问题
In Smalltalk, there are two terms often found within a method body: self
and yourself
.
What is the difference between them?
回答1:
The reserved word self
is a pseudo variable (you cannot assign to it) that refers to the current receiver of the method where it is used. On the other side yourself
is a message you can send to any object to get that very same object.
The implementation of yourself
is
yourself
^self
meaning that the message yourself
will behave as I just explained.
The reason why yourself
exists is to support message cascading, where you put it as the last message to make sure the resulting expression will answer with the receiver:
^receiver
msg1;
msg2;
yourself
If msg2
might answer with something different from the receiver
you can append the yourself
message to ignore that answer and return receiver
instead. Of course you could have achieved the same result by writing:
receiver
msg1;
msg2.
^receiver
Because of the simplicity of these two examples, it might be hard to understand what the advantage would be. However, consider that receiver
is not a variable but a complex expression, something like.
^(self msg: arg1 arg: arg2)
msg1;
msg2;
yourself.
Without using yourself
you would have to add a temporary to save the value of the receiver to achieve the same:
| answer |
answer := self msg: arg1 arg: arg2.
answer
msg1;
msg2.
^answer
which is a little bit more verbose.
To summarize, self
is a reserved word that refers to the current receiver and yourself
is just a regular method that is there just for convenience.
回答2:
self
is a synonym for an object: specifically the receiver of the message that invoked the method. It is used within the body of a method.
yourself
is a message that you can send to an object, that returns the receiver of the message.
anObject yourself
returns anObject
.
yourself
is often used at the end of a message cascade within a method body.
When you want the return value from the method to be the receiver, but the final message in the cascade returns something else, you could write either:
self aMessageReturningTheReceiver;
aMessageReturningTheArgument: anArgument .
^self
or
self aMessageReturningTheReceiver;
aMessageReturningTheArgument: anArgument;
yourself
来源:https://stackoverflow.com/questions/33850170/what-is-the-difference-between-self-and-yourself-in-smalltalk