sumtype: rename 'degrees' to 'value' in example

Strictly speaking, the Kelvin scale is not measured in degrees, so the
previous name was incorrect. Changing it in all cases preserves
consistency.

Fixes dlang#10540

Author: pbackus

std/sumtype.d

@@ -32,9 +32,9 @@ version (D_BetterC) {} else
 {
     import std.math.operations : isClose;
 
-    struct Fahrenheit { double degrees; }
-    struct Celsius { double degrees; }
-    struct Kelvin { double degrees; }
+    struct Fahrenheit { double value; }
+    struct Celsius { double value; }
+    struct Kelvin { double value; }
 
     alias Temperature = SumType!(Fahrenheit, Celsius, Kelvin);
 
@@ -48,29 +48,29 @@ version (D_BetterC) {} else
     {
         return Fahrenheit(
             t.match!(
-                (Fahrenheit f) => f.degrees,
-                (Celsius c) => c.degrees * 9.0/5 + 32,
-                (Kelvin k) => k.degrees * 9.0/5 - 459.4
+                (Fahrenheit f) => f.value,
+                (Celsius c) => c.value * 9.0/5 + 32,
+                (Kelvin k) => k.value * 9.0/5 - 459.4
             )
         );
     }
 
-    assert(toFahrenheit(t1).degrees.isClose(98.6));
-    assert(toFahrenheit(t2).degrees.isClose(212));
-    assert(toFahrenheit(t3).degrees.isClose(32));
+    assert(toFahrenheit(t1).value.isClose(98.6));
+    assert(toFahrenheit(t2).value.isClose(212));
+    assert(toFahrenheit(t3).value.isClose(32));
 
     // Use ref to modify the value in place.
     void freeze(ref Temperature t)
     {
         t.match!(
-            (ref Fahrenheit f) => f.degrees = 32,
-            (ref Celsius c) => c.degrees = 0,
-            (ref Kelvin k) => k.degrees = 273
+            (ref Fahrenheit f) => f.value = 32,
+            (ref Celsius c) => c.value = 0,
+            (ref Kelvin k) => k.value = 273
         );
     }
 
     freeze(t1);
-    assert(toFahrenheit(t1).degrees.isClose(32));
+    assert(toFahrenheit(t1).value.isClose(32));
 
     // Use a catch-all handler to give a default result.
     bool isFahrenheit(Temperature t)