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What does it mean for two objects to be equal?
According to the rules of the game, towers
can't be placed directly on the path.
0:00
We need a way to know if a map
location is on the path.
0:04
Let's add another method to the Path
class that will return true,
0:08
if the map location passed in,
is on the path.
0:12
So we'll say public bool IsOnPath and
0:15
it will take a MapLocation as a parameter.
0:19
And this method, will loop through all
of the locations in the path array.
0:26
So we'll say,
foreach(var pathLocation in _path,
0:31
And if the location passed in
equals one of the path locations,
0:40
We'll return true immediately.
0:48
Otherwise, if we get through all
of the locations on the path and
0:52
we get down here to the end of
the four H loop we'll return false.
0:56
Because we didn't find a matching
location in the path array.
1:01
To test this, let's create a map
location that is on the path.
1:05
For now,
we'll just do this in the Game.cs file.
1:09
So here we have our path.
1:13
Under here,
let's create a new MapLocation.
1:15
And we'll have it be right at
the beginning of the path, so
1:22
right here at 0, 2.
1:26
Just copy that down there.
1:31
Now we can say if(path.IsOnPath and
1:33
pass in that location we just created.
1:37
Then on the console will print,
1:46
location + " is on the path".
1:53
And just so we don't continue down into
our program we'll return right here.
2:00
Let's go ahead and compile and run this.
2:06
Hm.
2:18
We didn't see our message.
2:19
We should have seen this
message printed to the console.
2:21
And we shouldn't have seen any of this
stuff because we would have returned.
2:29
We must have a bug in the IsOnPath method.
2:33
Let's take a second look.
2:36
On the surface it looks correct,
doesn't it?
2:37
There's something very
subtle happening here.
2:41
This double equals sign checks to see if
two variables refer to the same object.
2:43
This is different than two locations
on the map being the same.
2:50
Let's go back to Game.cs to see
the MapLocation objects that should have
2:54
caused the IsOnPath method to return true.
2:58
Here's the MapLocation that's
in the path array, and
3:06
here's the MapLocation that
we're checking against.
3:09
They may look the same, but these
are actually two very different objects.
3:13
See, here we created a new MapLocation and
put it in this array, and
3:18
down here we created a completely
different MapLocation.
3:22
They just so happen to refer to
the same location on the map.
3:26
It's like they're identical twins.
3:30
They aren't the same person,
but they look identical.
3:32
The equality operator by default,
3:36
only checks to see if they
are the exact same object.
3:38
Or in the case of twins,
the exact same person.
3:42
On the computer, these two objects
sit in different locations in memory.
3:45
The equality operator actually just calls
the static, system.object.ReferenceEqual
3:50
method to determine if two variables
refer to the same location in memory.
3:55
In which case, they are the same object.
4:00
If two variables refer to
the same object in memory,
4:03
we can say that they
have reference equality.
4:06
That's all that double equals
equality operator checks for.
4:09
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