Add unit scaling for display.

Author: thejpster

examples/format_test.rs

@@ -3,13 +3,15 @@ use measurements::Temperature;
 use measurements::Length;
 use measurements::Pressure;
 use measurements::Volume;
+use measurements::Weight;
 fn main() {
-	let t = Temperature::from_celsius(123.456);
-	let d = Length::from_meters(123.456);
-	let p = Pressure::from_millibars(123.456);
-	let v = Volume::from_litres(123.456);
-	println!("Temp of {0:.5} outside", t);
-	println!("Distance of {0:.5}", d);
-	println!("Pressure of {0:.5}", p);
-	println!("Volume of {0:.5}", v);
+	for power in -9..9 {
+		let val: f64 = 123.456 * (10.0f64.powf(power as f64));
+		println!("10^{}...", power);
+		println!("Temp of {0:.3} outside", Temperature::from_kelvin(val));
+		println!("Distance of {0:.3}", Length::from_meters(val));
+		println!("Pressure of {0:.3}", Pressure::from_millibars(val));
+		println!("Volume of {0:.3}", Volume::from_litres(val));
+		println!("Weight of {0:.3}", Weight::from_kilograms(val));
+	}
 }

src/length.rs

@@ -155,6 +155,25 @@ impl Measurement for Length {
     fn get_base_units_name(&self) -> &'static str {
         "m"
     }
+
+    fn get_appropriate_units(&self) -> (&'static str, f64) {
+        if self.meters >= 1_000_000_000.0 {
+            ("million km", self.meters / 1000_000_000.0)
+        } else if self.meters >= 1_000.0 {
+            ("km", self.meters / 1000.0)
+        } else if self.meters < 0.000_000_1 {
+            ("nm", self.meters * 1_000_000_000.0)
+        } else if self.meters < 0.000_1 {
+            ("\u{00B5}m", self.meters * 1_000_000.0)
+        } else if self.meters < 0.1 {
+            ("mm", self.meters * 1000.0)
+        } else if self.meters < 1.0 {
+            ("cm", self.meters * 100.0)
+        } else {
+            ("m", self.meters)
+        }
+    }
+
 }
 
 implement_measurement! { Length }

src/measurement.rs

@@ -35,11 +35,8 @@
 /// fn main() { }
 /// ```
 pub trait Measurement {
-    fn get_appropriate_units_name(&self) -> &'static str {
-        self.get_base_units_name()
-    }
-    fn get_appropriate_units(&self) -> f64 {
-        self.get_base_units()
+    fn get_appropriate_units(&self) -> (&'static str, f64) {
+        (self.get_base_units_name(), self.get_base_units())
     }
     fn get_base_units_name(&self) -> &'static str;
     fn get_base_units(&self) -> f64;
@@ -56,8 +53,9 @@ macro_rules! implement_display {
             fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
                 let p = f.precision().unwrap_or(1);
                 let w = f.width().unwrap_or(0);
+                let (unit, value) = self.get_appropriate_units();
                 write!(f, "{value:width$.prec$}\u{00A0}{unit}",
-                    prec=p, width=w, value=self.get_appropriate_units(), unit=self.get_appropriate_units_name())
+                    prec=p, width=w, value=value, unit=unit)
             }
         }
     )*)

src/pressure.rs

@@ -87,6 +87,14 @@ impl Measurement for Pressure {
     fn get_base_units_name(&self) -> &'static str {
         "mbar"
     }
+
+    fn get_appropriate_units(&self) -> (&'static str, f64) {
+        if self.millibars >= 1_000.0 {
+            ("bar", self.millibars / 1000.0)
+        } else {
+            ("mbar", self.millibars)
+        }
+    }
 }
 
 implement_measurement! { Pressure }

src/volume.rs

@@ -210,6 +210,18 @@ impl Measurement for Volume {
         "l"
     }
 
+    fn get_appropriate_units(&self) -> (&'static str, f64) {
+        if self.litres >= 1_000.0 {
+            ("m\u{00B3}", self.litres / 1000.0)
+        } else if self.litres < 0.000_1 {
+            ("\u{00B5}l", self.litres * 1_000_000.0)
+        } else if self.litres < 1.0 {
+            ("ml", self.litres * 1000.0)
+        } else {
+            ("l", self.litres)
+        }
+    }
+
 }
 
 implement_measurement! { Volume }

src/weight.rs

@@ -156,6 +156,20 @@ impl Measurement for Weight {
         "kg"
     }
 
+    fn get_appropriate_units(&self) -> (&'static str, f64) {
+        if self.kilograms >= 1_000.0 {
+            ("tonnes", self.kilograms / 1000.0)
+        } else if self.kilograms < 0.000_000_1 {
+            ("\u{00B5}g", self.kilograms * 1_000_000_000.0)
+        } else if self.kilograms < 0.000_1 {
+            ("mg", self.kilograms * 1_000_000.0)
+        } else if self.kilograms < 1.0 {
+            ("g", self.kilograms * 1000.0)
+        } else {
+            ("kg", self.kilograms)
+        }
+    }
+
 }
 
 implement_measurement! { Weight }