title: C# lambda expressions without variable / parameter declaration?
body: <p>What's it called when a method that takes a lambda expression as the parameter, such as <a href="https://msdn.microsoft.com/en-us/library/bb534803%28v=vs.110%29.aspx" rel="nofollow noreferrer">Enumerable.Where</a>, is invoked without actually declaring a variable or method parameter in the expression?</p>
  
  <p>For example, I'm familiar with this lambda expression syntax:</p>
  
  <pre><code>public string GetDigits(string input)
  {
      return new String(input.Where(i =&gt; Char.IsDigit(i)).ToArray());
  }
  </code></pre>
  
  <p>However, I was surprised to <a href="https://stackoverflow.com/a/844479/12484">find out</a> that this can also be written as:</p>
  
  <pre><code>public string GetDigits(string input)
  {
      return new String(input.Where(Char.IsDigit).ToArray());
  }
  </code></pre>
  
  <p>What's going on in that second snippet, where the Char.IsDigit() method is (apparently) being called with an implicit parameter?  What is this syntax called?</p>