title: Why default argument cannot be specified for an explicit template specialization?
body: <p>The below code couldn't pass the compilation, what's the consideration for this compiler error?</p>
  
  <pre><code>template&lt;class T&gt; void f(T t) {};
  
  template&lt;&gt; void f&lt;char&gt;(char c = 'a') {}
  </code></pre>
  
  <p>Error message: Default arguments are not allowed on an explicit specialization of a function template</p>