如何在proc之外访问变量 [英] How do I access a variable outside of a proc

问题描述

我正在尝试围绕Tcl变量作用域，但是我一直坚持我认为这是一个简单的概念:如何访问在proc之外定义的变量，但是我没有明确传递给proc?

I'm trying to wrap my head around Tcl variable scopes, but I'm stuck on what I thought would be a simple concept: how can I access a variable that I've defined outside of my proc, but that I do not explicitly pass to the proc?

我试图避免设置一堆全局变量，而只访问我在特定名称空间中定义的变量.我需要在下面的代码中添加些什么，以便proc可以访问变量 a ，而该变量显然不在proc的范围内?

I'm trying to avoid setting a bunch of global variables, and only access variables that I define within a particular namespace. What do I need to add to my code below so that the proc can access the variable a, which is obviously not in the scope of the proc?

set a apples
proc myList {b c} {
   puts [concat $a $b $c]
}

推荐答案

您可以使用 upvar :

You can use upvar:

set a apples
proc myList {b c} {
    upvar a a
    puts [concat $a $b $c]
}

或者，稍微扩展一下示例以显示"source"变量不必在全局范围内存在:

Or, expanding the example a bit to show the "source" variable does not have to exist in the global scope:

proc p1 {} { set a 10; p2 }
proc p2 {} { upvar 1 a b; puts "in p2, value is $b" }
p1

输出

in p2, value is 10

---

如果在命名空间中定义了 a ，则可以使用

---

If a was defined in a namespace, you can use variable:

namespace eval foo {
    set a apples
    # OR
    # variable a apples
}

proc foo::myList {b c} {
    variable a
    puts [concat $a $b $c]
}

或者如果 a 是在全局范围内创建的，您仍然可以使用 :: 来访问它而无需 global 函数(我ll参考关于此问题的问题):

Or if a was created in the global scope, you can still access it without the global function, using :: (I'll reference this SO question for this one):

proc myList {b c} {
    puts [concat $::a $b $c]
}

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