When do you need parentheses when initializing Go structs?

Initializing Go Structs with Parentheses

When initializing structs in Go, using parentheses is not necessary but can be preferred in certain situations.

Typically, a struct is initialized using braces, as seen in:

<code class="go">item1 := Item{1, "Foo"}</code>

However, it's equally valid to initialize a struct with parentheses:

<code class="go">item2 := (Item{2, "Bar"})</code>

Both lines create instances of the Item struct and assign them to item1 and item2 respectively. The reflection on both structures will return the same name.

The parentheses primarily serve to disambiguate the syntax when using a struct initialization within an if statement. Without parentheses, the following code will result in a compilation error:

<code class="go">if i := Item{3, "a"}; i.Id == 3 {
}</code>

The compiler cannot determine whether the opening brace belongs to the composite literal or the if statement body. Adding parentheses resolves this ambiguity:

<code class="go">if i := (Item{3, "a"}); i.Id == 3 {
}</code>

In this case, the parentheses explicitly indicate that the composite literal is the value assigned to i. For further details, refer to the "Struct in for loop initializer" page.

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