Add possibility to add functions as messages to the logger

Author: smotastic

lib/src/printers/pretty_printer.dart

@@ -228,11 +228,12 @@ class PrettyPrinter extends LogPrinter {
   }
 
   String stringifyMessage(dynamic message) {
-    if (message is Map || message is Iterable) {
+    final finalMessage = message is Function ? message() : message;
+    if (finalMessage is Map || finalMessage is Iterable) {
       var encoder = JsonEncoder.withIndent('  ', toEncodableFallback);
-      return encoder.convert(message);
+      return encoder.convert(finalMessage);
     } else {
-      return message.toString();
+      return finalMessage.toString();
     }
   }
 

lib/src/printers/simple_printer.dart

@@ -48,11 +48,12 @@ class SimplePrinter extends LogPrinter {
   }
 
   String _stringifyMessage(dynamic message) {
-    if (message is Map || message is Iterable) {
+    final finalMessage = message is Function ? message() : message;
+    if (finalMessage is Map || finalMessage is Iterable) {
       var encoder = JsonEncoder.withIndent(null);
-      return encoder.convert(message);
+      return encoder.convert(finalMessage);
     } else {
-      return message.toString();
+      return finalMessage.toString();
     }
   }
 }

test/printers/simple_printer_test.dart

@@ -88,4 +88,19 @@ void main() {
       '[D]  [1,2,3,4]  ERROR: some error',
     );
   });
+
+  test('deal with Function type message', () {
+    var expectedMessage = 'heavily computed Message';
+    var withFunction = LogEvent(
+      Level.debug,
+      () => expectedMessage,
+      'some error',
+      StackTrace.current,
+    );
+
+    expect(
+      plainPrinter.log(withFunction)[0],
+      '[D]  $expectedMessage  ERROR: some error',
+    );
+  });
 }