title: Differences Objective-C const and let Swift in terms of run and compile time
body: <p>I am trying to figure out difference between Objective-C and Swift constant. I just read a tutorial document</p>
  <pre><code>//Objective-C
  const int number = 0;
  //Swift
  let number = 0
  </code></pre>
  <blockquote>
  <p>&quot;A const is a variable initialized at compile time with a value or an expression that must be resolved at compilation time.
  An immutable created with let is a constant determined at runtime. You can initialize it with a static or a dynamic expression. This allows a declaration such as:</p>
  </blockquote>
  <pre><code>let higherNumber = number + 5
  </code></pre>
  <blockquote>
  <p>Note that you can only assign its value once.&quot;</p>
  </blockquote>
  <p>Can someone explain these phrases and deep little dive into to explain why let constant determined at runtime ? I was thinking let is constant and never change.</p>