Annonymous functions and foreach usage on event-driven code in julia

Question

I'm currently following Julia for pythonistas notebook by Aurelien Geron (https://github.com/ageron/julia_notebooks) and I'm a bit confused on annonymous functions chapter with the following code:

handlers = []

on_click(handler) = push!(handlers, handler)

click(event) = foreach(handler->handler(event), handlers)

on_click() do event
    println("Mouse clicked at $event")
end

on_click() do event
    println("Beep.")
end

click((x=50, y=20))
click((x=120, y=10))

Mainly I can't see how on_click() gets the event from click(). Can anyone shed some light on it?

Answer 1

可能不明显的是handlers数组是如何填充的，即通过应用on_click()两次。

on_click(handler) = push!(handlers, handler)

定义了一个添加处理程序的函数，而

on_click() do event
    println("Mouse clicked at $event")
end

on_click() do event
    println("Beep.")
end

两次调用这个新定义的函数。在do这个符号揣一点点，但基本上都是这样的语句：

push!(handlers, event -> println("Mouse clicked at $event"))
push!(handlers, event -> println("Beep."))

click()调用when 之后的内容是将提供的元素（例如(x=50, y=29)）传递给使用该foreach构造的所有处理程序。