📄 2.6.htm
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<DT><SPAN class=docPubcolor><TT><I>expr1</I></TT> <SPAN
class=docPubcolor><SPAN class=docMonofont>..</SPAN></SPAN>
<TT><I>expr2</I></TT></SPAN>
<DD>
<P class=docList>Includes both expressions
(<TT><I>expr1</I></TT> <TT><=</TT> <TT>x</TT>
<TT><=</TT> <TT><I>expr2</I></TT>) </P>
<DT><SPAN class=docPubcolor><TT><I>expr1</I></TT> <SPAN
class=docPubcolor><SPAN class=docMonofont>...</SPAN></SPAN>
<TT><I>expr2</I></TT></SPAN>
<DD>
<P class=docList>Doesn't include the last expression
(<TT><I>expr1</I></TT> <TT><=</TT> <TT>x</TT>
<TT><</TT> <TT><I>expr2</I></TT>) </P></DD></DL><A
name=ruby-CHP-2-SECT-6.1.3></A>
<H5 class=docSection3Title>2.6.1.3 Logical operators</H5><A
name=IXT-2-127000></A>
<P class=docText>If the value of the entire expression can be
determined with the value of the left operand alone, the right
operand isn't evaluated. </P><A name=IXT-2-127001></A>
<DL class=docList><A name=IXT-2-127001></A>
<DT><SPAN class=docPubcolor><SPAN class=docPubcolor><SPAN
class=docMonofont>&& and</SPAN></SPAN></SPAN>
<DD>
<P class=docList>Returns <TT>true</TT> if both operands are
<TT>true</TT>. If the left operand is <TT>false</TT>,
returns the value of the left operand, otherwise returns the
value of the right operand. </P>
<DT><SPAN class=docPubcolor><SPAN class=docPubcolor><SPAN
class=docMonofont>|| or</SPAN></SPAN></SPAN>
<DD>
<P class=docList>Returns <TT>true</TT> if either operand is
<TT>true</TT>. If the left operand is <TT>true</TT>, returns
the value of the left operand, otherwise returns the value
of the right operand. </P>
<P class=docList>The operators <TT>and</TT> and <TT>or</TT>
have extremely low precedence. </P></DD></DL><A
name=ruby-CHP-2-SECT-6.1.4></A>
<H5 class=docSection3Title>2.6.1.4 Ternary operator</H5><A
name=IXT-2-127002></A>
<P class=docText>Ternary <TT>?:</TT> is the conditional
operator. It's another form of the <TT>if</TT> statement.
</P><A name=IXT-2-127003></A>
<DL class=docList>
<DT><SPAN class=docPubcolor><TT><I>a</I></TT> <SPAN
class=docPubcolor><SPAN class=docMonofont>?</SPAN></SPAN>
<TT><I>b</I></TT> <SPAN class=docPubcolor><SPAN
class=docMonofont>:</SPAN></SPAN> <TT><I>c</I></TT></SPAN>
<DD>
<P class=docList><A name=IXT-2-127003></A>If
<TT><I>a</I></TT> is <TT>true</TT>, evaluates
<TT><I>b</I></TT>, otherwise evaluates <TT><I>c</I></TT>.
It's best to insert spaces before and after the operators to
avoid mistaking the first part for the method
<TT><I>a</I></TT><TT>?</TT> and the second part for the
symbol <TT>:</TT><TT><I>c</I></TT>. </P></DD></DL><A
name=ruby-CHP-2-SECT-6.1.5></A>
<H5 class=docSection3Title>2.6.1.5 defined? operator</H5><A
name=IXT-2-127004></A>
<P class=docText><TT>defined?</TT> is a special operator that
takes the form of a method call to determine whether or not
the passed expression is defined. It returns a description
string of the expression, or <TT>nil</TT> if the expression
isn't defined. </P><A name=IXT-2-127005></A><A
name=IXTR3-4></A>
<DL class=docList>
<DT><SPAN class=docPubcolor><SPAN class=docPubcolor><SPAN
class=docMonofont>defined?</SPAN></SPAN>
<TT><I>variable</I></TT></SPAN>
<DD>
<P class=docList>True if <TT><I>variable</I></TT> is
initialized</P><PRE>foo = 42
defined? foo # => "local-variable"
defined? $_ # => "global-variable"
defined? bar # => nil (undefined)</PRE>
<DT><SPAN class=docPubcolor><SPAN class=docPubcolor><SPAN
class=docMonofont>defined?</SPAN></SPAN>
<TT><I>method_call</I></TT></SPAN>
<DD>
<P class=docList><A name=IXT-2-127005></A>True if a method
is defined (also checks arguments) </P><PRE>defined? puts # => "method"
defined? puts(bar) # => nil (bar is not defined here)
defined? unpack # => nil (not defined here)</PRE>
<DT><SPAN class=docPubcolor><SPAN class=docPubcolor><SPAN
class=docMonofont>defined? super</SPAN></SPAN></SPAN>
<DD>
<P class=docList>True if a method exists that can be called
with <TT>super</TT> </P><PRE>defined? super # => "super" (if it can be called)
defined? super # => nil (if it cannot be)</PRE>
<DT><SPAN class=docPubcolor><SPAN class=docPubcolor><SPAN
class=docMonofont>defined? yield</SPAN></SPAN></SPAN>
<DD>
<P class=docList>True if a code block has been passed</P><A
name=IXTR3-4></A><PRE>defined? yield # => "yield" (if there is a block passed)
defined? yield # => nil (if there is no block)</PRE></DD></DL><A
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