不同类型的评估关键字VAR [英] Different types evaluated for keyword var

问题描述

我有以下的code，旨在推断由编译器分配给 VAR 关键字类型2个街区。

I have following 2 blocks of code which aims to infer the type assigned to var keyword by the compiler.

var b = 0x80000000 - 0x1;
Console.WriteLine("b: {0}", b);
Console.WriteLine("b.GetType()={0}", b.GetType());

uint val1 = 0x80000000;
int val2 = 0x1;
var c = val1 - val2;
Console.WriteLine("c: {0}", c);
Console.WriteLine("c.GetType(): {0}", c.GetType());

---

输出：

  b: 2147483647                   //Result of UInt32-Int32
                                  //(as compiler assigns datatype in the
                                  //order of int, uint, long and ulong)
  b.GetType()=System.UInt32       //OK

  c: 2147483647                   //Uint32-Int32                               
  c.GetType(): System.Int64       //Not Understood, why not UInt32 ?

如果变种b 和 VARç几乎相同initialization-其中 VARç甚至明确的，那么为什么它会出现意想不到的数据类型System.Int64？

If var b and var c have almost same initialization- where var c is even explicit, then why does it give unexpected data-type System.Int64 ?

推荐答案

由于

变种B = 0x80000000的 - 为0x1;

时，已经计算。通过优化

is already Computed. by Optimizations

但

var val1 = 0x80000000;
var val2 = 0x1;
var c = val1 - val2;

不计算呢。和编译器猜测， VAL1 和 val2的可后来改...

is Not computed yet. and compiler guess that the val1 and val2 may be changed later...

const uint val1 = 0x80000000;
const int val2 = 0x1;
var c = val1 - val2;

C 是 UInt32的现在，因为编译器计算它，并知道resault。

c is UInt32 now because compiler compute it and knows the resault.

由于 VAL1 和 val2的为常数，编译器知道，他们不会得到改变。所以没有必要的Int64 更多

Because val1 and val2 are constant and Compiler knows that they will not get changed. so there is no need for Int64 any more

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