I've looked online for a meaning of the @ operator in Pharo, but couldn't find anything.
What's the meaning of the Pharo @ operator? For instance, why does 25@50 get evaluated as: "(25@50)"?
In Smalltalk, the @ symbol is used to create instances of the class Point. An instance of such a class has two ivars x and y. You can create a Point using the x:y: message, like this
Point x: 3 y: 4.
However, it is less verbose to use the message @ like this
3 @ 4
to create the same thing.
Note that while x:y: is a message you send to the class Point, the message @ 4 is sent to the integer 3. In other words, the former is a class message, the latter an instance message.
Note that, since many people write 3@4 instead of 3 @ 4, this has the risk of creating a surprising side effect. In fact
3@-4
should be (in principle) the Point with coordinates 3 and -4. However, the Smalltalk syntax is different and will parse it as the message with selector @- and argument 4 sent to the receiver 3. This is why some dialects make an exception so that the message is interpreted as 3 @ -4, which can be achieved by implementing the method @- in Number or by tweaking the parser.