blocks|key|2110637|text|它被称为“条件分支是表达式”或“语句/表达式划分的死亡”。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2110638|请参阅Conditional+If+Expressions|offset|length|2110639|2110640|许多语言都支持if表达式，它类似于if语句，但返回一个值作为结果。因此，它们是真的表达式(计算结果为一个值)，而不是语句(只执行一个操作)。|blockquote|2110641|2110642|也就是说，if+(expr)+{+...+}是语言语法中的表达式(可以是表达式或语句，取决于上下文)，就像?:是C、C#或Java等语言中的表达式一样。|style|CODE|2110643|这种形式在函数式编程语言中很常见(避免了副作用)+--然而，它本身并不是“函数式编程”，而是存在于接受/允许“类似函数式语法”的其他语言中，同时仍然使用严重的副作用和其他范例(例如Ruby)。|2110644|一些语言，如Perl，允许模拟这种行为。也就是说，$x+=+eval+{+if+(true)+{+"hello+world!"+}+else+{+"goodbye"+}+};+print+$x将显示"hello+world!“因为eval表达式的计算结果是内部计算的最后一个值，即使if语法结果本身不是一个表达式。($x+=+if+...在Perl中是一个语法错误)。|2110645|祝你编码愉快。|2110646|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Conditional_%2528programming%2529#If_expressions^0|0|3|Q|0|0|0|0|0|5|H|1H|2|0|0|P|1Z|3X|2|4E|B|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|13|8|@]|9|@$D|14|E|15|1|16]]|A|$]]|$1|F|3|-4|5|6|7|17|8|@]|9|@]|A|$]]|$1|G|3|H|5|I|7|18|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|19|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|1A|8|@$D|1B|E|1C|M|N]|$D|1D|E|1E|M|N]]|9|@]|A|$]]|$1|O|3|P|5|6|7|1F|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1G|8|@$D|1H|E|1I|M|N]|$D|1J|E|1K|M|N]|$D|1L|E|1M|M|N]]|9|@]|A|$]]|$1|S|3|T|5|6|7|1N|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|1O|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]]]

It is called "conditional-branches-are-expressions" or "death to the statement/expression divide".

See <a href="http://en.wikipedia.org/wiki/Conditional_%28programming%29#If_expressions" rel="nofollow">Conditional If Expressions</a>:

<blockquote>
 <blockquote>
 Many languages support if expressions, which are similar to if statements, but return a value as a result. Thus, they are true expressions (which evaluate to a value), not statements (which just perform an action).
 </blockquote>
</blockquote>

That is, <code>if (expr) { ... }</code> is an expression (could possible be an expression or a statement depending upon context) in the language grammar just as <code>?:</code> is an expression in languages like C, C# or Java.

This form is common in functional programming languages (which eschew side-effects) -- however, it is not "functional programming" per se and exists in other language that accept/allow a "functional like syntax" while still utilizing heavy side-effects and other paradigms (e.g. Ruby).

Some languages like Perl allow this behavior to be simulated. That is, <code>$x = eval { if (true) { "hello world!" } else { "goodbye" } }; print $x</code> will display "hello world!" because the eval expression evaluates to the last value evaluated inside even though the <code>if</code> grammar production itself is not an expression. (<code>$x = if ...</code> is a syntax error in Perl).

Happy coding.

blocks|key|1518543|text|它是一个三元条件。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1518544|在C中，你可以使用，例如：|1518545|printf("Debug?+%25s\n",+debug?"yes":"no");|code-block|syntax|javascript|1518546|编辑：|1518547|复合语句列表可以在C中作为表达式求值。最后一条语句应该是一个表达式，并且整个复合语句都要用大括号括起来。|1518548|例如：|1518549|#include+<stdio.h>

int+main(void)
{
++++int+a=0,+b=1;

++++a=({
++++++++++++printf("testing+compound+statement\n");
++++++++++++if(b==a)
++++++++++++++++printf("equals\n");
++++++++++++b%2B1;
++++++++});

++++printf("a=%25d\n",+a);
++++return+0;
}|1518550|因此，您正在执行的特征的名称是将复合语句赋值给(本地)变量。现在我认为这对你有更多的帮助。如需更多信息，请访问以下网址：http://www.chemie.fu-berlin.de/chemnet/use/info/gcc/gcc_8.html|offset|length|1518551|保重，贝科。|1518552|PS。这个例子在你的问题的上下文中更有意义：|1518553|a=({
++++++++int+c;
++++++++if(b==a)
++++++++++++c=b%2B1;
++++++++else
++++++++++++c=a-1;
++++++++c;
++++});|1518554|entityMap|0|LINK|mutability|MUTABLE|url|http://www.chemie.fu-berlin.de/chemnet/use/info/gcc/gcc_8.html^0|0|0|0|0|0|0|0|1O|1Q|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|18|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|19|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|1A|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|1B|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|1C|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|1D|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|1E|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|1F|8|@]|9|@$S|1G|T|1H|1|1I]]|A|$]]|$1|U|3|V|5|6|7|1J|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|1K|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|F|7|1L|8|@]|9|@]|A|$G|H]]|$1|10|3|-4|5|6|7|1M|8|@]|9|@]|A|$]]]|11|$12|$5|13|14|15|A|$16|17]]]]

It is a ternary conditional.

In C you can use, for example:

<pre><code>printf("Debug? %s\n", debug?"yes":"no");
</code></pre>

Edited:

A compound statement list can be evaluated as a expression in C. The last statement should be a expression and the whole compound statement surrounded by braces.

For example:

<pre><code>#include &lt;stdio.h&gt;

int main(void)
{
 int a=0, b=1;

 a=({
 printf("testing compound statement\n");
 if(b==a)
 printf("equals\n");
 b+1;
 });

 printf("a=%d\n", a);
 return 0;
}
</code></pre>

So the name of the characteristic you are doing is assigning to a (local) variable a compound statement. Now I think this helps you a little bit more. For more, please visit this source:
<a href="http://www.chemie.fu-berlin.de/chemnet/use/info/gcc/gcc_8.html" rel="nofollow">http://www.chemie.fu-berlin.de/chemnet/use/info/gcc/gcc_8.html</a>

Take care,
Beco.

PS. This example makes more sense in the context of your question:

<pre><code>a=({
 int c;
 if(b==a)
 c=b+1;
 else
 c=a-1;
 c;
 });
</code></pre>

blocks|key|2110677|text|回答你的另一个问题：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2110678|2110679|在诸如C#这样的静态类型语言中也可以实现吗？|blockquote|2110680|2110681|2110682|这是一种语言支持的东西吗？不是的。它能实现吗？有点。|2110683|C#+--像C%2B%2B、Java以及其他诸如此类的东西--有表达式和语句。if-then和switch-case等语句不返回值，因此不能用作表达式。另外，顺便提一下，您的示例将myValue赋值给字符串或整数，这是C#不能做的，因为它是强类型的。您要么使用object+myValue，然后接受转换和装箱成本，要么使用var+myValue+(它仍然是静态类型的，只是推断出来的)，或者其他一些奇怪的聪明方法。|offset|length|style|CODE|2110684|无论如何，如果if-then是一条语句，那么如何在C#中做到这一点呢？您必须构建一个方法来实现if-then-else的目标。您可以使用静态方法作为bools的扩展，以Smalltalk的方式进行建模：|2110685|公共静态T值(此布尔值，操作doThen，操作doElse+){if(IfTrue)doThen+doThen()；else+return+doElse()；}|2110686|要使用它，您应该这样做：|2110687|var+myVal+=+(6+<+7).IfTrue(()+=>+return+"Less+than",+()+=>+return+"Greater+than");|code-block|syntax|javascript|2110688|2110689|免责声明:我没有测试过这些，所以它可能由于拼写错误而不太有效，但我认为原则是正确的。|unordered-list-item|2110690|2110691|新的IfTrue()函数检查它所附加的布尔值，并执行传递给它的两个委托中的一个。它们必须具有相同的返回类型，并且都不接受参数(使用闭包，所以这无关紧要)。|2110692|现在，你应该这样做吗？不，几乎可以肯定不是。这不是正确的C#方式，所以它令人困惑，而且它的效率比使用if-then低得多。您正在用一条IL指令来换取一堆复杂的类和方法调用，.NET将在幕后构建这些类和方法调用来支持这一点。|2110693|entityMap^0|0|0|0|0|0|0|2E|7|3I|E|4D|B|0|7|7|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1B|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|1D|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]|$1|G|3|-4|5|6|7|1F|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|1G|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|1H|8|@$L|1I|M|1J|N|O]|$L|1K|M|1L|N|O]|$L|1M|M|1N|N|O]]|9|@]|A|$]]|$1|P|3|Q|5|6|7|1O|8|@$L|1P|M|1Q|N|O]]|9|@]|A|$]]|$1|R|3|S|5|6|7|1R|8|@]|9|@]|A|$]]|$1|T|3|U|5|6|7|1S|8|@]|9|@]|A|$]]|$1|V|3|W|5|X|7|1T|8|@]|9|@]|A|$Y|Z]]|$1|10|3|-4|5|6|7|1U|8|@]|9|@]|A|$]]|$1|11|3|12|5|13|7|1V|8|@]|9|@]|A|$]]|$1|14|3|-4|5|6|7|1W|8|@]|9|@]|A|$]]|$1|15|3|16|5|6|7|1X|8|@]|9|@]|A|$]]|$1|17|3|18|5|6|7|1Y|8|@]|9|@]|A|$]]|$1|19|3|-4|5|6|7|1Z|8|@]|9|@]|A|$]]]|1A|$]]

To answer your other question:

<blockquote>
 Can this also be achieved in staticly typed languages such as C#?
</blockquote>

Is it a thing the language supports? No. Can it be achieved? Kind of.

C# --like C++, Java, and all that ilk-- has expressions and statements. Statements, like if-then and switch-case, don't return values and there fore can't be used as expressions. Also, as a slight aside, your example assigns <code>myValue</code> to either a string or an integer, which C# can't do because it is strongly typed. You'd either have to use <code>object myValue</code> and then accept the casting and boxing costs, use <code>var myValue</code> (which is still static typed, just inferred), or some other bizarre cleverness.

Anyway, so if <code>if-then</code> is a statement, how do you do that in C#? You'd have to build a method to accomplish the goal of if-then-else. You could use a static method as an extension to bools, to model the Smalltalk way of doing it:

public static T IfTrue(this bool value, Action doThen, Action doElse )
 {
 if(value)
 return doThen();
 else
 return doElse();
 }

To use this, you'd do something like

<pre><code>var myVal = (6 &lt; 7).IfTrue(() =&gt; return "Less than", () =&gt; return "Greater than");
</code></pre>

<ul>
<li>Disclaimer: I tested none of that, so it may not quite work due to typos, but I think the principle is correct.</li>
</ul>

The new IfTrue() function checks the boolean it is attached to and executes one of two delegates passed into it. They must have the same return type, and neither accepts arguments (use closures, so it won't matter). 

Now, should you do that? No, almost certainly not. Its not the proper C# way of doing things so it's confusing, and its much less efficient than using an if-then. You're trading off something like 1 IL instruction for a complex mess of classes and method calls that .NET will build behind the scenes to support that.

blocks|key|1518639|text|除了返回分支中最后一个表达式的值之外，很可能(取决于语言)将myValue赋值给一个匿名函数--或者在Smalltalk+/+Ruby中，code+blocks|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1518640|1518641|代码块(匿名函数)可以表示为文字值(这是一个对象，因为所有的值都是对象)。|blockquote|1518642|1518643|1518644|在本例中，由于myValue实际上指向一个仅在使用myValue时调用的函数，因此该语言可能将它们实现为closures，这最初是函数式语言的一个特性。|1518645|因为闭包是具有自由变量的一流函数，所以closures+exist+in+C#。但是，隐式返回不会发生；在C#中，它们只是匿名委托！考虑一下：|1518646|Func<Object>+myValue+=+delegate()+
{
++++if+(this.IsValidObject)
++++{
++++++++UpdateGraph();
++++++++UpdateCount();
++++++++return+this.Name;
++++}
++++else
++++{
++++++++Debug.Log+(Exceptions.UninitializedObject);
++++++++return+3;
++++}
};|code-block|syntax|javascript|1518647|这也可以在C#中使用lambda表达式来完成：|1518648|Func<Object>+myValue+=+()+=>+
{
++++if+(this.IsValidObject)+{+...+}
++++else++++++++++++++++++++{+...+}
};|1518649|我知道你的问题是关于隐式返回值的，但我想说明的是，这里不仅仅是“条件分支是表达式”。|1518650|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Smalltalk#Code_blocks|1|http://en.wikipedia.org/wiki/Closure_%2528computer_science%2529|2|http://www.codethinked.com/c-closures-explained^0|U|7|1X|B|0|0|0|0|0|0|7|7|P|7|1G|8|1|0|J|K|2|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1C|8|@$9|1D|A|1E|B|C]]|D|@$9|1F|A|1G|1|1H]]|E|$]]|$1|F|3|-4|5|6|7|1I|8|@]|D|@]|E|$]]|$1|G|3|H|5|I|7|1J|8|@]|D|@]|E|$]]|$1|J|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]|$1|K|3|-4|5|6|7|1L|8|@]|D|@]|E|$]]|$1|L|3|M|5|6|7|1M|8|@$9|1N|A|1O|B|C]|$9|1P|A|1Q|B|C]]|D|@$9|1R|A|1S|1|1T]]|E|$]]|$1|N|3|O|5|6|7|1U|8|@]|D|@$9|1V|A|1W|1|1X]]|E|$]]|$1|P|3|Q|5|R|7|1Y|8|@]|D|@]|E|$S|T]]|$1|U|3|V|5|6|7|1Z|8|@]|D|@]|E|$]]|$1|W|3|X|5|R|7|20|8|@]|D|@]|E|$S|T]]|$1|Y|3|Z|5|6|7|21|8|@]|D|@]|E|$]]|$1|10|3|-4|5|6|7|22|8|@]|D|@]|E|$]]]|11|$12|$5|13|14|15|E|$16|17]]|18|$5|13|14|15|E|$16|19]]|1A|$5|13|14|15|E|$16|1B]]]]

In addition to returning the value of the last expression in a branch, it's likely (depending on the language) that <code>myValue</code> is being assigned to an anonymous function -- or in Smalltalk / Ruby, <a href="http://en.wikipedia.org/wiki/Smalltalk#Code_blocks" rel="nofollow">code blocks</a>:

<blockquote>
 A block of code (an anonymous function) can be expressed as a literal value (which is an object, since all values are objects.)
</blockquote>

In this case, since <code>myValue</code> is actually pointing to a function that gets invoked only when <code>myValue</code> is used, the language probably implements them as <a href="http://en.wikipedia.org/wiki/Closure_%28computer_science%29" rel="nofollow">closures</a>, which are originally a feature of functional languages.

Because closures are first-class functions with free variables, <a href="http://www.codethinked.com/c-closures-explained" rel="nofollow">closures exist in C#</a>. However, the implicit return does not occur; in C# they're simply anonymous delegates! Consider:

<pre><code>Func&lt;Object&gt; myValue = delegate() 
{
 if (this.IsValidObject)
 {
 UpdateGraph();
 UpdateCount();
 return this.Name;
 }
 else
 {
 Debug.Log (Exceptions.UninitializedObject);
 return 3;
 }
};
</code></pre>

This can also be done in C# using lambda expressions:

<pre><code>Func&lt;Object&gt; myValue = () =&gt; 
{
 if (this.IsValidObject) { ... }
 else { ... }
};
</code></pre>

I realize your question is asking about the implicit return value, but I am trying to illustrate that there is more than just "conditional branches are expressions" going on here.

blocks|key|5187991|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5187992|这也可以在静态类型的语言中实现吗？|blockquote|5187993|5187994|5187995|当然，可以静态地严格检查所涉及的表达式的类型。在"if-as-expression“方法中似乎没有任何依赖于动态类型的东西。|5187996|例如，Haskell--一种具有丰富类型系统的严格静态类型语言：|5187997|$+ghci
Prelude>+let+x+=+if+True+then+"a"+else+"b"+in+x
"a"|code-block|syntax|javascript|5187998|(示例表达式可以更简单，我只是想反映您问题中的赋值，但演示该功能的表达式可以更简单：|5187999|Prelude>+if+True+then+"a"+else+"b"
"a"|5188000|。)|5188001|entityMap^0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|-4|4|5|6|W|7|@]|8|@]|9|$]]|$1|A|3|B|4|C|6|X|7|@]|8|@]|9|$]]|$1|D|3|-4|4|5|6|Y|7|@]|8|@]|9|$]]|$1|E|3|-4|4|5|6|Z|7|@]|8|@]|9|$]]|$1|F|3|G|4|5|6|10|7|@]|8|@]|9|$]]|$1|H|3|I|4|5|6|11|7|@]|8|@]|9|$]]|$1|J|3|K|4|L|6|12|7|@]|8|@]|9|$M|N]]|$1|O|3|P|4|5|6|13|7|@]|8|@]|9|$]]|$1|Q|3|R|4|L|6|14|7|@]|8|@]|9|$M|N]]|$1|S|3|T|4|5|6|15|7|@]|8|@]|9|$]]|$1|U|3|-4|4|5|6|16|7|@]|8|@]|9|$]]]|V|$]]

<blockquote>
 Can this also be achieved in staticly
 typed languages?
</blockquote>

Sure, the types of the involved expressions can be statically and strictly checked. There seems to be nothing dependent on dynamic typing in the "if-as-expression" approach.

For example, Haskell--a strict statically typed language with a rich system of types:



<pre class="lang-hs prettyprint-override"><code>$ ghci
Prelude&gt; let x = if True then "a" else "b" in x
"a"
</code></pre>

(the example expression could be simpler, I just wanted to reflect the assignment from your question, but the expression to demonstrate the feature could be simlpler:



<pre class="lang-hs prettyprint-override"><code>Prelude&gt; if True then "a" else "b"
"a"
</code></pre>

.)

In some dynamic languages I have seen this kind of syntax:

<pre><code>myValue = if (this.IsValidObject)
{
 UpdateGraph();
 UpdateCount();
 this.Name;
}
else
{
 Debug.Log (Exceptions.UninitializedObject);
 3;
}
</code></pre>

Basically being able to return the last statement in a branch as the return value for a variable, not necessarily only for method returns, but they could be achieved as well.

What's the name of this feature?

Can this also be achieved in staticly typed languages such as C#? I know C# has ternary operator, but I mean using if statements, switch statements as shown above.

What's the name of this programming feature?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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在一些动态语言中，我见过这样的语法：myValue = if (this.IsValidObject){    UpdateGraph();    UpdateCount();    this.Name;}else{    Debug.Log (Exceptions.UninitializedObject);    3...

问这个编程功能的名称是什么？
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问这个编程功能的名称是什么？EN