String, GString type and equality

This might be very schoolboy blog for some of you - I still hope that it might be useful to avoid some bugs.

Some weeks back my pair and I were fixing a bug that finally boiled down to the fact that the contains() method on a List returned false if the list contained the GString counterpart of the same literal.

Having played a bit I learned a couple of things about GStrings. Please find some bullet points and the code snippet bellow.

Type:
1. def var1 = "this is a String instead of a GString even if it is surrounded by double quotes - can has no dollar sign"
2. def var2 = "this is a GString because it contains a dollar sign - $var1"
3. String var3 = "this is a string because it was defined as a String"
4. String var4 = "$var3 - this is still a string because it was defined as a String"

Equality
1. a String and a GString can be ==
2. a String and a GString are NEVER equals()
3. as a consequence a list containing a literal will not return true if the type (GString/String) does not match

class WhereIsYourDummyTests extends GroovyTestCase {
def e = "y"
def dummy = "dumm$e"

void assertTypeIsStringForAFixGString() {
   assert e instanceof java.lang.String
   assert dummy instanceof groovy.lang.GString
}

void testEqualsNotEquals() {
    assert "dummy" == dummy
    assert dummy == "dummy"

    // WATCH OUT HERE
    assertFalse("dummy".equals(dummy))
    assertFalse(dummy.equals("dummy"))
}

void testContainsDoesntContain() {
   assert ['dummy'].contains("dummy")
   assert ["dummy"].contains('dummy')
   assert [dummy].contains(dummy)

   // THIS IS TRICKY:
   assert ![dummy].contains("dummy")
   assert ![dummy].contains('dummy')
   assert !["dummy"].contains(dummy)
   assert !['dummy'].contains(dummy)

   assert [dummy.toString()].contains("dummy")
   assert [dummy.toString()].contains('dummy')
}

void testContainsIfVariablesAreStringInsteadOfDef() {
   String e = "y"                  // String instead of def
   String dummy = "dumm$e"         // String instead of def

   assert ['dummy'].contains("dummy")
   assert ["dummy"].contains('dummy')
   assert [dummy].contains(dummy)

   assert [dummy].contains("dummy")
   assert [dummy].contains('dummy')
   assert ["dummy"].contains(dummy)
   assert ['dummy'].contains(dummy)

   assert [dummy.toString()].contains("dummy")
   assert [dummy.toString()].contains('dummy')
}
}