Add support for acres

src/conversions.rs

@@ -75,6 +75,11 @@ fn get_conversion(unit: NonMetric) -> Conversion {
 			from: inch_from * inch_from,
 			to: MetricQuantity { amount: 12.0 * inch_to * 12.0 * inch_to, unit: Metric::SquareMetre },
 		},
+		NonMetric::Acre => Conversion {
+			offset: 0.0,
+			from: inch_from * inch_from,
+			to: MetricQuantity { amount: 43_560.0 * 12.0 * inch_to * 12.0 * inch_to, unit: Metric::SquareMetre },
+		},
 	}
 }
 
@@ -128,6 +133,7 @@ mod test {
 		let tests = [
 			Test(NonMetric::SquareInch, 0.00064516),
 			Test(NonMetric::SquareFoot, 0.09290304),
+			Test(NonMetric::Acre, 4046.8564224),
 		];
 		run_tests(&tests, Metric::SquareMetre);
 	}

src/lib.rs

@@ -75,6 +75,7 @@ fn unit_to_name(unit: NonMetric) -> &'static str {
 		// Area
 		NonMetric::SquareInch => "square inches",
 		NonMetric::SquareFoot => "square feet",
+		NonMetric::Acre => "acres",
 	}
 }
 
@@ -110,5 +111,6 @@ mod test {
 		// Area
 		assert_eq!(run("1 in²"), Ok("6.452 cm²".to_string()));
 		assert_eq!(run("1 ft²"), Ok("929 cm²".to_string()));
+		assert_eq!(run("1 acre"), Ok("4 047 m²".to_string()));
 	}
 }

src/parse.rs

@@ -110,6 +110,10 @@ fn parse_unit(input: String) -> Result<NonMetric, ParseError> {
 		"feet²" => Ok(NonMetric::SquareFoot),
 		"ft²" => Ok(NonMetric::SquareFoot),
 
+		"acre" => Ok(NonMetric::Acre),
+		"acres" => Ok(NonMetric::Acre),
+		"ac" => Ok(NonMetric::Acre),
+
 		_ => Err(ParseError::UnknownUnit(input)),
 	}
 }
@@ -267,6 +271,10 @@ mod test {
 		assert_eq!(parse_unit("feet²".to_string()), Ok(NonMetric::SquareFoot));
 		assert_eq!(parse_unit("ft²".to_string()), Ok(NonMetric::SquareFoot));
 
+		assert_eq!(parse_unit("acre".to_string()), Ok(NonMetric::Acre));
+		assert_eq!(parse_unit("acres".to_string()), Ok(NonMetric::Acre));
+		assert_eq!(parse_unit("ac".to_string()), Ok(NonMetric::Acre));
+
 		// Unknown unit
 		assert_eq!(parse_unit("hutenosa".to_string()), Err(ParseError::UnknownUnit("hutenosa".to_string())));
 	}

src/units.rs

@@ -22,6 +22,7 @@ pub enum NonMetric {
 	// Area
 	SquareInch,
 	SquareFoot,
+	Acre,
 }
 
 #[derive(Clone, Copy, Debug, PartialEq)]