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<qhelp>

<overview>

<p>

The built-in <code>len</code> function returns the length of an array, slice or similar, which is

never less than zero. Hence, checking whether the result of a call to <code>len</code> is negative

is either redundant or indicates a logic mistake.

</p>

<p>

The same applies to the built-in function <code>cap</code>, and to unsigned integer values.

</p>

</overview>

<recommendation>

<p>

Examine the length check to see whether it is redundant and can be removed, or a mistake that

should be fixed.

</p>

</recommendation>

<example>

<p>

The example below shows a function that returns the first element of an array, triggering a panic

if the array is empty:

</p>

<sample src="NegativeLengthCheck.go" />

<p>

However, the emptiness check is ineffective: since <code>len(xs)</code> is never less than zero,

the condition will never hold and no panic will be triggered. Instead, the index expression

<code>xs[0]</code> will cause a panic.

</p>

<p>

The check should be rewritten like this:

</p>

<sample src="NegativeLengthCheckGood.go" />

</example>

<references>

<li>Package builtin: <a href="https://golang.org/pkg/builtin/#cap">func cap</a>.</li>

<li>Package builtin: <a href="https://golang.org/pkg/builtin/#len">func len</a>.</li>

</references>

</qhelp>