+heap classes possible in D?
On Friday, 19 June 2015 at 19:10:11 UTC, Shachar Shemesh wrote: On 14/06/15 04:31, Adam D. Ruppe wrote: On Sunday, 14 June 2015 at 00:52:20 UTC, FujiBar wrote: I have read that in D structs are always allocated on the stack while classes are always allocated on the heap. That's not true; it is a really common misconception. Putting a struct on the heap is trivial and built into the language: `S* s = new S();` Well Yeah. You would get a reference to a struct. The struct will be on the heap. In that narrow sense, you are right that it is possible. However, this does not behave like a normal struct. In particular, when will the destructor be called? (answer: never, not even before the memory is collected). So, no, I think D experts should avoid telling newbies it is okay to just "new struct foo".[1] Shachar 1 - The counter argument is, of course, that struct destructors should not be counted upon to do anything useful anyways, as they are far from guaranteed to run even in situations where one would expect them to. This just relates to another area where D skirts truth in advertising when people say that D supports RAII. the destructor bug has been fixed for a while. for your second point, the issue is that D doesn't separate destructors from finalizers and it feels like it was designed by someone with little knowledge in low level memory management honestly.
Re: Are stack+heap classes possible in D?
On 14/06/15 04:31, Adam D. Ruppe wrote: On Sunday, 14 June 2015 at 00:52:20 UTC, FujiBar wrote: I have read that in D structs are always allocated on the stack while classes are always allocated on the heap. That's not true; it is a really common misconception. Putting a struct on the heap is trivial and built into the language: `S* s = new S();` Well Yeah. You would get a reference to a struct. The struct will be on the heap. In that narrow sense, you are right that it is possible. However, this does not behave like a normal struct. In particular, when will the destructor be called? (answer: never, not even before the memory is collected). So, no, I think D experts should avoid telling newbies it is okay to just "new struct foo".[1] Shachar 1 - The counter argument is, of course, that struct destructors should not be counted upon to do anything useful anyways, as they are far from guaranteed to run even in situations where one would expect them to. This just relates to another area where D skirts truth in advertising when people say that D supports RAII.
Re: Return types of the methods of a struct
On Friday, 19 June 2015 at 15:47:09 UTC, ZombineDev wrote: On Friday, 19 June 2015 at 14:13:46 UTC, Quentin Ladeveze wrote: [..] These are interesting and can be useful, but allMembers returns strings and not functions, so I can't apply ReturnType. Here's my solution: http://dpaste.dzfl.pl/c69de3c16d75 Thank you very much, this solution is interesting too.
Re: Return types of the methods of a struct
On Friday, 19 June 2015 at 15:36:54 UTC, Justin Whear wrote: On Fri, 19 Jun 2015 13:27:13 +, Quentin Ladeveze wrote: Is there any way to have a asTuple method in this struct that would returns something like : Tuple!(int, "a", float, "b", string, "c") and that will contain the values of the methods of the struct ? Thanks. You'll want to work your way through this example carefully as it's basically template-based functional programming, but I think does what you want: http://dpaste.dzfl.pl/b048ea3adb93 This is interesting, thank you very much ! I will try to figure out how it works now
Re: Return types of the methods of a struct
On Friday, 19 June 2015 at 14:42:59 UTC, Steven Schveighoffer
wrote:
On 6/19/15 10:13 AM, Quentin Ladeveze wrote:
On Friday, 19 June 2015 at 14:04:05 UTC, Daniel Kozák wrote:
On Fri, 19 Jun 2015 13:52:52 +
Quentin Ladeveze via Digitalmars-d-learn
wrote:
On Friday, 19 June 2015 at 13:38:45 UTC, Steven
Schveighoffer wrote:
>
> Does this work for you, or is there a further expectation?
>
> auto asTuple() { return Tuple!(int, "a", ...)(a, b, >
> stringValue);}
>
> -Steve
In fact, I was trying to use traits to create the tuple
automatically and being able to add or remove methods to the
struct without breaking the asTuple method.
I used allMembers for the name of the methods, but I didn't
found
anything for their return types or their values.
Thank you.
http://dlang.org/phobos/std_traits.html#ReturnType
http://dlang.org/phobos/std_traits.html#ParameterTypeTuple
These are interesting and can be useful, but allMembers
returns strings
and not functions, so I can't apply ReturnType.
It's a *compile time* string. D is able to do some amazing
things with this :)
// assuming 'a' is the first member
mixin("alias aReturnType = ReturnType!(Example." ~
__traits(allMembers, Example)[0] ~ ");");
static assert(is(aReturnType == int));
Using foreach over allMembers, you can construct a perfect
return tuple using introspection and mixin.
-Steve
I would never have thought about mixins, this is amazing ! But
thinking at compile time still is a little difficult for me, and
now I don't understand how you can construct your tuple. I've
been trying to create a string, by iterating on allMembers and
concatenating the result of my functions in a string. But of
course, I cannot use this string at compile time.
Now I know there is a way t do it, but my brain just can't figure
it out.
Can you help me ?
Re: Return types of the methods of a struct
On Friday, 19 June 2015 at 14:13:46 UTC, Quentin Ladeveze wrote: [..] These are interesting and can be useful, but allMembers returns strings and not functions, so I can't apply ReturnType. Here's my solution: http://dpaste.dzfl.pl/c69de3c16d75
Re: Return types of the methods of a struct
On Fri, 19 Jun 2015 13:27:13 +, Quentin Ladeveze wrote: > > Is there any way to have a asTuple method in this struct that would > returns something like : > > Tuple!(int, "a", float, "b", string, "c") > > and that will contain the values of the methods of the struct ? > > Thanks. You'll want to work your way through this example carefully as it's basically template-based functional programming, but I think does what you want: http://dpaste.dzfl.pl/b048ea3adb93
Re: Return types of the methods of a struct
On 6/19/15 10:13 AM, Quentin Ladeveze wrote:
On Friday, 19 June 2015 at 14:04:05 UTC, Daniel Kozák wrote:
On Fri, 19 Jun 2015 13:52:52 +
Quentin Ladeveze via Digitalmars-d-learn
wrote:
On Friday, 19 June 2015 at 13:38:45 UTC, Steven Schveighoffer wrote:
>
> Does this work for you, or is there a further expectation?
>
> auto asTuple() { return Tuple!(int, "a", ...)(a, b, > stringValue);}
>
> -Steve
In fact, I was trying to use traits to create the tuple
automatically and being able to add or remove methods to the
struct without breaking the asTuple method.
I used allMembers for the name of the methods, but I didn't found
anything for their return types or their values.
Thank you.
http://dlang.org/phobos/std_traits.html#ReturnType
http://dlang.org/phobos/std_traits.html#ParameterTypeTuple
These are interesting and can be useful, but allMembers returns strings
and not functions, so I can't apply ReturnType.
It's a *compile time* string. D is able to do some amazing things with
this :)
// assuming 'a' is the first member
mixin("alias aReturnType = ReturnType!(Example." ~ __traits(allMembers,
Example)[0] ~ ");");
static assert(is(aReturnType == int));
Using foreach over allMembers, you can construct a perfect return tuple
using introspection and mixin.
-Steve
Re: Return types of the methods of a struct
On 6/19/15 10:01 AM, Baz wrote:
On Friday, 19 June 2015 at 13:52:54 UTC, Quentin Ladeveze wrote:
On Friday, 19 June 2015 at 13:38:45 UTC, Steven Schveighoffer wrote:
Does this work for you, or is there a further expectation?
auto asTuple() { return Tuple!(int, "a", ...)(a, b, stringValue);}
-Steve
In fact, I was trying to use traits to create the tuple automatically
and being able to add or remove methods to the struct without breaking
the asTuple method.
I used allMembers for the name of the methods, but I didn't found
anything for their return types or their values.
Thank you.
when the return type is defined inside the function it's called a
'Voldemort type',
see http://www.drdobbs.com/cpp/voldemort-types-in-d/232901591?pgno=2
Actually, this isn't a voldemort type, because the type can be named
outside the function.
-Steve
Re: Return types of the methods of a struct
On Friday, 19 June 2015 at 14:04:05 UTC, Daniel Kozák wrote:
On Fri, 19 Jun 2015 13:52:52 +
Quentin Ladeveze via Digitalmars-d-learn
wrote:
On Friday, 19 June 2015 at 13:38:45 UTC, Steven Schveighoffer
wrote:
>
> Does this work for you, or is there a further expectation?
>
> auto asTuple() { return Tuple!(int, "a", ...)(a, b,
> stringValue);}
>
> -Steve
In fact, I was trying to use traits to create the tuple
automatically and being able to add or remove methods to the
struct without breaking the asTuple method.
I used allMembers for the name of the methods, but I didn't
found
anything for their return types or their values.
Thank you.
http://dlang.org/phobos/std_traits.html#ReturnType
http://dlang.org/phobos/std_traits.html#ParameterTypeTuple
These are interesting and can be useful, but allMembers returns
strings and not functions, so I can't apply ReturnType.
Re: Return types of the methods of a struct
On Friday, 19 June 2015 at 13:52:54 UTC, Quentin Ladeveze wrote:
On Friday, 19 June 2015 at 13:38:45 UTC, Steven Schveighoffer
wrote:
Does this work for you, or is there a further expectation?
auto asTuple() { return Tuple!(int, "a", ...)(a, b,
stringValue);}
-Steve
In fact, I was trying to use traits to create the tuple
automatically and being able to add or remove methods to the
struct without breaking the asTuple method.
I used allMembers for the name of the methods, but I didn't
found anything for their return types or their values.
Thank you.
when the return type is defined inside the function it's called a
'Voldemort type',
see
http://www.drdobbs.com/cpp/voldemort-types-in-d/232901591?pgno=2
Re: Return types of the methods of a struct
On Fri, 19 Jun 2015 13:52:52 +
Quentin Ladeveze via Digitalmars-d-learn
wrote:
> On Friday, 19 June 2015 at 13:38:45 UTC, Steven Schveighoffer
> wrote:
> >
> > Does this work for you, or is there a further expectation?
> >
> > auto asTuple() { return Tuple!(int, "a", ...)(a, b,
> > stringValue);}
> >
> > -Steve
>
> In fact, I was trying to use traits to create the tuple
> automatically and being able to add or remove methods to the
> struct without breaking the asTuple method.
> I used allMembers for the name of the methods, but I didn't found
> anything for their return types or their values.
>
> Thank you.
http://dlang.org/phobos/std_traits.html#ReturnType
http://dlang.org/phobos/std_traits.html#ParameterTypeTuple
Re: Return types of the methods of a struct
On Friday, 19 June 2015 at 13:38:45 UTC, Steven Schveighoffer
wrote:
Does this work for you, or is there a further expectation?
auto asTuple() { return Tuple!(int, "a", ...)(a, b,
stringValue);}
-Steve
In fact, I was trying to use traits to create the tuple
automatically and being able to add or remove methods to the
struct without breaking the asTuple method.
I used allMembers for the name of the methods, but I didn't found
anything for their return types or their values.
Thank you.
Re: Return types of the methods of a struct
On Friday, 19 June 2015 at 13:40:01 UTC, Baz wrote:
On Friday, 19 June 2015 at 13:27:15 UTC, Quentin Ladeveze wrote:
On Friday, 19 June 2015 at 13:26:03 UTC, Steven Schveighoffer
wrote:
[...]
Thank you :)
Here is th corrected version :
Hi,
I have a struct with some methods int it, let's say
```
struct Example{
int a(){
return someValue;
}
float b(){
return someOtherValue;
}
string stringValue(){
return c;
}
}
Is there any way to have a asTuple method in this struct that
would returns something like :
Tuple!(int, "a", float, "b", string, "c")
and that will contain the values of the methods of the struct ?
Thanks.
in the declaration set the return type to 'auto'.
Use 'tuple' instead of 'Tuple'.
Ah, damn, haven't see Steven Schveighoffer answer while i was
writing. cross post. same thing.
Re: Return types of the methods of a struct
On 6/19/15 9:27 AM, Quentin Ladeveze wrote:
On Friday, 19 June 2015 at 13:26:03 UTC, Steven Schveighoffer wrote:
On 6/19/15 9:13 AM, Quentin Ladeveze wrote:
On Friday, 19 June 2015 at 13:12:08 UTC, Quentin Ladeveze wrote:
Hi,
I have a struct with some methods int it, let's say
```
struct Example{
int intValue(){
Hum. How can I delete a post ?
You can't. The forum is backed by a newsgroup, just post the full
corrected version :)
-Steve
Thank you :)
Here is th corrected version :
Hi,
I have a struct with some methods int it, let's say
```
struct Example{
int a(){
return someValue;
}
float b(){
return someOtherValue;
}
string stringValue(){
return c;
}
}
Is there any way to have a asTuple method in this struct that would
returns something like :
Tuple!(int, "a", float, "b", string, "c")
and that will contain the values of the methods of the struct ?
Does this work for you, or is there a further expectation?
auto asTuple() { return Tuple!(int, "a", ...)(a, b, stringValue);}
-Steve
Re: Return types of the methods of a struct
On Friday, 19 June 2015 at 13:27:15 UTC, Quentin Ladeveze wrote:
On Friday, 19 June 2015 at 13:26:03 UTC, Steven Schveighoffer
wrote:
On 6/19/15 9:13 AM, Quentin Ladeveze wrote:
[...]
You can't. The forum is backed by a newsgroup, just post the
full corrected version :)
-Steve
Thank you :)
Here is th corrected version :
Hi,
I have a struct with some methods int it, let's say
```
struct Example{
int a(){
return someValue;
}
float b(){
return someOtherValue;
}
string stringValue(){
return c;
}
}
Is there any way to have a asTuple method in this struct that
would returns something like :
Tuple!(int, "a", float, "b", string, "c")
and that will contain the values of the methods of the struct ?
Thanks.
in the declaration set the return type to 'auto'.
Use 'tuple' instead of 'Tuple'.
Re: Return types of the methods of a struct
On Friday, 19 June 2015 at 13:26:03 UTC, Steven Schveighoffer
wrote:
On 6/19/15 9:13 AM, Quentin Ladeveze wrote:
On Friday, 19 June 2015 at 13:12:08 UTC, Quentin Ladeveze
wrote:
Hi,
I have a struct with some methods int it, let's say
```
struct Example{
int intValue(){
Hum. How can I delete a post ?
You can't. The forum is backed by a newsgroup, just post the
full corrected version :)
-Steve
Thank you :)
Here is th corrected version :
Hi,
I have a struct with some methods int it, let's say
```
struct Example{
int a(){
return someValue;
}
float b(){
return someOtherValue;
}
string stringValue(){
return c;
}
}
Is there any way to have a asTuple method in this struct that
would returns something like :
Tuple!(int, "a", float, "b", string, "c")
and that will contain the values of the methods of the struct ?
Thanks.
Re: Return types of the methods of a struct
On 6/19/15 9:13 AM, Quentin Ladeveze wrote:
On Friday, 19 June 2015 at 13:12:08 UTC, Quentin Ladeveze wrote:
Hi,
I have a struct with some methods int it, let's say
```
struct Example{
int intValue(){
Hum. How can I delete a post ?
You can't. The forum is backed by a newsgroup, just post the full
corrected version :)
-Steve
Return types of the methods of a struct
Hi,
I have a struct with some methods int it, let's say
```
struct Example{
int intValue(){
Re: Return types of the methods of a struct
On Friday, 19 June 2015 at 13:12:08 UTC, Quentin Ladeveze wrote:
Hi,
I have a struct with some methods int it, let's say
```
struct Example{
int intValue(){
Hum. How can I delete a post ?
Re: best way to interface D code to Excel
On Thursday, 18 June 2015 at 11:36:50 UTC, Arjan wrote: See the 'COM in plain C' articles by Jeff Glatt which demonstrate how to do it using C. This might give you the information needed to do it using D. http://www.codeproject.com/Articles/Jeff-Glatt#articles. It's a little misleading though. It starts with complaining that existing examples hide details and then uses all sorts of macros which have the same issue. HRESULT PASCAL DllGetClassObject Hehe, this one doesn't use pascal convention of course :)
