Why are Anonymous Struct Declarations in Go Considered \"Short Notation\"?

Understanding Differences between Anonymous Struct Declarations

Anonymous structs are a convenient way to define structs without assigning a name to them. They are primarily used in situations where a specific struct definition is not crucial or when the struct is only intended to hold and pass data. The following code snippet demonstrates two methods of declaring anonymous structs in Go:

<code class="go">var Foo = map[string]struct{}{
  "foo": struct{}{},
}</code>

<code class="go">var Foo = map[string]struct{}{
  "foo": {},
}</code>

In the first declaration, an explicit type is specified as struct{}{}. This redundant type declaration is unnecessary as Gogland correctly identifies it as a warning. Go allows for the omission of the type in composite literals when the type is inferable from the context.

In the second declaration, the type is omitted, resulting in the form {}. This is sometimes referred to as "short notation" because it does not require specifying the type explicitly. When a composite literal is used within a map, the types of both key and value can be inferred from the map type itself.

Therefore, the declaration Foo = map[string]struct{}{"foo": {}} is equivalent to the first one, but with the type omission allowed by the Go language. This short notation does not alter the functionality of the anonymous struct; it is merely a syntactic difference.

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