Less clever, lazy evaluation of parser method chain
This commit is contained in:
Timothy Warren
parent
a2ecaef5ee
commit
e4070abd40
102
src/lib.rs
102
src/lib.rs
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@ -79,38 +79,37 @@ impl JSON {
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}
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/// Parse a `JSONValue` from the current JSON string
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///
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/// This is probably an abuse of iterators...but it's still much better than the alternative
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/// of nested matches.
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///
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/// In order to determine the type of JSON value, each parse method is tried, until one
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/// matches, or a parse error happens.
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///
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/// * `Option`s implement IntoIterator, which returns an iterator of 0 or 1 items: the
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/// transferred (not borrowed) Some() value.
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/// * The `chain` method of iterators allows you to link iterators together,
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/// to act as one iterator
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/// * The first result from the iterator is the first parse method with a non-empty value,
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/// and should be the value wanted
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fn parse_value(&mut self) -> Result<JSONValue, ParseError> {
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self.skip_whitespace();
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let mut value = self
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.parse_string()?
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.into_iter()
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.chain(self.parse_number()?.into_iter())
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.chain(self.parse_object()?.into_iter())
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.chain(self.parse_array()?.into_iter())
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.chain(self.parse_keyword("true", JSONValue::True)?.into_iter())
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.chain(self.parse_keyword("false", JSONValue::False)?.into_iter())
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.chain(self.parse_keyword("null", JSONValue::Null)?.into_iter());
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match value.next() {
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Some(val) => Ok(val),
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None => Err(ParseError::UnexpectedEndOfInput(String::from(
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return if let Some(string) = self.parse_string()? {
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Ok(string)
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} else if let Some(number) = self.parse_number()? {
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Ok(number)
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} else if let Some(object) = self.parse_object()? {
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Ok(object)
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} else if let Some(array) = self.parse_array()? {
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Ok(array)
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} else if let Some(t) = self.parse_keyword("true", JSONValue::True)? {
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Ok(t)
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} else if let Some(f) = self.parse_keyword("false", JSONValue::False)? {
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Ok(f)
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} else if let Some(n) = self.parse_keyword("null", JSONValue::Null)? {
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Ok(n)
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} else {
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Err(ParseError::UnexpectedEndOfInput(String::from(
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"Doesn't seem to be valid JSON",
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))),
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}
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)))
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};
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// Eagerly evaluated simpler alternative to the original option iterator chain
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// let value = self.parse_string()?
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// .or(self.parse_number()?)
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// .or(self.parse_object()?)
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// .or(self.parse_array()?)
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// .or(self.parse_keyword("true", JSONValue::True)?)
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// .or(self.parse_keyword("false", JSONValue::False)?)
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// .or(self.parse_keyword("null", JSONValue::Null)?);
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}
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/// See if there's a `JSONValue::Object` next in the JSON
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@ -255,7 +254,7 @@ impl JSON {
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let start = self.i;
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// If it doesn't start with 0-9 or a minus sign, it's probably not a number
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if ! (self.chars[start].is_ascii_digit() || self.chars[start] == '-') {
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if !(self.chars[start].is_ascii_digit() || self.chars[start] == '-') {
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return Ok(None);
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}
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@ -297,11 +296,7 @@ impl JSON {
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// If there are numeric digits attempt to parse the digits as a number
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if n > start {
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let mut end = if n < self.chars.len() {
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n
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} else {
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max
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};
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let mut end = if n < self.chars.len() { n } else { max };
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// Hack to remove non-number characters
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if !self.chars[end].is_ascii_digit() {
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@ -313,8 +308,8 @@ impl JSON {
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match str.parse::<f64>() {
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Ok(number) => {
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self.increment(str.len());
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return Ok(Some(JSONValue::Number(number)))
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},
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return Ok(Some(JSONValue::Number(number)));
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}
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Err(e) => Err(ParseError::ExpectedDigit(format!("'{}', {:#?}", str, e))),
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}
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} else {
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@ -488,19 +483,37 @@ mod tests {
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// Number
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let res = JSON::parse("9.38083151965");
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assert_eq!(res, Ok(JSONValue::Number(9.38083151965)), "Failed to parse number");
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assert_eq!(
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res,
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Ok(JSONValue::Number(9.38083151965)),
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"Failed to parse number"
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);
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// String
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let res = JSON::parse(r#""/^$/""#);
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assert_eq!(res, Ok(JSONValue::String(String::from("/^$/"))), "Failed to parse string");
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assert_eq!(
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res,
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Ok(JSONValue::String(String::from("/^$/"))),
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"Failed to parse string"
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);
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// Number array
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let res = JSON::parse("[1, 2, 3]");
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assert_eq!(res, Ok(JSONValue::Array(vec![JSONValue::Number(1f64), JSONValue::Number(2f64), JSONValue::Number(3f64)])));
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assert_eq!(
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res,
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Ok(JSONValue::Array(vec![
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JSONValue::Number(1f64),
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JSONValue::Number(2f64),
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JSONValue::Number(3f64)
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]))
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);
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// Object array
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let result = JSON::parse("[{}]");
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assert_eq!(result, Ok(JSONValue::Array(vec![JSONValue::Object(HashMap::new())])));
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assert_eq!(
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result,
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Ok(JSONValue::Array(vec![JSONValue::Object(HashMap::new())]))
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);
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}
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#[test]
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@ -512,8 +525,10 @@ mod tests {
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#[test]
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fn can_parse_arbitrary_json() {
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let result = JSON::parse(r#"[{ "a": 9.38083151965, "b": 4e3 }]"#);
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assert!(result.is_ok(), format!("Failed on just number values: {:#?}", result));
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assert!(
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result.is_ok(),
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format!("Failed on just number values: {:#?}", result)
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);
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let result = JSON::parse(
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r#"[{
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@ -529,7 +544,8 @@ mod tests {
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}
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},
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"i": ["\"", "\\", "/", "\b", "\f", "\n", "\r", "\t", "\u0001", "\uface"]
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}]"#);
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}]"#,
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);
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assert!(result.is_ok(), format!("{:#?}", result));
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}
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}
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