On Tue, 26 Mar 2019, at 12:37 PM, XiaoBing Jiang wrote:
> Hi, all:
>
> in src/cmd/compile/internal/syntax/nodes.go, why need the aNode() function in
> the interface?
>
> type Node interface {
> // Pos() returns the position associated with the node as follows:
> // 1) The position of a node representing a terminal syntax production
> // (Name, BasicLit, etc.) is the position of the respective production
> // in the source.
> // 2) The position of a node representing a non-terminal production
> // (IndexExpr, IfStmt, etc.) is the position of a token uniquely
> // associated with that production; usually the left-most one
> // ('[' for IndexExpr, 'if' for IfStmt, etc.)
> Pos() Pos
> aNode()
> }
>
> type node struct {
> // commented out for now since not yet used
> // doc *Comment // nil means no comment(s) attached
> pos Pos
> }
>
> func (n *node) Pos() Pos { return n.pos }
> func (*node) aNode() {}
>
It prevents implementations of the interface outside of that package. The code
can then assume it knows all the possible implementations of Node.
Ian
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