Type name resolution

In Meso, there is no data type named int or double. Every data type's name is a full UTL, such as meso:int or java:double. The UTL can be resolved from a type identifier against namespace and import statements similar to that in Java. The scheme of the namespace is also used to resolve the identifier.

For example, in the following program:

namespace meso:foo;
import imop:example.com/abc.*;
import java:java.foo.*;

class Service {
   Bar b;             // what UTL is this type identifier "Bar"?
}

When resolving the type identifier Bar, the Meso compiler will try to locate these data types:

meso:Bar
meso:foo.Bar
imop:example.com/abc.Bar
java:java.foo.Bar

If more than one is found, an ambiguous error will be thrown. One may use an explicit import statement, which has precedence over wildcard imports, to solve the problem:

namespace meso:foo;
import imop:example.com/abc.Bar;    // explicit import
import java:java.foo.*;

class Service {
   Bar b;
}

If more multiple Bar types is needed in code, just put its full UTL in code directly:

namespace meso:foo;

class Service {
   imop:example.com/abc.Bar b1;
   java:java.foo.Bar        b2;
}

Full UTL can be used in replace of a simple type identifier everywhere. For example, the following two programs are equivalent:

namespace meso:foo;

class Service implements java:java.lang.Runnable {
   public void run() {
      java:java.lang.System.out.println( "Howdy!" );
   }
}

namespace meso:foo;
import java:java.lang.*;

class Service implements Runnable {
   public void run() {
      System.out.println( "Howdy!" );
   }
}

Notice that the scheme of the namespace also participates the type resolution process. For example, in the following program, int is resolved as meso:int:

namespace meso:foo;

class Service {
   int x;              // meso:int
}