• Henning Pohl (20/20) Mar 26 2013 struct S {
• =?UTF-8?B?QWxpIMOHZWhyZWxp?= (8/28) Mar 26 2013 Since alias this is for implicit conversions, it should be effective
• Jonathan M Davis (11/43) Mar 26 2013 We should be extremely careful with implicit conversions. They can be us...
• bearophile (4/8) Mar 26 2013 "alias this" is meant to be used in structs.
• bearophile (4/5) Mar 26 2013 On the other hand, unless the compiler refuses to compile a class

"Henning Pohl" <henning still-hidden.de> writes:

struct S {
     int value() {
     	return 1;
     }
}

class Base {
     S s;
     alias s this;
}

class Derived : Base {
     void func() {
         int i = value();
     }
}

Fails with "main.d(14): Error: undefined identifier value".
Explicitly casting this to Base works:

     void func() {
         int i = (cast(Base)this).value();
     }

Is this intended or a bug?

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 03/26/2013 04:58 PM, Henning Pohl wrote:
 struct S {
 int value() {
 return 1;
 }
 }

 class Base {
 S s;
 alias s this;
 }

 class Derived : Base {
 void func() {
 int i = value();
 }
 }

 Fails with "main.d(14): Error: undefined identifier value".
 Explicitly casting this to Base works:

 void func() {
 int i = (cast(Base)this).value();
 }

 Is this intended or a bug?

Since alias this is for implicit conversions, it should be effective 
only when Base is used as an S. It is not obvious in the previous code 
that the programmer really wanted that.

I like the current behavior. I wonder what others think.

Also, this works as well:

         int i = super.value();

Ali

"Jonathan M Davis" <jmdavisProg gmx.com> writes:

On Tuesday, March 26, 2013 17:24:20 Ali Çehreli wrote:
 On 03/26/2013 04:58 PM, Henning Pohl wrote:
 struct S {
 int value() {
 return 1;
 }
 }
 
 class Base {
 S s;
 alias s this;
 }
 
 class Derived : Base {
 void func() {
 int i = value();
 }
 }
 
 Fails with "main.d(14): Error: undefined identifier value".
 Explicitly casting this to Base works:
 
 void func() {
 int i = (cast(Base)this).value();
 }
 
 Is this intended or a bug?

 
 Since alias this is for implicit conversions, it should be effective
 only when Base is used as an S. It is not obvious in the previous code
 that the programmer really wanted that.
 
 I like the current behavior. I wonder what others think.

We should be extremely careful with implicit conversions. They can be useful, 
but it makes it _very_ easy to cause bugs (particularly with regards to 
templates where it can easily become the case that something passes a template 
constraint due to an implicit conversion but fails to actually work with the 
function).

I don't know what the intended behavior here is, but since we already have 
cases like having to alias base class functions in derived classes when they 
were overloaded or not be able to call the base class overload, it doesn't 
surprise me at all that it would work this way.

- Jonathan M Davis

"bearophile" <bearophileHUGS lycos.com> writes:

Henning Pohl:

 class Base {
     S s;
     alias s this;
 }

"alias this" is meant to be used in structs.

Bye,
bearophile

"bearophile" <bearophileHUGS lycos.com> writes:

 "alias this" is meant to be used in structs.

On the other hand, unless the compiler refuses to compile a class 
with an alias this, it should behave meaningfully.

Bye,
bearophile