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digitalmars.D.learn - Question on Octal

reply "Michael" <pongad gmail.com> writes:
Hi all,
   I have just read Walter's article about octals on Dr. Dobb's. 
As a newbie, I tried to create one myself.

template octal(int n) {
	int toOct(int x) {...}
	
	enum octal = toOct(n);
}

void main() {
	import std.stdio : writeln;
	writeln(octal!10);
}

I have two questions about this.
1) The specification is clear that the if the template has only 
one member and the member has the same name with the template's, 
the member is implicitly referred to in the instantiation. The 
template octal has two members, so the program should not really 
be compiling, and yet it does. Is this a compiler bug?
2) I chose the declare the inner "octal" as an enum following 
Walter's example. But why enum? What would be different if it 
were auto, immutable, or static?

Thanks guys!
Michael
Aug 15 2012
next sibling parent "Jonathan M Davis" <jmdavisProg gmx.com> writes:
On Wednesday, August 15, 2012 19:49:53 Michael wrote:
 Hi all,
 I have just read Walter's article about octals on Dr. Dobb's.
 As a newbie, I tried to create one myself.
 
 template octal(int n) {
 int toOct(int x) {...}
 
 enum octal = toOct(n);
 }
 
 void main() {
 import std.stdio : writeln;
 writeln(octal!10);
 }
 
 I have two questions about this.
 1) The specification is clear that the if the template has only
 one member and the member has the same name with the template's,
 the member is implicitly referred to in the instantiation. The
 template octal has two members, so the program should not really
 be compiling, and yet it does. Is this a compiler bug?

If the spec says that you can only have one member in an eponymous template, then it's wrong and needs to be updated. All of the symbols which don't match the template name are private and are used only as helpers. TDPL (The D Programming Language by Andrei Alexandrescu) gives the correct description.
 2) I chose the declare the inner "octal" as an enum following
 Walter's example. But why enum? What would be different if it
 were auto, immutable, or static?

Normally, enum is used for values and alias is used for types. You _can_ use other stuff like auto if the result is a value, but if it doesn't generate a compile-time constant (which pretty much only enum and immutable will do), then it won't work in any context where the result must be known at compile time. And if you use immutable rather than enum, then that forces the result to be immutable, which may or may not be desirable. I don't think that I've ever seen anyone use anything other than enum or alias for the symbol which is the result of an eponymous template. - Jonathan M Davis
Aug 15 2012
prev sibling next sibling parent "Simen Kjaeraas" <simen.kjaras gmail.com> writes:
On Wed, 15 Aug 2012 20:07:59 +0200, Jonathan M Davis <jmdavisProg gmx.com>  
wrote:

 1) The specification is clear that the if the template has only
 one member and the member has the same name with the template's,
 the member is implicitly referred to in the instantiation. The
 template octal has two members, so the program should not really
 be compiling, and yet it does. Is this a compiler bug?

If the spec says that you can only have one member in an eponymous template, then it's wrong and needs to be updated. All of the symbols which don't match the template name are private and are used only as helpers. TDPL (The D Programming Language by Andrei Alexandrescu) gives the correct description.

And those symbols are only private if there is a member that matches the template name. Otherwise you'd have to resort to ugkly hacks to keep more than one piece of information in a template. -- Simen
Aug 15 2012
prev sibling parent Jonathan M Davis <jmdavisProg gmx.com> writes:
On Thursday, August 16, 2012 06:14:23 Simen Kjaeraas wrote:
 On Wed, 15 Aug 2012 20:07:59 +0200, Jonathan M Davis <jmdavisProg gmx.com>
 
 wrote:
 1) The specification is clear that the if the template has only
 one member and the member has the same name with the template's,
 the member is implicitly referred to in the instantiation. The
 template octal has two members, so the program should not really
 be compiling, and yet it does. Is this a compiler bug?

If the spec says that you can only have one member in an eponymous template, then it's wrong and needs to be updated. All of the symbols which don't match the template name are private and are used only as helpers. TDPL (The D Programming Language by Andrei Alexandrescu) gives the correct description.

And those symbols are only private if there is a member that matches the template name. Otherwise you'd have to resort to ugkly hacks to keep more than one piece of information in a template.

Well, if no member matches the template name, then it's not an eponymous template, and different rules apply. - Jonathan M Davis
Aug 15 2012