• Yuxuan Shui (4/4) Jun 15 2015 I have a template class which is derived from a base class. Is it
• Steven Schveighoffer (6/9) Jun 15 2015 No. You can't get compile-time information at runtime, unless you have
• Yuxuan Shui (14/25) Jun 15 2015 Well I don't have a serious use case of this. I just started
• Yuxuan Shui (3/18) Jun 15 2015 Maybe I can put a virtual function in the class that return the
• =?UTF-8?B?QWxpIMOHZWhyZWxp?= (3/5) Jun 15 2015 Yeah, that's how I would do it.
• Baz (14/15) Jun 15 2015 yes, you can compare instance of TypeInfo using is or '==' too,

"Yuxuan Shui" <yshuiv7 gmail.com> writes:

I have a template class which is derived from a base class. Is it 
possible to extract the template parameter from a reference to 
the base class?

Can is() operate on TypeInfo?

Steven Schveighoffer <schveiguy yahoo.com> writes:

On 6/15/15 2:10 PM, Yuxuan Shui wrote:
 I have a template class which is derived from a base class. Is it
 possible to extract the template parameter from a reference to the base
 class?

No. You can't get compile-time information at runtime, unless you have 
stored it somewhere that runtime can read.

But perhaps you can further describe your requirement, and a solution 
might be available.

-Steve

"Yuxuan Shui" <yshuiv7 gmail.com> writes:

On Monday, 15 June 2015 at 18:30:55 UTC, Steven Schveighoffer 
wrote:
 On 6/15/15 2:10 PM, Yuxuan Shui wrote:
 I have a template class which is derived from a base class. Is 
 it
 possible to extract the template parameter from a reference to 
 the base
 class?

 No. You can't get compile-time information at runtime, unless 
 you have stored it somewhere that runtime can read.

 But perhaps you can further describe your requirement, and a 
 solution might be available.

 -Steve

Well I don't have a serious use case of this. I just started 
using D couple of weeks ago, and is now experimenting with it by 
writing a toy compiler.

What I'm doing is I'm abusing the D type system to represent 
types in my toy language. I store type information into template 
parameters, and when I need to type check, I just use typeid and 
compare the result. Now I want to generate different code when I 
encounter different types, and for that I want to get the 
template parameters.

Of course if this is not possible I can always go back to 
implement my own type system properly. It's just a good thing to 
have.

"Yuxuan Shui" <yshuiv7 gmail.com> writes:

On Monday, 15 June 2015 at 22:56:57 UTC, Yuxuan Shui wrote:
 On Monday, 15 June 2015 at 18:30:55 UTC, Steven Schveighoffer 
 wrote:
 [...]

 Well I don't have a serious use case of this. I just started 
 using D couple of weeks ago, and is now experimenting with it 
 by writing a toy compiler.

 What I'm doing is I'm abusing the D type system to represent 
 types in my toy language. I store type information into 
 template parameters, and when I need to type check, I just use 
 typeid and compare the result. Now I want to generate different 
 code when I encounter different types, and for that I want to 
 get the template parameters.

 Of course if this is not possible I can always go back to 
 implement my own type system properly. It's just a good thing 
 to have.

Maybe I can put a virtual function in the class that return the 
template parameter?

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

On 06/15/2015 04:04 PM, Yuxuan Shui wrote:

 Maybe I can put a virtual function in the class that return the template
 parameter?

Yeah, that's how I would do it.

Ali

"Baz" <bb.temp gmx.com> writes:

On Monday, 15 June 2015 at 18:10:34 UTC, Yuxuan Shui wrote:
 Can is() operate on TypeInfo?

yes, you can compare instance of TypeInfo using is or '==' too, 
using typeid which
is returns at run-time the TypeInfo of the argument:

---
void main()
{
     assert(typeid(2) == typeid(1));
     assert(typeid(2) is typeid(1));
     Object a = new Object;
     Object b = new Object;
     assert(typeid(b) is typeid(a));
}
---