Constify number parsing as well #33
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Reviewer's GuideRefactor number parsing by introducing a const state transition table and helper methods to replace the previous manual match arms in the tokenizer. Class diagram for updated number parsing in TokenizerclassDiagram
class Tokenizer {
+const NUM_TRANSITIONS: [[Option<Num>; 256]; 8]
+const fn num_to_index(num: &Num) -> usize
+fn process_number_transition(&self, current_num: &Num, ch: u8) -> Option<Num>
+fn is_valid_number_terminal_state(&self, num_state: &Num) -> bool
}
class Num {
<<enum>>
Sign
LeadingZero
BeforeDecimalPoint
Decimal
AfterDecimalPoint
Exponent
ExponentSign
AfterExponent
}
Tokenizer --> Num : uses
Flow diagram for table-driven number parsing logicflowchart TD
A[Start Number Parsing] --> B{Current Num State}
B --> C[Lookup transition in NUM_TRANSITIONS]
C -->|Valid transition| D[Update Num State]
C -->|No transition| E{Is terminal state?}
E -->|Yes, valid terminator| F[Emit Number Token]
E -->|No, invalid| G[Error: Invalid Number]
F --> H[Continue Parsing]
D --> B
G --> H
File-Level Changes
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WalkthroughThe number parsing logic in the Tokenizer has been refactored from a large match statement to a table-driven state machine using a new transition table. Helper functions for state transitions and terminal state validation were added, and the Num enum was updated to support these changes. Changes
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Summary of Changes
Hello @kaidokert, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!
This pull request optimizes the JSON number parsing mechanism by moving its state transition logic into a compile-time constant table. This change aims to improve parsing performance by pre-computing transitions and simplifies the runtime code by replacing a verbose state machine with a more efficient table-driven lookup.
Highlights
- Enum Trait Derivations: The
Numenum now derivesCopyandPartialEqtraits, which are necessary to enable its use withinconstcontexts for compile-time evaluation. - Compile-Time Number Parsing Logic: A new
const NUM_TRANSITIONStable has been introduced. This table pre-calculates all possible state transitions for number parsing at compile time, effectively creating a finite state machine that can be queried efficiently. - Refactored Number Parsing State Machine: The runtime number parsing logic within the
process_token_charmethod has been significantly refactored. The largematchstatement that previously handled all number state transitions has been replaced with calls to new helper functions (process_number_transitionandis_valid_number_terminal_state) that leverage theconst NUM_TRANSITIONStable, resulting in more concise and potentially faster code.
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Hey @kaidokert - I've reviewed your changes and they look great!
Prompt for AI Agents
Please address the comments from this code review:
## Individual Comments
### Comment 1
<location> `picojson/src/ujson/tokenizer/mod.rs:355` </location>
<code_context>
+ };
+
+ // Convert Num enum to table index for NUM_TRANSITIONS
+ const fn num_to_index(num: &Num) -> usize {
+ match num {
+ Num::Sign => 0,
+ Num::LeadingZero => 1,
+ Num::BeforeDecimalPoint => 2,
+ Num::Decimal => 3,
+ Num::AfterDecimalPoint => 4,
+ Num::Exponent => 5,
+ Num::ExponentSign => 6,
+ Num::AfterExponent => 7,
+ }
+ }
+
</code_context>
<issue_to_address>
Passing Num by value instead of reference may be more idiomatic.
Since Num implements Copy, you can take num: Num instead of &Num in num_to_index and related functions to avoid unnecessary references and dereferencing.
Suggested implementation:
```rust
+ // Convert Num enum to table index for NUM_TRANSITIONS
+ const fn num_to_index(num: Num) -> usize {
+ match num {
+ Num::Sign => 0,
+ Num::LeadingZero => 1,
+ Num::BeforeDecimalPoint => 2,
+ Num::Decimal => 3,
+ Num::AfterDecimalPoint => 4,
+ Num::Exponent => 5,
+ Num::ExponentSign => 6,
+ Num::AfterExponent => 7,
+ }
+ }
```
If there are any other functions in this file (or related files) that take `&Num` as a parameter and do not require a reference, you should update their signatures and call sites to take `Num` by value instead, for consistency and idiomatic Rust style.
</issue_to_address>
### Comment 2
<location> `picojson/src/ujson/tokenizer/mod.rs:375` </location>
<code_context>
+ }
+
+ // Check if current number state can be terminated (not in the middle of parsing)
+ fn is_valid_number_terminal_state(&self, num_state: &Num) -> bool {
+ match num_state {
+ // These states represent valid complete numbers
+ Num::LeadingZero
+ | Num::BeforeDecimalPoint
+ | Num::AfterDecimalPoint
+ | Num::AfterExponent => true,
+ // These states are incomplete and cannot be terminated
+ Num::Sign | Num::Decimal | Num::Exponent | Num::ExponentSign => false,
+ }
+ }
pub fn new() -> Self {
</code_context>
<issue_to_address>
The &self receiver is not needed for is_valid_number_terminal_state.
Since is_valid_number_terminal_state doesn't access instance fields, consider making it a static method or free function to better indicate its statelessness.
Suggested implementation:
```rust
// Check if current number state can be terminated (not in the middle of parsing)
fn is_valid_number_terminal_state(num_state: &Num) -> bool {
match num_state {
// These states represent valid complete numbers
Num::LeadingZero
| Num::BeforeDecimalPoint
| Num::AfterDecimalPoint
| Num::AfterExponent => true,
// These states are incomplete and cannot be terminated
Num::Sign | Num::Decimal | Num::Exponent | Num::ExponentSign => false,
}
}
```
If there are any calls to `self.is_valid_number_terminal_state(...)` elsewhere in this file or module, they should be updated to `Self::is_valid_number_terminal_state(...)` or `Tokenizer::is_valid_number_terminal_state(...)` to reflect the method's new static status.
</issue_to_address>Help me be more useful! Please click 👍 or 👎 on each comment and I'll use the feedback to improve your reviews.
Summary by Sourcery
Refactor the JSON number parser to use a compile-time state transition table for handling digit, decimal, and exponent states, replacing the previous manual match-based state machine.
Enhancements:
NUM_TRANSITIONSlookup table to drive number parsing state transitionsprocess_number_transitionandis_valid_number_terminal_statehelper methods for table-driven parsing and validationCopyandPartialEqon theNumenum for ergonomic state handlingTokenizer::new()with a concise branch that uses the transition table and helpersSummary by CodeRabbit