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digitalmars.D - mixins: Shouldn't this work?

reply mike <vertex gmx.at> writes:
Hi!

I've got this idea:

' import std.stdio;
'
' debug
' {
'     void trace(char[] T)()
'     {
'         scope (failure) writefln("Trace: ", T);
'     }
' }
' else
' {
'     void trace(char[] T)()
'     {
'     }
' }
'
' float foo(float x, float y)
' {
'     mixin trace!("foo");
'     return x / y;
' }
'
' void bar()
' {
'     writefln("result: ", foo(0., 0.));
' }

As far as I understand it, the "scope (failure) ..." would be mixed into=
  =

foo's scope, so as soon as foo throws, the trace message should be  =

displayed.

' mixin trace!("msg");

is much nicer than

' debug scope (failure) writefln("msg");

Oh, and congrats on 1.0! :)
Hope D gets picked up by lots of people now!

-mike

-- =

Erstellt mit Operas revolution=E4rem E-Mail-Modul: http://www.opera.com/=
mail/
Jan 03 2007
parent reply Kirk McDonald <kirklin.mcdonald gmail.com> writes:
mike wrote:

 Hi!
 
 I've got this idea:
 
 ' import std.stdio;
 '
 ' debug
 ' {
 '     void trace(char[] T)()
 '     {
 '         scope (failure) writefln("Trace: ", T);
 '     }
 ' }
 ' else
 ' {
 '     void trace(char[] T)()
 '     {
 '     }
 ' }
 '
 ' float foo(float x, float y)
 ' {
 '     mixin trace!("foo");
 '     return x / y;
 ' }
 '
 ' void bar()
 ' {
 '     writefln("result: ", foo(0., 0.));
 ' }
 
 As far as I understand it, the "scope (failure) ..." would be mixed 
 into  foo's scope, so as soon as foo throws, the trace message should 
 be  displayed.
 
 ' mixin trace!("msg");
 
 is much nicer than
 
 ' debug scope (failure) writefln("msg");
 
 Oh, and congrats on 1.0! :)
 Hope D gets picked up by lots of people now!
 
 -mike
 


Mixins are for mixing-in declarations, not statements. What you're doing 
is this:

float foo(float x, float y) {
     mixin trace!("foo");
     return x / y;
}

Becomes:

float foo(float x, float y) {
     void trace() {
         scope (failure) writefln("Trace: ", "foo");
     }
     return x / y;
}

See? The "scope (failure)" is inside a nested function. It applies to 
the scope of that function, and doesn't help one iota. :-)

-- 
Kirk McDonald
Pyd: Wrapping Python with D
http://pyd.dsource.org
Jan 03 2007
parent reply mike <vertex gmx.at> writes:
Am 04.01.2007, 00:27 Uhr, schrieb Kirk McDonald  =

<kirklin.mcdonald gmail.com>:


 Mixins are for mixing-in declarations, not statements. What you're doi=


ng  =


 is this:

 float foo(float x, float y) {
      mixin trace!("foo");
      return x / y;
 }

 Becomes:

 float foo(float x, float y) {
      void trace() {
          scope (failure) writefln("Trace: ", "foo");
      }
      return x / y;
 }

 See? The "scope (failure)" is inside a nested function. It applies to =


 =


 the scope of that function, and doesn't help one iota. :-)


Ow! I see. So no way to do that?

-mike

-- =

Erstellt mit Operas revolution=E4rem E-Mail-Modul: http://www.opera.com/=
mail/
Jan 03 2007
parent Daniel Keep <daniel.keep+lists gmail.com> writes:
mike wrote:

 Am 04.01.2007, 00:27 Uhr, schrieb Kirk McDonald  
 <kirklin.mcdonald gmail.com>:
 

 Mixins are for mixing-in declarations, not statements. What you're 
 doing  is this:

 float foo(float x, float y) {
      mixin trace!("foo");
      return x / y;
 }

 Becomes:

 float foo(float x, float y) {
      void trace() {
          scope (failure) writefln("Trace: ", "foo");
      }
      return x / y;
 }

 See? The "scope (failure)" is inside a nested function. It applies to  
 the scope of that function, and doesn't help one iota. :-)


 
 
 Ow! I see. So no way to do that?
 
 -mike
 


Since you can't mixin statements, not directly.  Any way you do it, you 
would end up using a function at some point, so you may as well just do 
that, and rely on the compiler to inline the function for you.

*Actually reads code*

Ooooh, I see what you're up to.  Hmm... that is a tricky one.  You could 
try using a templated function with a delegate parameter... I have no 
idea if this actually works; perhaps a template guru could help you with 
the details :P


 auto trace(T_Return)(char[] name, T_Return delegate() dg)
 {
     debug scope(failure) writefln("Trace: %s", name);
     return dg();
 }

 float foo(float x, float y)
 {
     return trace!(float)("foo",
     {
         return x / y;
     });
 }


NB: You might be able to remove the "!(float)" bit, I'm not sure.  I 
haven't really delved into the newer template stuff...

	-- Daniel
Jan 05 2007