为什么 ifTrue 和 ifFalse 不用 ; 分隔在小话中？
a > b
ifTrue:[ 'greater' ]
ifFalse:[ 'less or equal' ]
我的理解是布尔 a > b 收到消息 ifTrue:[ 'greater' ]，然后收到消息 ifFalse:[ 'less or equal' ] 符合泛化：
objectInstance selector; selector2
但是这里需要一个分号来表明selector2 的接收者不是(objectInstance 选择器)而是objectInstance。是不是和上面的条件执行一样？
a > b
ifTrue:[ 'greater' ]
ifFalse:[ 'less or equal' ]
My understanding is that Boolean a > b receives the message ifTrue:[ 'greater' ], and then ifFalse:[ 'less or equal' ] complying to the generalization:
objectInstance selector; selector2
But there a semicolon is needed to specify that the receiver of selector2 is not (objectInstance selector) but objectInstance. Is not the same with the above conditional execution?
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该方法的选择器是
Boolean>>ifTrue:ifFalse:，这意味着它是一个一个方法，带有两个参数，而不是两个带有一个参数的方法。因此，要调用该方法，您可以向其发送带有两个块参数的消息
ifTrue:ifFalse:。请注意，为了方便起见，还有方法
Boolean>>ifFalse:ifTrue:、Boolean>>ifTrue:和Boolean>>ifFalse:< /代码>。The selector of the method is
Boolean>>ifTrue:ifFalse:, which means it is one method with two parameters, not two methods with one parameter.Ergo, to invoke the method, you send it the message
ifTrue:ifFalse:with two block arguments.Note that for convenience reasons, there are also methods
Boolean>>ifFalse:ifTrue:,Boolean>>ifTrue:andBoolean>>ifFalse:.所有相关的内容都已经说过了，但仅供您娱乐：
如前所述，
只有一条消息 #'ifTrue:ifFalse:' 带有 2 个参数，发送到 rcvr 。该表达式的值是来自该消息发送的值。
相比之下：
是 2 个连续消息的级联（#'ifTrue:' 和 #'ifFalse:'），每条消息都有 1 个参数发送到rcvr。表达式的值是上次发送返回的值。
现在有趣的是，布尔值确实理解 ifTrue: / ifFalse: （每个都有 1 个参数），
因此您的代码适用于副作用（评估这些块），但不适用于其价值。
这意味着：
生成与： 相同的输出，
但是：
将在 msg 中生成与： 不同的值，具体
取决于 a 和 b 的值。尝试 (ab)=(1 2) 与 (ab)=(2 1)...
许多 Smalltalk 初学者的问题是他们将 ifXXX: 视为语法，实际上它是一个发送产生价值的消息。此外，semi 并不是像许多以前学过的语言那样的语句分隔符，而是一个排序消息发送结构。
对于初学者来说这是一个糟糕的陷阱，因为代码似乎适用于某些特定的值组合，而对于其他值组合却会产生有趣的结果。
希望您的单元测试能够涵盖这些；-)
编辑：要查看错误值的来源，请查看布尔值 >> 返回的内容。 ifFalse：真正接收者的方法...
Everything relevant has already been sayd, but just for your amusement:
As already told,
is the one and single message #'ifTrue:ifFalse:' with 2 args sent to rcvr. The value of that expression is the one from that message send.
In contrast:
is a cascade of 2 sequential messages (#'ifTrue:' and #'ifFalse:'), each with 1 arg sent to rcvr. The value of the expression is the one returned from the last send.
Now the funny thing is that booleans do understand ifTrue: / ifFalse: (each with 1 arg),
so your code works for the side effect (evaluating those blocks), but not for its value.
This means that:
generates the same output as:
but:
will generate different values in msg than:
depending on the values of a and b. Try (a b)=(1 2) vs. (a b)=(2 1)...
The problem of many Smalltalk beginners is that they think of ifXXX: as syntax, where it is actually a message send which generates value. Also, the semi is not a statement separator as in many previously learned languages, but a sequencing message send construct.
A bad trap for beginners, because the code seems to work for some particular value combinations, whereas it generates funny results for others.
Let's hope your unit tests cover these ;-)
edit: to see where the bad value comes from, take a look at what is returned by the Boolean >> ifFalse: method for a true receiver...