piotrwyrw / polymine Goto Github PK

Example:

func main() of number {
    // ..
}

i.e.

"func" identifier "(" { name ":" type ( "," ) } ")" "of" type decorated-block

Implement an internal mechanism for referencing node without risking a double-free case.

The issue arises, once a node pointer is not unique to the parent node, but is instead used across multiple nodes in the AST. During the deallocation process of the AST, the same node(s) will be deallocated multiple times, leading to a memory violation.

One potential fix to this issue might be the addition of a special reference node, which indicated to the astnode free-ing function, that the node is a reference to another node and shall not be freed.

Potential design challenges arise when accessing the values stored within the AST, since it's not obvious, and frankly quite random, when a node is a reference and when it is not. I consider a function ("unwrap" ?) that returns the raw node pointer and dereferences as necessary.

The alternative - copying the original AST for the semantic analysis stage, and freeing the structure on the original tree with no self-references - comes with a wide range of performance disadvantages which we are not willing to take.