An alias is a FIDL declaration that assigns a new name to an existing type. This has several benefits:

• Using alias ensures that there is a single source of truth for the concept the aliased type represents.
• It provides a way to name things, especially constrained types.
• Disparate uses of the now-aliased type may be linked as being instances of the same concept.

It is important to note that aliases do not carry through to the generated bindings code at the moment. In other words, the name assigned to an alias declaration will never appear as a declaration name in the generated FIDL code.

In this example, adding an alias for Key allows us to avoid repetition with a bespoke name, while also making clear to the reader that both the key value on the Item type and the key used in the ReadItem request struct are purposefully, and not merely coincidentally, the same thing.

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