C# 结构:未分配的局部变量? [英] C# Structs: Unassigned local variable?

问题描述

来自文档:

与类不同，结构体可以在不使用 new 运算符的情况下进行实例化.

Unlike classes, structs can be instantiated without using a new operator.

那为什么我会收到这个错误:

So why am I getting this error:

使用未赋值的局部变量'x'

Use of unassigned local variable 'x'

当我尝试这样做时?

        Vec2 x;
        x.X = det * (a22 * b.X - a12 * b.Y);
        x.Y = det * (a11 * b.Y - a21 * b.X);

其中 Vec2 x 是结构体?

推荐答案

嗯，X 和 Y 是属性(而不是字段)吗?如果是这样，那就是问题所在.在 x 中的所有字段都被明确赋值之前，你不能调用任何方法或属性.

Well, are X and Y properties (rather than fields)? If so, that's the problem. Until all the fields within x are definitely assigned, you can't call any methods or properties.

例如:

public struct Foo
{
    public int x;
    public int X { get { return x; } set { x = value; } }
}

class Program
{
    static void Main(string[] args)
    {
        Foo a;
        a.x = 10; // Valid

        Foo b;
        b.X = 10; // Invalid
    }
}

Vec2 是你自己的类型吗?您可以访问所涉及的字段，还是只能访问属性?

Is Vec2 your own type? Do you have access to the fields involved, or only the properties?

如果它是您自己的类型，我会强烈敦促您尝试坚持不可变结构.我知道托管 DirectX 有一些可变结构来尽可能接近最佳性能，但这是以这种奇怪情况为代价的 - 说实话，更糟糕的是.

If it's your own type, I would strongly urge you to try to stick to immutable structs. I know managed DirectX has some mutable structs for getting as close to optimal performance as possible, but that's at the cost of strange situations like this - and much worse, to be honest.

我个人会给结构一个带 X 和 Y 的构造函数:

I would personally give the struct a constructor taking X and Y:

 Vec2 x = new Vec2(det * (a22 * b.X - a12 * b.Y),
                   det * (a11 * b.Y - a21 * b.X));

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