没有隐式int - ＆GT;三元声明总之转换 [英] No implicit int -> short conversion in ternary statement

问题描述

short s;
s = (EitherTrueOrFalse()) ? 0 : 1;

这失败：

错误CS0266：无法隐
  转换类型'诠释'到'短'。一个
  显式转换存在（是你
  缺少强制转换？）

error CS0266: Cannot implicitly convert type 'int' to 'short'. An explicit conversion exists (are you missing a cast?)

谁能解释这是为什么？我能想到的唯一的事情就是编译器不会再看第二值，不知道这两者之间的范围内，我写了类似的情况。

Can anyone explain why this is so? The only thing I can think of is that the compiler doesn't look at the second value and doesn't know the range between the two, in the case I wrote something like

short s;
s = (EitherTrueOrFalse()) ? 0 : 65000;

正确？
唯一的解决方法是用一个丑陋的投？

Correct? The only fix is with an ugly cast?

此外，似乎C＃不具有用于短类型的类型后缀。这是一个pretty坟墓监督海事组织。否则，将一直在一个解决方案...

Also, it seems C# does not have a type suffix for the short type. That's a pretty grave oversight IMO. Otherwise, that would've been a solution...

推荐答案

编译器有从的恒的前pression各种基本类型的隐式转换（只要该值范围内适当的范围内），但这里的前pression不是恒定的 - 它只是一个int前pression。这是pretty一样一样的：

The compiler has an implicit conversion from a constant expression to various primitive types (so long as the value is within the appropriate range), but here the expression isn't constant - it's just an int expression. It's pretty much the same as:

short s;
s = CallSomeMethodReturningInt32();

至于编译器而言。

as far as the compiler is concerned.

有两种选择 - 你可以施放整个前pression，或每次投后两个操作数：

There are two options - you could cast the whole expression, or cast each of the latter two operands:

short s = (EitherTrueOrFalse()) ? (short) 0 : (short) 1;

使整个前pression键入短。在这种特殊情况下，这是一个遗憾的是，没有一个数字文字后缀以显式声明短文字。显然，语言的设计者确实考虑这一点，但觉得这是一个比较罕见的情况。 （我想我可能会同意。）

to make the overall expression type short. In this particular case, it's a pity that there isn't a numeric literal suffix to explicitly declare a short literal. Apparently the language designers did consider this, but felt it was a relatively rare situation. (I think I'd probably agree.)

有关隐式转换不变的部分是从C＃3.0规范6.1.8节：

The part about implicit constant conversions is from the C# 3.0 spec section 6.1.8:

6.1.8隐定前pression转换

这是隐定
  前pression转换允许的
  下列转换：

An implicit constant expression conversion permits the following conversions:

  
• A 恒前pression 的（§7.18）型
     INT 可转换为类型为sbyte，
    字节，短， USHORT ， UINT 或 ULONG ，
    所提供的价值
    的恒前pression 的距离
    在目标类型的范围。

  
• 系统
    的恒前pression 的类型长 CAN
    被转换成键入 ULONG ，提供
    的值的恒前pression 的
    是不是消极的。

  

• A constant-expression (§7.18) of type int can be converted to type sbyte, byte, short, ushort, uint, or ulong, provided the value of the constant-expression is within the range of the destination type.
• A constant-expression of type long can be converted to type ulong, provided the value of the constant-expression is not negative.

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