<p></p> <p>Switch表達(dá)式在C#中是一種比傳統(tǒng)switch語句更簡(jiǎn)潔、更易讀的處理多個(gè)條件的方式。它於C# 8.0引入，適用於基於條件賦值的場(chǎng)景，無需編寫大量case和break語句。其基本語法使用=>操作符返回每個(gè)匹配模式的結(jié)果，例如通過dayOfWeek switch來判斷星期並返回對(duì)應(yīng)的字符串描述。使用_符號(hào)可作為默認(rèn)情況的處理。 1. 它支持通過or關(guān)鍵字匹配多個(gè)值，使代碼更簡(jiǎn)潔；2. 可進(jìn)行類型匹配，根據(jù)輸入類型執(zhí)行不同邏輯；3. C# 9 支持關(guān)係模式匹配，如使用等操作符判斷數(shù)值範(fàn)圍；4. 建議保持每個(gè)分支簡(jiǎn)短，用於返回值而非複雜邏輯；5. 盡可能替代傳統(tǒng)switch語句以提升代碼整潔度；6. 必要時(shí)記得添加默認(rèn)情況以確保完整性。總之，C# switch表達(dá)式是一個(gè)強(qiáng)大且富有表現(xiàn)力的特性，能簡(jiǎn)化代碼結(jié)構(gòu)並提高可讀性。 </p> <p><img src="/static/imghw/default1.png" data-src="https://img.php.cn/upload/article/000/000/000/175363492366204.jpg" class="lazy" alt="How to use C# switch expressions?"></p> <p> Switch expressions in C# are a more concise and readable way to handle multiple conditions compared to traditional <code>switch</code> statements. They were introduced in C# 8.0 and are especially useful when you want to assign a value based on a condition without writing a lot of <code>case</code> and <code>break</code> statements. </p> <img src="/static/imghw/default1.png" data-src="https://img.php.cn/upload/article/000/000/000/175363492554742.jpg" class="lazy" alt="How to use C# switch expressions?"><hr> <h3 id="Basic-Syntax-and-Usage"> Basic Syntax and Usage</h3> <p> A switch expression evaluates a value and returns a result based on matching patterns. The syntax is clean and uses the <code>=></code> operator to return a value for each case.</p> <p> Here's a simple example: </p> <img src="/static/imghw/default1.png" data-src="https://img.php.cn/upload/article/000/000/000/175363492712401.jpg" class="lazy" alt="How to use C# switch expressions?"><pre class='brush:php;toolbar:false;'> string day = DateTime.Now.DayOfWeek switch { DayOfWeek.Monday => "Start of the workweek", DayOfWeek.Friday => "Almost weekend!", DayOfWeek.Saturday or DayOfWeek.Sunday => "Weekend!", _ => "Midweek" };</pre><ul><li> Each line inside the braces represents a pattern and its corresponding result.</li><li> The <code>_</code> symbol is the discard operator, acting as a default case.</li></ul><p> This is much cleaner than writing a full <code>switch</code> block with <code>case</code> , <code>break</code> , and variable assignments.</p><hr /><h3 id="Matching-Multiple-Values"> Matching Multiple Values</h3><p> You can match multiple values using the <code>or</code> keyword. This helps avoid repetition and keeps your code DRY (Don't Repeat Yourself). </p><img src="/static/imghw/default1.png" data-src="https://img.php.cn/upload/article/000/000/000/175363492867744.png" class="lazy" alt="How to use C# switch expressions?" /><p> For example:</p><pre class='brush:php;toolbar:false;'> string mood = feeling switch { "happy" or "excited" => "Great to hear!", "sad" or "tired" => "Take care!", _ => "Hope you&#39;re doing okay" };</pre><p> This makes it easy to group related cases together without duplicating logic.</p><hr /><h3 id="Using-Patterns-Beyond-Simple-Values"> Using Patterns Beyond Simple Values</h3><p> C# switch expressions support more advanced pattern matching features, such as checking types or relational patterns.</p><h4 id="Type-Matching"> Type Matching</h4><pre class='brush:php;toolbar:false;'> string Describe(object obj) => obj switch { int i => $"An integer: {i}", string s => $"A string: {s}", null => "Nothing", _ => "Unknown type" };</pre><p> This allows you to write logic that behaves differently depending on the type of the input.</p><h4 id="Relational-Patterns-C"> Relational Patterns (C# 9 )</h4><p> You can also use relational operators like <code><</code> , <code>></code> , etc.</p><pre class='brush:php;toolbar:false;'> string GetResult(int score) => score switch { < 60 => "Fail", >= 60 and < 70 => "Pass", >= 70 and < 90 => "Good", _ => "Excellent" };</pre><p> This replaces what used to require <code>if-else if-else</code> chains and makes the logic more compact.</p> <hr> <h3 id="Tips-for-Using-Switch-Expressions-Effectively"> Tips for Using Switch Expressions Effectively</h3> <ul> <li> Keep each case short and focused — switch expressions are best when returning a value, not executing complex logic.</li> <li> Use them when you have multiple discrete values or conditions that map to results.</li> <li> Prefer them over traditional <code>switch</code> statements when possible for cleaner code.</li> <li> Don't forget the default case ( <code>_</code> ) unless you're sure all possible values are covered.</li> </ul> <hr> <p> Overall, C# switch expressions are a powerful and expressive feature that can simplify your code and improve readability. They're especially handy when dealing with enums, strings, or basic conditional mappings. Just remember to keep things clear and logical — don't overdo it with too many nested conditions or complex patterns.基本上就這些。</p>

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