C# 作用域问题

Question

考虑以下代码示例:

                         // line #
{                        // 1
                         // 2
    {                    // 3
        double test = 0; // 4
    }                    // 5
                         // 6  
    double test = 0;     // 7
}                        // 8 

这给出了错误

A local variable named 'test' cannot be declared in this scope because it would give a different meaning to 'test', which is already used in a 'child' scope to denote something else

但我不明白为什么？外部测试变量从第 7 行开始而不是第 2 行，那么在第 4 行声明第二个名为 test 的变量的范围在第 5 行结束的问题在哪里？

Answer 1

变量在它们被声明的 block 范围内，它们在哪一行并不重要。

了解 scopes在 C# 语言规范中。

来自规范:

The scope of a local variable declared in a local-variable-declaration (Section 8.5.1) is the block in which the declaration occurs.

和:

Scopes can be nested, and an inner scope may redeclare the meaning of a name from an outer scope. (This does not, however, remove the restriction imposed by Section 3.3 that within a nested block it is not possible to declare a local variable with the same name as a local variable in an enclosing block.)