65 lines
4 KiB
YAML
65 lines
4 KiB
YAML
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--- # Tests from the (Poignant Guide)
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in: >
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h3. False
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!<i/blix-neg.gif(Shape of a cat.)!
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_The cat Trady Blix. Frozen in emptiness. Immaculate whiskers rigid. Placid
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eyes of lake. Tail of warm icicle. Sponsored by a Very Powerful Pause Button._
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The darkness surrounding Blix can be called *negative space*. Hang on to that phrase.
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Let it suggest that the emptiness has a negative connotation. In a similar way,
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@nil@ has a slightly sour note that it whistles.
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Generally speaking, everything in Ruby has a positive charge to it. This spark
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flows through strings, numbers, regexps, all of it. Only two keywords wear a
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shady cloak: @nil@ and @false@ draggin us down.
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You can test that charge with an @if@ keyword. It looks very much like the
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@do@ blocks we saw in the last chapter, in that both end with an @end@.
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<pre>
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if plastic_cup
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print "Plastic cup is on the up 'n' up!"
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end
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</pre>
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If @plastic_cup@ contains either @nil@ or @false@, you won't see anything print
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to the screen. They're not on the @if@ guest list. So @if@ isn't going to run
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any of the code it's protecting.
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But @nil@ and @false@ need not walk away in shame. They may be of questionable
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character, but @unless@ runs a smaller establishment that caters to the bedraggled.
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The @unless@ keyword has a policy of only allowing those with a negative charge in.
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Who are: @nil@ and @false@.
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<pre>
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unless plastic_cup
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print "Plastic cup is on the down low."
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end
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</pre>
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You can also use @if@ and @unless@ at the end of a single line of code, if that's
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all that is being protected.
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<pre>
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print "Yeah, plastic cup is up again!" if plastic_cup
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print "Hardly. It's down." unless plastic_cup
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</pre>
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Now that you've met @false@, I'm sure you can see what's on next.
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out: "<h3>False</h3>\n\n\t<p><img src=\"i/blix-neg.gif\" align=\"left\" title=\"Shape of a cat.\" alt=\"Shape of a cat.\" /></p>\n\n\t<p><em>The cat Trady Blix. Frozen in emptiness. Immaculate whiskers rigid. Placid eyes of lake. Tail of warm icicle. Sponsored by a Very Powerful Pause Button.</em></p>\n\n\t<p>The darkness surrounding Blix can be called <strong>negative space</strong>. Hang on to that phrase. Let it suggest that the emptiness has a negative connotation. In a similar way, <code>nil</code> has a slightly sour note that it whistles.</p>\n\n\t<p>Generally speaking, everything in Ruby has a positive charge to it. This spark flows through strings, numbers, regexps, all of it. Only two keywords wear a shady cloak: <code>nil</code> and <code>false</code> draggin us down.</p>\n\n\t<p>You can test that charge with an <code>if</code> keyword. It looks very much like the <code>do</code> blocks we saw in the last chapter, in that both end with an <code>end</code>.</p>\n\n<pre>\n if plastic_cup\n print \"Plastic cup is on the up 'n' up!\" \n end\n</pre>\n\n\t<p>If <code>plastic_cup</code> contains either <code>nil</code> or <code>false</code>, you won’t see anything print to the screen. They’re not on the <code>if</code> guest list. So <code>if</code> isn’t going to run any of the code it’s protecting.</p>\n\n\t<p>But <code>nil</code> and <code>false</code> need not walk away in shame. They may be of questionable character, but <code>unless</code> runs a smaller establishment that caters to the bedraggled. The <code>unless</code> keyword has a policy of only allowing those with a negative charge in. Who are: <code>nil</code> and <code>false</code>.</p>\n\n<pre>\n unless plastic_cup\n print \"Plastic cup is on the down low.\" \n end\n</pre>\n\n\t<p>You can also use <code>if</code> and <code>unless</code> at the end of a single line of code, if that’s all that is being protected.</p>\n\n<pre>\n print \"Yeah, plastic cup is up again!\" if plastic_cup\n print \"Hardly. It's down.\" unless plastic_cup\n</pre>\n\n\t<p>Now that you’ve met <code>false</code>, I’m sure you can see what’s on next.<br />\n</p>"
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