Databases
StackOverflow2013
Postsdbo
POWhere and how is the _ (underscore) variable specified?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POWhere and how is the _ (underscore) variable specified?
    primarykey
    data
    text
    <p>Most are aware of <code>_</code>’s special meaning in IRB as a holder for last return value, but that is <em>not</em> what I'm asking about here.</p> <p>Instead, I’m asking about <code>_</code> when used as a variable name in plain-old-Ruby-code. Here it appears to have special behavior, akin to a “don't care variable” (à la <a href="http://www.cse.unsw.edu.au/~billw/prologdict.html#dontcare" rel="nofollow noreferrer">Prolog</a>). Here are some useful examples illustrating its unique behavior:</p> <pre><code>lambda { |x, x| 42 } # SyntaxError: duplicated argument name lambda { |_, _| 42 }.call(4, 2) # =&gt; 42 lambda { |_, _| 42 }.call(_, _) # NameError: undefined local variable or method `_' lambda { |_| _ + 1 }.call(42) # =&gt; 43 lambda { |_, _| _ }.call(4, 2) # 1.8.7: =&gt; 2 # 1.9.3: =&gt; 4 _ = 42 _ * 100 # =&gt; 4200 _, _ = 4, 2; _ # =&gt; 2 </code></pre> <p>These were all run in Ruby directly (with <code>puts</code>s added in)—not IRB—to avoid conflicting with its additional functionality.</p> <p>This is all a result of my own experimentation though, as I cannot find any documentation on this behavior anywhere (admittedly it's not the easiest thing to search for). Ultimately, I'm curious how all of this works internally so I can better understand exactly what is special about <code>_</code>. So I’m asking for references to documentation, and, preferably, the Ruby source code (and perhaps <a href="http://rubyspec.org/" rel="nofollow noreferrer">RubySpec</a>) that reveal how <code>_</code> behaves in Ruby.</p> <p><sub><em>Note: most of this arose out of <a href="https://stackoverflow.com/questions/9557485/hash-into-grouped-array/9557589#comment12116685_9557589">this discussion</a> with <a href="https://stackoverflow.com/users/916657/niklas-b">@Niklas B.</a></em></sub></p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USAndrew Marshall
    plurals
    1. PL
      singulars
      1. LTLinked
    1. PL
      singulars
      1. LTLinked
    2. PL
      singulars
      1. LTLinked
    3. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POWhere and how is the _ (underscore) variable specified?
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POWhere and how is the _ (underscore) variable specified?
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POWhere and how is the _ (underscore) variable specified?
      1. This table or related slice is empty.
      1. VTUpMod
    1. This table or related slice is empty.
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload