问题
I practicing in swift\'s playground and I couldn\'t figure out why swift is too specific about where programmer should provide spaces and where not. I asked this question on many sites and chatrooms but didn\'t got any answer.
var j: Int = 34 // Right
var j:Int=23 //Wrong
Also, In class
self.variable-= 5 //Wrong. Error: Consecutive statements must be followed by ;
self.variable-=5 // Right
self.variable -= 5 // Right
;
Even this \":\" creates some issues with spaces sometimes.
I think spaces should have absolutely no effect on the code. It\'s usually just for a programmer\'s benefit. It just makes the code more readable nothing else. What\'s the best resource to read all swift rules about spaces.
回答1:
Answer to the second part of your question can be found here swift docs
The whitespace around an operator is used to determine whether an operator is used as a prefix operator, a postfix operator, or a binary operator. This behavior is summarized in the following rules:
If an operator has whitespace around both sides or around neither side, it is treated as a binary operator. As an example, the + operator in a+b and a + b is treated as a binary operator.
If an operator has whitespace on the left side only, it is treated as a prefix unary operator. As an example, the ++ operator in a ++b is treated as a prefix unary operator.
If an operator has whitespace on the right side only, it is treated as a postfix unary operator. As an example, the ++ operator in a++ b is treated as a postfix unary operator.
If an operator has no whitespace on the left but is followed immediately by a dot (.), it is treated as a postfix unary operator. As an example, the ++ operator in a++.b is treated as a postfix unary operator (a++ .b rather than a ++ .b).
etc... (read the docs for more on this)
As for the first part of your question, I didn't see any issue with either way of declaring the variables.
var j: Int = 34
var j:Int=23
The only issue with that provided code is that you declare j twice in the same scope. Try changing one of the j's to an x or y or something else.
If you were wondering about
var j:Int =10
or
var j:Int= 10
look at the rules above. = is an operator so if you were to do either of those, it would be treated as prefix or postfix, and you would get the error that prefix/postfix = is reserved
These rules are important due to the existence of operators such as the unary plus and unary minus operators. The compiler needs to be able to distinguish between a binary plus and a unary plus operator. List of operators
来源：https://stackoverflow.com/questions/31301715/what-are-the-rules-for-spaces-in-swift