NameError.html

---
title: NameError
layout: default
---
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            <span>Ruby on Rails 8.0.0</span><br />
        
        <div class="type">Class</div>
        <h1>
            NameError
            
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                    <a href="Object.html">Object</a>
                    
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        <ul class="files">
            
            <li><a href="../files/activesupport/lib/active_support/core_ext/name_error_rb.html">activesupport/lib/active_support/core_ext/name_error.rb</a></li>
            
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        <div id="content">
  

  

  
  


  

  
    <h2 id="methods">Methods</h2>
    <ul>
      
        <li>
          <a href="#method-i-missing_name">missing_name</a>
        </li>
      
        <li>
          <a href="#method-i-missing_name-3F">missing_name?</a>
        </li>
      
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    <!-- Methods -->
    
    
      <h2 id="instance-public-methods">Instance Public methods</h2>
      
        <div class="method">
          <h3 id="method-i-missing_name">
            
              missing_name()
            
          </h3>

          
            <div class="description">
              <p>Extract the name of the missing constant from the exception message.</p>

<pre><code>begin
  HelloWorld
rescue NameError =&gt; e
  e.missing_name
end
# =&gt; &quot;HelloWorld&quot;
</code></pre>
            </div>
          

          

          

          
          
            <details class="method__source">
              <summary>
                <span class="label">📝 Source code</span>
              </summary>

              <pre><code class="ruby"># File activesupport/lib/active_support/core_ext/name_error.rb, line 12
  def missing_name
    # Since ruby v2.3.0 `did_you_mean` gem is loaded by default.
    # It extends NameError#message with spell corrections which are SLOW.
    # We should use original_message message instead.
    message = respond_to?(:original_message) ? original_message : self.message
    return unless message.start_with?(&quot;uninitialized constant &quot;)

    receiver = begin
      self.receiver
    rescue ArgumentError
      nil
    end

    if receiver == Object
      name.to_s
    elsif receiver
      &quot;#{real_mod_name(receiver)}::#{self.name}&quot;
    else
      if match = message.match(/((::)?([A-Z]\w*)(::[A-Z]\w*)*)$/)
        match[1]
      end
    end
  end</code></pre>
              
                <a href="https://github.com/rails/rails/blob/dd8f7185faeca6ee968a6e9367f6d8601a83b8db/activesupport/lib/active_support/core_ext/name_error.rb#L12" target="_blank" class="github_url">🔎 See on GitHub</a>
              
            </details>
          
        </div>
        
        <div class="method">
          <h3 id="method-i-missing_name-3F">
            
              missing_name?(name)
            
          </h3>

          
            <div class="description">
              <p>Was this exception raised because the given name was missing?</p>

<pre><code>begin
  HelloWorld
rescue NameError =&gt; e
  e.missing_name?(&quot;HelloWorld&quot;)
end
# =&gt; true
</code></pre>
            </div>
          

          

          

          
          
            <details class="method__source">
              <summary>
                <span class="label">📝 Source code</span>
              </summary>

              <pre><code class="ruby"># File activesupport/lib/active_support/core_ext/name_error.rb, line 44
  def missing_name?(name)
    if name.is_a? Symbol
      self.name == name
    else
      missing_name == name.to_s
    end
  end</code></pre>
              
                <a href="https://github.com/rails/rails/blob/dd8f7185faeca6ee968a6e9367f6d8601a83b8db/activesupport/lib/active_support/core_ext/name_error.rb#L44" target="_blank" class="github_url">🔎 See on GitHub</a>
              
            </details>
          
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