避免CoffeeScript传递对象引用样式的方法

Question

I'm trying to copy (deep copy specifically) an object in CoffeeScript. Here's the problem:

class Mat
  constructor: ->
    @m00 = 5
    @m01 = 3
  mul: (b) ->
    x1 = @m00
    @m00 = x1 * b.m00
    @m01 = x1 * b.m00

x = new Mat
x.mul(x)
alert x.m00 #25
alert x.m01 #125

So as you can see,

• x1 gets set to @m00
• @m00 changes
• x1 changes with changes made to @m00

How can I instead get the copy to be a new object with the values so that changing the instance's values won't affect it? I am trying to avoid this...

x1 = @m00
y1 = b.m00
@m00 = x1 * y1

EDIT: Another example

  @m00 = b.m00 * copy.m00 + b.m01 * copy.m03 + b.m02 * copy.m06
  @m01 = b.m00 * copy.m01 + b.m01 * copy.m04 + b.m02 * copy.m07
  @m02 = b.m00 * copy.m02 + b.m01 * copy.m05 + b.m02 * copy.m08
  @m03 = b.m03 * copy.m00 + b.m04 * copy.m03 + b.m05 * copy.m06
  @m04 = b.m03 * copy.m01 + b.m04 * copy.m04 + b.m05 * copy.m07
  @m05 = b.m03 * copy.m02 + b.m04 * copy.m05 + b.m05 * copy.m08
  @m06 = b.m06 * copy.m00 + b.m07 * copy.m03 + b.m08 * copy.m06
  @m07 = b.m06 * copy.m01 + b.m07 * copy.m04 + b.m08 * copy.m07
  @m08 = b.m06 * copy.m02 + b.m07 * copy.m05 + b.m08 * copy.m08

Answer 1

I'm still not sure what you're up to, but let's look at what the latest version of "mul" does:

  mul: (b) ->
    x1 = @m00
    @m00 = x1 * b.m00
    @m01 = x1 * b.m00

Your code calls "mul" with "x" as both the context and the parameter ("b"). Thus, the first line of code,

    x1 = @m00

sets local variable "x1" to x.m00 . That's the same as b.m00 , remember.

The next line of code sets x.m00 to the product of the value of "x1" times b.m00 , which if of course the same as x.m00 . Thus, after

    @m00 = x1 * b.m00

the value of x.m00 (and, because "b" and "x" refer to the same object, b.m00 ) is 25 .

The next statement:

    @m01 = x1 * b.m00

sets x.m01 (and b.m01 ) to the product of "x1" and the current value of b.m00 . Well, "x1" is still 5 , because it hasn't been changed. But b.m00 is now 25 because of the previous statement. Thus, the value of x.m01 is set to 125 ( 5 * 25 ).