blocks|key|1353941|text|这在ruby中是不可能的。不能将“empty”属性传递给方法。你能得到的最接近的方法是传递nil：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1353942|ldap_get(base_dn,+filter,+nil,+X)|code-block|syntax|javascript|1353943|但是，这会将作用域设置为nil，而不是LDAP::LDAP_SCOPE_SUBTREE。|1353944|你能做的就是在你的方法中设置默认值：|1353945|def+ldap_get(base_dn,+filter,+scope+=+nil,+attrs+=+nil)
++scope+%7C%7C=+LDAP::LDAP_SCOPE_SUBTREE
++...+do+something+...
end|1353946|现在，如果您像上面那样调用该方法，行为将与您预期的一样。|1353947|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|T|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|U|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

This isn't possible with ruby currently. You can't pass 'empty' attributes to methods. The closest you can get is to pass nil:

<pre><code>ldap_get(base_dn, filter, nil, X)
</code></pre>

However, this will set the scope to nil, not LDAP::LDAP_SCOPE_SUBTREE.

What you can do is set the default value within your method:

<pre><code>def ldap_get(base_dn, filter, scope = nil, attrs = nil)
 scope ||= LDAP::LDAP_SCOPE_SUBTREE
 ... do something ...
end
</code></pre>

Now if you call the method as above, the behaviour will be as you expect.

blocks|key|1569153|text|使用options散列几乎总是更好。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1569154|def+ldap_get(base_dn,+filter,+options+=+{})
++options[:scope]+%7C%7C=+LDAP::LDAP_SCOPE_SUBTREE
++...
end

ldap_get(base_dn,+filter,+:attrs+=>+X)|code-block|syntax|javascript|1569155|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You are almost always better off using an options hash.

<pre><code>def ldap_get(base_dn, filter, options = {})
 options[:scope] ||= LDAP::LDAP_SCOPE_SUBTREE
 ...
end

ldap_get(base_dn, filter, :attrs =&gt; X)
</code></pre>

blocks|key|1569301|text|随着时间的推移，从版本2开始，Ruby支持命名参数：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1569302|def+ldap_get+(+base_dn,+filter,+scope:+"some_scope",+attrs:+nil+)
++p+attrs
end

ldap_get("first_arg",+"second_arg",+attrs:+"attr1,+attr2")+#+=>+"attr1,+attr2"|code-block|syntax|javascript|1569303|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Time has moved on and since version 2 Ruby supports named parameters:

<pre><code>def ldap_get ( base_dn, filter, scope: "some_scope", attrs: nil )
 p attrs
end

ldap_get("first_arg", "second_arg", attrs: "attr1, attr2") # =&gt; "attr1, attr2"
</code></pre>

blocks|key|1353899|text|不可能按照您定义的ldap_get的方式来做。但是，如果您像这样定义ldap_get：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1353900|def+ldap_get+(+base_dn,+filter,+attrs=nil,+scope=LDAP::LDAP_SCOPE_SUBTREE+)|code-block|syntax|javascript|1353901|现在，您可以：|1353902|ldap_get(+base_dn,+filter,+X+)|1353903|但是现在你有一个问题，你不能用前两个arg和最后一个arg来调用它(这个问题和以前一样，但是现在最后一个arg不同了)。|1353904|这样做的理由很简单:+Ruby中的每个参数都不需要有缺省值，所以您不能按照指定的方式调用它。例如，在您的示例中，前两个参数没有默认值。|1353905|entityMap^0|9|8|Y|8|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|10|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|12|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|13|8|@]|D|@]|E|$]]|$1|S|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|T|$]]

It isn't possible to do it the way you've defined <code>ldap_get</code>. However, if you define <code>ldap_get</code> like this:

<pre><code>def ldap_get ( base_dn, filter, attrs=nil, scope=LDAP::LDAP_SCOPE_SUBTREE )
</code></pre>

Now you can:

<pre><code>ldap_get( base_dn, filter, X )
</code></pre>

But now you have problem that you can't call it with the first two args and the last arg (the same problem as before but now the last arg is different). 

The rationale for this is simple: Every argument in Ruby isn't required to have a default value, so you can't call it the way you've specified. In your case, for example, the first two arguments don't have default values.

blocks|key|1354088|text|最近，我找到了一个绕过这个问题的方法。我想在array类中创建一个带有可选参数的方法，用于保留或丢弃数组中的元素。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1354089|我模拟这种情况的方式是传递一个数组作为参数，然后检查该索引处的值是否为零。|1354090|class+Array
++def+ascii_to_text(params)
++++param_len+=+params.length
++++if+param_len+>+3+or+param_len+<+2+then+raise+"Invalid+number+of+arguments+#{param_len}+for+2+%7C%7C+3."+end
++++bottom++=+params[0]
++++top+++++=+params[1]
++++keep++++=+params[2]
++++if+keep.nil?+==+false
++++++if+keep+==+1
++++++++self.map{%7Cx%7C+if+x+>=+bottom+and+x+<=+top+then+x+=+x.chr+else+x+=+x.to_s+end}
++++++else
++++++++raise+"Invalid+option+#{keep}+at+argument+position+3+in+#{p+params},+must+be+1+or+nil"
++++++end
++++else
++++++self.map{%7Cx%7C+if+x+>=+bottom+and+x+<=+top+then+x+=+x.chr+end}.compact
++++end
++end
end|code-block|syntax|javascript|1354091|使用不同的参数尝试我们的类方法：|1354092|array+=+[1,+2,+97,+98,+99]
p+array.ascii_to_text([32,+126,+1])+#+Convert+all+ASCII+values+of+32-126+to+their+chr+value+otherwise+keep+it+the+same+(That's+what+the+optional+1+is+for)|1354093|输出：["1",+"2",+"a",+"b",+"c"]|offset|length|style|CODE|1354094|好的，很酷，一切按计划进行。现在让我们检查一下，如果不传入数组中的第三个参数option+(1)，会发生什么情况。|1354095|array+=+[1,+2,+97,+98,+99]
p+array.ascii_to_text([32,+126])+#+Convert+all+ASCII+values+of+32-126+to+their+chr+value+else+remove+it+(1+isn't+a+parameter+option)|1354096|输出：["a",+"b",+"c"]|1354097|正如您所看到的，数组中的第三个选项已被删除，从而在方法中启动了一个不同的部分，并删除了不在我们范围内的所有ASCII值(32-126)|1354098|或者，我们可以在参数中将值发布为nil。它看起来类似于下面的代码块：|1354099|def+ascii_to_text(top,+bottom,+keep+=+nil)
++if+keep.nil?
++++self.map{%7Cx%7C+if+x+>=+bottom+and+x+<=+top+then+x+=+x.chr+end}.compact
++else
++++self.map{%7Cx%7C+if+x+>=+bottom+and+x+<=+top+then+x+=+x.chr+else+x+=+x.to_s+end}
end|1354100|entityMap^0|0|0|0|0|0|3|P|0|0|0|3|F|0|0|0|0^^$0|@$1|2|3|4|5|6|7|16|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|17|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|18|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|19|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|1A|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|1B|8|@$O|1C|P|1D|Q|R]]|9|@]|A|$]]|$1|S|3|T|5|6|7|1E|8|@]|9|@]|A|$]]|$1|U|3|V|5|F|7|1F|8|@]|9|@]|A|$G|H]]|$1|W|3|X|5|6|7|1G|8|@$O|1H|P|1I|Q|R]]|9|@]|A|$]]|$1|Y|3|Z|5|6|7|1J|8|@]|9|@]|A|$]]|$1|10|3|11|5|6|7|1K|8|@]|9|@]|A|$]]|$1|12|3|13|5|F|7|1L|8|@]|9|@]|A|$G|H]]|$1|14|3|-4|5|6|7|1M|8|@]|9|@]|A|$]]]|15|$]]

Recently I found a way around this. I wanted to create a method in the array class with an optional parameter, to keep or discard elements in the array.

The way I simulated this was by passing an array as the parameter, and then checking if the value at that index was nil or not.

<pre><code>class Array
 def ascii_to_text(params)
 param_len = params.length
 if param_len &gt; 3 or param_len &lt; 2 then raise "Invalid number of arguments #{param_len} for 2 || 3." end
 bottom = params[0]
 top = params[1]
 keep = params[2]
 if keep.nil? == false
 if keep == 1
 self.map{|x| if x &gt;= bottom and x &lt;= top then x = x.chr else x = x.to_s end}
 else
 raise "Invalid option #{keep} at argument position 3 in #{p params}, must be 1 or nil"
 end
 else
 self.map{|x| if x &gt;= bottom and x &lt;= top then x = x.chr end}.compact
 end
 end
end
</code></pre>

Trying out our class method with different parameters:

<pre><code>array = [1, 2, 97, 98, 99]
p array.ascii_to_text([32, 126, 1]) # Convert all ASCII values of 32-126 to their chr value otherwise keep it the same (That's what the optional 1 is for)
</code></pre>

output: <code>["1", "2", "a", "b", "c"]</code>

Okay, cool that works as planned. Now let's check and see what happens if we don't pass in the the third parameter option (1) in the array.

<pre><code>array = [1, 2, 97, 98, 99]
p array.ascii_to_text([32, 126]) # Convert all ASCII values of 32-126 to their chr value else remove it (1 isn't a parameter option)
</code></pre>

output: <code>["a", "b", "c"]</code>

As you can see, the third option in the array has been removed, thus initiating a different section in the method and removing all ASCII values that are not in our range (32-126)

Alternatively, we could had issued the value as nil in the parameters. Which would look similar to the following code block:

<pre><code>def ascii_to_text(top, bottom, keep = nil)
 if keep.nil?
 self.map{|x| if x &gt;= bottom and x &lt;= top then x = x.chr end}.compact
 else
 self.map{|x| if x &gt;= bottom and x &lt;= top then x = x.chr else x = x.to_s end}
end
</code></pre>

blocks|key|1569204|text|有可能:)只需更改定义|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1569205|def+ldap_get+(+base_dn,+filter,+scope=LDAP::LDAP_SCOPE_SUBTREE,+attrs=nil+)|code-block|syntax|javascript|1569206|至|1569207|def+ldap_get+(+base_dn,+filter,+*param_array,+attrs=nil+)
scope+=+param_array.first+%7C%7C+LDAP::LDAP_SCOPE_SUBTREE|1569208|作用域现在将位于数组中的第一个位置。当您提供3个参数时，您将分配base_dn、filter和attrs，并且param_array将为[]当提供4个或更多参数时，param_array将为argument1、or_more、and_more|1569209|缺点是..。这是不清楚的解决方案，真的很难看。这是为了回答在ruby中可以省略函数调用中间的参数:)|1569210|你必须做的另一件事是重写scope的默认值。|1569211|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

It is possible :)
Just change definition

<pre><code>def ldap_get ( base_dn, filter, scope=LDAP::LDAP_SCOPE_SUBTREE, attrs=nil )
</code></pre>

to 

<pre><code>def ldap_get ( base_dn, filter, *param_array, attrs=nil )
scope = param_array.first || LDAP::LDAP_SCOPE_SUBTREE
</code></pre>

scope will be now in array on its first place.
When you provide 3 arguments, then you will have assigned base_dn, filter and attrs and param_array will be []
When 4 and more arguments then param_array will be [argument1, or_more, and_more]

Downside is... it is unclear solution, really ugly. This is to answer that it is possible to ommit argument in the middle of function call in ruby :)

Another thing you have to do is to rewrite default value of scope.

blocks|key|1354167|text|您可以使用部分应用程序来做到这一点，尽管使用命名变量肯定会使代码更具可读性。John+Resig在2008年写了一篇关于如何在JavaScript中做到这一点的博客文章：http://ejohn.org/blog/partial-functions-in-javascript/|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1354168|Function.prototype.partial+=+function(){
++var+fn+=+this,+args+=+Array.prototype.slice.call(arguments);
++return+function(){
++++var+arg+=+0;
++++for+(+var+i+=+0;+i+<+args.length+&&+arg+<+arguments.length;+i%2B%2B+)
++++++if+(+args[i]+===+undefined+)
++++++++args[i]+=+arguments[arg%2B%2B];
++++return+fn.apply(this,+args);
++};
};|code-block|syntax|javascript|1354169|在Ruby中应用同样的原则可能是可能的(除了原型继承)。|1354170|entityMap|0|LINK|mutability|MUTABLE|url|http://ejohn.org/blog/partial-functions-in-javascript/^0|2D|1I|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]]|C|$]]|$1|D|3|E|5|F|7|W|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|X|8|@]|9|@]|C|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]]]

You could do this with partial application, although using named variables definitely leads to more readable code. John Resig wrote a blog article in 2008 about how to do it in JavaScript: <a href="http://ejohn.org/blog/partial-functions-in-javascript/" rel="nofollow">http://ejohn.org/blog/partial-functions-in-javascript/</a>

<pre><code>Function.prototype.partial = function(){
 var fn = this, args = Array.prototype.slice.call(arguments);
 return function(){
 var arg = 0;
 for ( var i = 0; i &lt; args.length &amp;&amp; arg &lt; arguments.length; i++ )
 if ( args[i] === undefined )
 args[i] = arguments[arg++];
 return fn.apply(this, args);
 };
};
</code></pre>

It would probably be possible to apply the same principle in Ruby (except for the prototypal inheritance).

If I define a Ruby functions like this:

<pre><code>def ldap_get ( base_dn, filter, scope=LDAP::LDAP_SCOPE_SUBTREE, attrs=nil )
</code></pre>

How can I call it supplying only the first 2 and the last args? Why isn't something like

<pre><code>ldap_get( base_dn, filter, , X)
</code></pre>

possible or if it is possible, how can it be done?

Ruby optional parameters

如果我像这样定义Ruby函数：def ldap_get ( base_dn, filter, scope=LDAP::LDAP_SCOPE_SUBTREE, attrs=nil )我怎么能说它只提供前两个和最后一个参数呢？为什么不像这样的东西ldap_get( base_dn, filter, , X)可能，或者如果它是可能的，怎么做？

问Ruby可选参数
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