我想定义和使用一些变量而不影响命名空间。
例如,在 C/C++/Java 中:
{
int i = 42;
...
}
int i = 52; // different variable
在Javascript中:
(function() {
var i = 42;
...
})();
var i = 52; // different variable
i
仅对块或函数范围内的代码可见,并且尚未创建全局命名空间。
有没有办法在 Ruby 中编写等效项?
你可以做与javascript版本几乎相同的操作
lambda do |;x|
x = 42
end.call
puts x #=> NameError
请注意,上述和
lambda do
x = 42
end.call
如果外部作用域中没有局部变量x
则两者的行为相同。 但是,如果有这样的局部变量,那么第二个代码段将可以访问其值,并且更改将影响外部范围,但第一个版本不能执行这些操作中的任何一个。
Ruby 变量默认是局部变量。您可以创建具有各种前缀的其他类型的变量:$
表示全局变量,例如@
,@@
表示类。
i = 52
def a_function
puts i
i = 42
puts i
end
puts i # this prints 52
# but when you call the function
a_function rescue nil # this will raise an error and catch it with rescue, because a_function cannot access
# local variables of the scope where the function is defined
# which is the main object in this case
# so a local variable is local to the scope where it was defined but never
# be accessible from scopes of other functions
# but this is different if we talk about blocks so if you do this
1.times{ puts i }
# it will print 52
# and a block can also change the value of a local variable
1.times{ i = 60 }
puts i # this prints 60
# functions or methods are not closures in ruby, but blocks, in some sense, are
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