[antlr-interest] Custom AST Types

[Robert Colquhoun]

Hi Everyone,

Is anyone else having problems in tree walkers using custom AST types in 
conjunction with protected rules?

I get ClassCastExceptions whenever the rule tries to match nothing ie ASTNULL

ie

options{
     ASTLabelType=MyAST;
}
....
protected elsest: (#(ELSE statementblock))?

The code generated has something like:

  protected final void elsest(antlr.collections.AST _t) throws 
antlr.RecognitionException {

      MyAST elsest_AST_in = (MyAST)_t;  //<---ClassCastException here!
      .....

What appears to happen is that the elsest() rule is called passing ASTNULL 
when there is no else clause as part of a if/then/else statement and it 
trys to cast ASTNULL to MyAST type which breaks things.

To fix
	- either somehow change ASTNULL to be of MyAST type.
	- as in other parts of generated code use something like:
		MyAST elsest_AST_in = (_t == ASTNULL) ? null : (MyAST)_t;

Both require changes to antlr to solve though, otherwise i can hack my 
grammar to work around this i think.....just want to know if it is 
affecting other people at all, and thus whether i should fix antlr?

  - Robert


 

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