• Jack Applegame (48/48) Mar 13 2017 I'm pretty sure that this code should compile
• Jack Applegame (1/1) Mar 13 2017 Is this a bug?
• Stefan Koch (15/16) Mar 13 2017 No it's not
• ag0aep6g (22/38) Mar 13 2017 I don't think that's it.
• ag0aep6g (11/31) Mar 13 2017 It compiles when it's a normal method instead of a destructor:
• Stefan Koch (2/40) Mar 13 2017 Try to use m.
• ag0aep6g (23/35) Mar 13 2017 Works no problem?

Jack Applegame <japplegame gmail.com> writes:

I'm pretty sure that this code should compile 
(https://dpaste.dzfl.pl/cf1e1ee6ef4b):

struct A(T) {
     ~this() {
         char[T.sizeof] data;
     }
}

struct B(T) {
     A!T foo;
}

struct C {
     B!C bar;
}

void main() {
     C c;
}

But it doesn't:
/d300/f416.d(3): Error: struct f416.C no size because of forward 
reference /d300/f416.d(12): Error: template instance f416.B!(C) 
error instantiating

Notice that the same C++ code compiles without problems:

template<typename T> struct A {
     ~A() {
         char data[sizeof(T)];
     }
};

template<typename T> struct B {
     A<T> foo;
};

struct C {
     B<C> bar;
};

int main() {
     C c;
}

A simple recursion is compiled successfully 
(https://dpaste.dzfl.pl/5a8ff73bfa88):

struct A(T) {
     ~this() {
         char[T.sizeof] data;
     }
}

struct C {
     A!C bar;
}

void main() {
     C c;
}

Jack Applegame <japplegame gmail.com> writes:

Is this a bug?

Stefan Koch <uplink.coder googlemail.com> writes:

On Monday, 13 March 2017 at 22:05:24 UTC, Jack Applegame wrote:
 Is this a bug?

No it's not

struct C
{
   B!C;
}
is an error.

Howto compute C ?       <------\
let's check the members;       |
The member needs a template.   |
Howto compute the template ?   |
let's compute the parameters.  |
What is the first Parameter ?  |
Its C.                         |
Howoto compute C        -------/

ag0aep6g <anonymous example.com> writes:

On 03/13/2017 11:58 PM, Stefan Koch wrote:
 On Monday, 13 March 2017 at 22:05:24 UTC, Jack Applegame wrote:
 Is this a bug?

 No it's not

 struct C
 {
   B!C;
 }
 is an error.

 Howto compute C ?       <------\
 let's check the members;       |
 The member needs a template.   |
 Howto compute the template ?   |
 let's compute the parameters.  |
 What is the first Parameter ?  |
 Its C.                         |
 Howoto compute C        -------/

I don't think that's it.

Here's a variant where B is not instantiated with C:

----
struct A()
{
     ~this() { enum s = C.sizeof; }
}

struct B() { A!() foo; }
struct C { B!() bar; }
----

How to compute C?
Check members.
For member `B!() bar;`, resolve `B!()`.
Check members of `B!()`.
For member `A!() foo;` resolve `A!()`.
Check members of `A!()`.
No members => size = 0 (or rather 1, I guess).
Bubble up.

But the compiler seems to get confused by the destructor. I guess it 
incorrectly(?) sees a need to analyze C again before it can finish up 
`A!()`?

ag0aep6g <anonymous example.com> writes:

On 03/13/2017 03:26 PM, Jack Applegame wrote:
 I'm pretty sure that this code should compile
 (https://dpaste.dzfl.pl/cf1e1ee6ef4b):

 struct A(T) {
     ~this() {
         char[T.sizeof] data;
     }
 }

 struct B(T) {
     A!T foo;
 }

 struct C {
     B!C bar;
 }

 void main() {
     C c;
 }

 But it doesn't:
 /d300/f416.d(3): Error: struct f416.C no size because of forward
 reference /d300/f416.d(12): Error: template instance f416.B!(C) error
 instantiating

It compiles when it's a normal method instead of a destructor:

----
struct A(T) {
     void m() {
         char[T.sizeof] data;
     }
}
/* ... rest as above ... */
----

I don't see how the destructor makes a difference. Soo, bug?

Stefan Koch <uplink.coder googlemail.com> writes:

On Monday, 13 March 2017 at 22:59:36 UTC, ag0aep6g wrote:
 On 03/13/2017 03:26 PM, Jack Applegame wrote:
 I'm pretty sure that this code should compile
 (https://dpaste.dzfl.pl/cf1e1ee6ef4b):

 struct A(T) {
     ~this() {
         char[T.sizeof] data;
     }
 }

 struct B(T) {
     A!T foo;
 }

 struct C {
     B!C bar;
 }

 void main() {
     C c;
 }

 But it doesn't:
 /d300/f416.d(3): Error: struct f416.C no size because of 
 forward
 reference /d300/f416.d(12): Error: template instance 
 f416.B!(C) error
 instantiating

 It compiles when it's a normal method instead of a destructor:

 ----
 struct A(T) {
     void m() {
         char[T.sizeof] data;
     }
 }
 /* ... rest as above ... */
 ----

 I don't see how the destructor makes a difference. Soo, bug?

Try to use m.

ag0aep6g <anonymous example.com> writes:

On 03/14/2017 12:02 AM, Stefan Koch wrote:
 On Monday, 13 March 2017 at 22:59:36 UTC, ag0aep6g wrote:

[...]
 ----
 struct A(T) {
     void m() {
         char[T.sizeof] data;
     }
 }
 /* ... rest as above ... */
 ----

 I don't see how the destructor makes a difference. Soo, bug?

 Try to use m.

Works no problem?

----
struct A(T) {
     void m() {
         char[T.sizeof] data;
         import std.stdio;
         writeln(T.sizeof);
     }
}

struct B(T) {
     A!T foo;
}

struct C {
     B!C bar;
}

void main() {
     C c;
     c.bar.foo.m();
}
----

Prints "1".