Re: macros (was: Seeking computer-programming job (Sunnyvale, CA))

From:

Lew <lew@lewscanon.com>

Newsgroups:

comp.lang.lisp,comp.lang.java.programmer

Date:

Fri, 15 May 2009 07:34:26 -0700 (PDT)

Message-ID:

<5fb30931-4310-4e77-a967-460539bf9248@n8g2000vbb.googlegroups.com>

Stefan Ram wrote:

  The same coded in Java without macros /is/ more verbose,
  but also more readable to someone who knows Java:

public static String getMultiValue( Object valueObject )
{ String result = null;
  if( valueObject == null )result = null;

  else if( valueObject instanceof StringValue )
  { StringValue stringValue =( StringValue )valueObject;
    result = getStringValue( stringValue ); }

  else if( valueObject instanceof SprayValue )
  { SprayValue setValue =( SprayValue )valueObject;
    result = getSetValue( setValue ); }

  return result; }

An experienced Java programmer will see this series of 'instanceof'
operators and look for a way to code the thing polymorphically.

interface Multi<T>
{
   public String getValue( T arg );
}
class StringVersion implements Multi<String>
{
   public String getValue( String arg )
   {
     return getStringValue( arg );
   }
}
class SprayVersion implements Multi<Spray>
{
   public String getValue( Spray arg )
   {
    return getSprayValue( arg );
   }
}

etc.

--
Lew