## Scopelint Error: Using Variable on Range Scope - How to Safely Refer to Loop Variables in Function Literals?

Scopelint Error: Using Variable on Range Scope

In a test function TestGetUID, the code encounters an error reported by scopelint, which warns against using the variable x from the range scope within function literals.

Consider the following code lines:

<code class="go">for _, x := range tests {
    t.Run(x.description, func(t *testing.T) {
        client := fake.NewSimpleClientset(x.objs...)
        actual := getUID(client, x.namespace)
        assert.Equal(t, x.expected, actual)
    })
}</code>

The error pertains to these lines because x is the loop variable within the range loop iterating over the tests slice. Scopelint detects that x is being used in function literals passed to t.Run(), which could lead to potential issues if the function literals are invoked after t.Run() has returned.

Cause and Best Practices

The issue arises because the compiler cannot guarantee that the function literals created and passed to t.Run() won't be called after t.Run() exits. If the function literals were called after t.Run() returns, they would refer to the x variable, which might have been overwritten with the value from the subsequent iteration of the loop.

Go vet raises this warning to prevent such unintended behavior, which can result in bugs or even data races if the function literals are executed concurrently in different goroutines.

The recommended best practice in such cases is to either pass the value of the loop variable to the function literal as an argument or to create a copy of the loop variable and refer to the copy within the function literal. Since the function literal's signature cannot be changed, the recommended solution is to create a copy, for example:

<code class="go">x2 := x</code>

After declaring this copy, the x identifier within the function literal will refer to the local copy, not the loop variable. Although assigning the same name to the copy may seem confusing, it clearly indicates the intention of using a copy.

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