use post_* visitors for mutable visits #789
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My initial implementation of mutable visitors closely matched the existing immutable visitor implementations, and used pre_* visitors (a mutable expression was first passed the visitor, then its children were visited). After some initial usage, I realize this actually impractical, and can easily lead to infinite recursion when one isn't careful. For instance a mutable visitor would replace x by f(x), then would be called again on the nested x and result in f(f(x)), then again resulting in f(f(f(x))), and so on. So, this commit changes the behavior of the visit_*_mut functions to call the visitor on an expression only once all of its children have been visited. It also makes the documentation more explicit and adds an example.
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AugustoFKL
approved these changes
Jan 5, 2023
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I am sorry I am a bit behind on reviews / merging in sqlparser-rs. I hope to be able to catch up later this week |
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Thank you for the contribution |
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Thanks for merging, @alamb ! |
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Thank you for the contribution @lovasoa |
Ziinc
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to Logflare/sqlparser-rs
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Jan 20, 2023
My initial implementation of mutable visitors closely matched the existing immutable visitor implementations, and used pre_* visitors (a mutable expression was first passed the visitor, then its children were visited). After some initial usage, I realize this actually impractical, and can easily lead to infinite recursion when one isn't careful. For instance a mutable visitor would replace x by f(x), then would be called again on the nested x and result in f(f(x)), then again resulting in f(f(f(x))), and so on. So, this commit changes the behavior of the visit_*_mut functions to call the visitor on an expression only once all of its children have been visited. It also makes the documentation more explicit and adds an example.
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My initial implementation of mutable visitors closely matched the existing immutable visitor implementations,
and used pre_* visitors (a mutable expression was first passed to the visitor, then its children were visited).
After some initial usage, I realize this is actually impractical, and can easily lead to infinite recursion when one isn't careful.
For instance a mutable visitor would replace x by f(x), then would be called again on the nested x and result in f(f(x)), then again resulting in f(f(f(x))), and so on.
So, this commit changes the behavior of the visit_*_mut functions to call the visitor on an expression only once all of its children have been visited.
It also makes the documentation more explicit and adds an example.