# constraint(equalTo:) Returns a constraint that defines one item’s attribute as equal to another. ``` func constraint(equalTo anchor: NSLayoutAnchor) -> NSLayoutConstraint ``` ## Parameters `anchor` A layout anchor from an [`NSView`](/documentation/AppKit/NSView) or [`NSLayoutGuide`](/documentation/AppKit/NSLayoutGuide) object. You must use a subclass of [`NSLayoutAnchor`](/documentation/AppKit/NSLayoutAnchor) that matches the current anchor. For example, if you call this method on an [`NSLayoutXAxisAnchor`](/documentation/AppKit/NSLayoutXAxisAnchor) object, this parameter must be another [`NSLayoutXAxisAnchor`](/documentation/AppKit/NSLayoutXAxisAnchor). ## Return Value An [`NSLayoutConstraint`](/documentation/AppKit/NSLayoutConstraint) object that defines an equal relationship between the attributes represented by the two layout anchors. ## Discussion This method defines the relationship `first attribute = second attribute`. Where `first attribute` is the layout attribute represented by the anchor receiving this method call, and `second attribute` is the layout attribute represented by the `anchor` parameter. The constraints produced by the following two examples are identical. ```swift // Creating a constraint using NSLayoutConstraint NSLayoutConstraint(item: subview, attribute: .Leading, relatedBy: .Equal, toItem: view, attribute: .LeadingMargin, multiplier: 1.0, constant: 0.0).isActive = true // Creating the same constraint using constraintEqualToAnchor: let margins = view.layoutMarginsGuide subview.leadingAnchor.constraintEqualToAnchor(margins.leadingAnchor).isActive = true ``` ## See Also [`NSLayoutConstraint`](/documentation/AppKit/NSLayoutConstraint) The relationship between two user interface objects that must be satisfied by the constraint-based layout system. [`NSLayoutAnchor`](/documentation/AppKit/NSLayoutAnchor) A factory class for creating layout constraint objects using a fluent API. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)