ANTLR Golang visitor got SIGSEGV about tsdb-ql HOT 3 CLOSED

After overriding the Visit method in AstBuilder I no longer have the nil error

func (b *AstBuilder) Visit(tree antlr.ParseTree) interface{} {
	return nil
}

so I guess BasewhileVisitor does not have Visit method? but why no compile error?

May need to list all the methods of a struct http://stackoverflow.com/questions/21397653/how-to-dump-methods-of-structs-in-golang

from tsdb-ql.

And using BasewhileVisitor also works, I think the problem is from embedding by pointer http://www.hydrogen18.com/blog/golang-embedding.html

Yes, it is https://groups.google.com/forum/#!topic/golang-nuts/ctRUq62cgME

One thing to keep in mind when you embed a pointer is that, well,
you're embedding a pointer. If you get a new(CardboardBox), then
RectPrism fields are not allocated yet - the pointer to the RectPrism
fields is zeroed.

And I don't think it's the case for visitor?

As to why one should use a pointer, one example is when one wants to
embed a struct containing unexported fields from another package.
Since the struct has unexported fields and is from a different
package, the -only- way to embed it is as a pointer. I proposed this
in another thread as a solution to provide a logger that closes its
output stream. Here's the reply:

from tsdb-ql.

So the problem is in the example, which use embedding by pointer

• it works for listener because base listener does not embed other things
• basevisitor embed BaseParseTreeVisitor, thus cause the nil problem when use it directly without explicit initialize the BaseTreeVisitor inside it

type PrinterwhileListener struct {
	*BasewhileListener
}
type BasewhileListener struct{}

type AstBuilder struct {
	*BasewhileVisitor
}

// tree.go
type BasewhileVisitor struct {
	*antlr.BaseParseTreeVisitor
}

// FIXME: this will cause SIGSEGV when using visit
func NewAstBuilder() *AstBuilder {
	return new(AstBuilder)
}

from tsdb-ql.