Created
May 16, 2019 11:01
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use std::marker::PhantomData; | |
use std::convert::TryFrom; | |
use std::convert::TryInto; | |
#[derive(Debug)] | |
struct ConversionError; | |
struct ResultSet<T> { | |
column_names: Vec<String>, | |
rows: Vec<Vec<i32>>, | |
t: PhantomData<T>, | |
} | |
impl<T> ResultSet<T> { | |
fn pop<'rs>(&'rs mut self) -> Option<RowWithSchema<'rs>> { | |
let column_names = self.column_names.as_slice(); | |
self.rows.pop().map(|columns| RowWithSchema { | |
column_names, | |
columns, | |
}) | |
} | |
} | |
struct RowWithSchema<'rs> { | |
column_names: &'rs[String], | |
columns: Vec<i32>, | |
} | |
#[derive(Debug)] | |
struct Row(Vec<i32>); | |
impl<T> Iterator for ResultSet<T> where T: for<'rs> TryFrom<RowWithSchema<'rs>, Error = ConversionError> { | |
type Item = Result<T, ConversionError>; | |
fn next(&mut self) -> Option<Result<T, ConversionError>> { | |
self.pop().map(|r| r.try_into()) | |
} | |
} | |
impl<'rs> TryFrom<RowWithSchema<'rs>> for Row { | |
type Error = ConversionError; | |
fn try_from(r: RowWithSchema<'rs>) -> Result<Row, ConversionError> { | |
Ok(Row(r.columns)) | |
} | |
} | |
fn main() { | |
let rs: ResultSet<Row> = ResultSet { | |
column_names: vec!["foo".to_owned(), "bar".to_owned()], | |
rows: vec![ | |
vec![1, 2], | |
vec![3, 4], | |
], | |
t: PhantomData, | |
}; | |
for row in rs { | |
println!("{:?}", row); | |
} | |
} |
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