firebase-ios-sdk/Firestore/Swift/Source/SwiftAPI/Pipeline/Selectable.swift

// Copyright 2025 Google LLC
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// Licensed under the Apache License, Version 2.0 (the "License");
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//      http://www.apache.org/licenses/LICENSE-2.0
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/// A protocol for expressions that have a name.
///
/// `Selectable` is adopted by expressions that can be used in pipeline stages where a named output
/// is required, such as `select` and `distinct`.
///
/// A `Field` is a `Selectable` where the name is the field path.
///
/// An expression can be made `Selectable` by giving it an alias using the `.as()` method.
public protocol Selectable: Sendable {}