Added relationer operators

7f374791 · Orkhan Alikhanov · 8225dd36 · 7f374791
Commit 7f374791 authored May 23, 2019 by Orkhan Alikhanov
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Sources/iOS/Layout/Layout.swift
+146 -76

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--- a/Sources/iOS/Layout/Layout.swift
+++ b/Sources/iOS/Layout/Layout.swift
@@ -198,61 +198,67 @@ public extension Layout {
  /**
   Constraints top of the view to its parent's.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func top(_ offset: CGFloat = 0) -> Layout {
+  func top(_ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.top, constant: offset)
+    return constraint(.top, relationer: relationer, constant: offset)
  }
  /**
   Constraints left of the view to its parent's.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func left(_ offset: CGFloat = 0) -> Layout {
+  func left(_ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.left, constant: offset)
+    return constraint(.left, relationer: relationer, constant: offset)
  }
  /**
   Constraints right of the view to its parent.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func right(_ offset: CGFloat = 0) -> Layout {
+  func right(_ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.right, constant: -offset)
+    return constraint(.right, relationer: relationer, constant: -offset)
  }
  /**
   Constraints leading of the view to its parent's.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func leading(_ offset: CGFloat = 0) -> Layout {
+  func leading(_ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.leading, constant: offset)
+    return constraint(.leading, relationer: relationer, constant: offset)
  }
  /**
   Constraints trailing of the view to its parent.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func trailing(_ offset: CGFloat = 0) -> Layout {
+  func trailing(_ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.trailing, constant: -offset)
+    return constraint(.trailing, relationer: relationer, constant: -offset)
  }
  /**
   Constraints bottom of the view to its parent's.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func bottom(_ offset: CGFloat = 0) -> Layout {
+  func bottom(_ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.bottom, constant: -offset)
+    return constraint(.bottom, relationer: relationer, constant: -offset)
  }
  /**
@@ -390,41 +396,45 @@ public extension Layout {
  /**
   Constraints horizontal center of the view to its parent's.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func centerX(_ offset: CGFloat = 0) -> Layout {
+  func centerX(_ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.centerX, constant: offset)
+    return constraint(.centerX, relationer: relationer, constant: offset)
  }
  /**
   Constraints vertical center of the view to its parent's.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func centerY(_ offset: CGFloat = 0) -> Layout {
+  func centerY(_ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.centerY, constant: offset)
+    return constraint(.centerY, relationer: relationer, constant: offset)
  }
  /**
   Constraints width of the view to its parent's.
   - Parameter offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func width(offset: CGFloat = 0) -> Layout {
+  func width(offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.width, constant: offset)
+    return constraint(.width, relationer: relationer, constant: offset)
  }
  /**
   Constraints height of the view to its parent's.
   - Parameter offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func height(offset: CGFloat = 0) -> Layout {
+  func height(offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.height, constant: offset)
+    return constraint(.height, relationer: relationer, constant: offset)
  }
  /**
@@ -445,61 +455,67 @@ public extension Layout {
  /**
   Constraints top of the view to its parent's safeArea.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func topSafe(_ offset: CGFloat = 0) -> Layout {
+  func topSafe(_ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.top, constant: offset, useSafeArea: true)
+    return constraint(.top, relationer: relationer, constant: offset, useSafeArea: true)
  }
  /**
   Constraints left of the view to its parent's safeArea.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func leftSafe(_ offset: CGFloat = 0) -> Layout {
+  func leftSafe(_ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.left, constant: offset, useSafeArea: true)
+    return constraint(.left, relationer: relationer, constant: offset, useSafeArea: true)
  }
  /**
   Constraints right of the view to its parent.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func rightSafe(_ offset: CGFloat = 0) -> Layout {
+  func rightSafe(_ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.right, constant: -offset, useSafeArea: true)
+    return constraint(.right, relationer: relationer, constant: -offset, useSafeArea: true)
  }
  /**
   Constraints leading of the view to its parent's safeArea.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func leadingSafe(_ offset: CGFloat = 0) -> Layout {
+  func leadingSafe(_ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.leading, constant: offset, useSafeArea: true)
+    return constraint(.leading, relationer: relationer, constant: offset, useSafeArea: true)
  }
  /**
   Constraints trailing of the view to its parent.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func trailingSafe(_ offset: CGFloat = 0) -> Layout {
+  func trailingSafe(_ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.trailing, constant: -offset, useSafeArea: true)
+    return constraint(.trailing, relationer: relationer, constant: -offset, useSafeArea: true)
  }
  /**
   Constraints bottom of the view to its parent's safeArea.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func bottomSafe(_ offset: CGFloat = 0) -> Layout {
+  func bottomSafe(_ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.bottom, constant: -offset, useSafeArea: true)
+    return constraint(.bottom, relationer: relationer, constant: -offset, useSafeArea: true)
  }
  /**
@@ -637,41 +653,45 @@ public extension Layout {
  /**
   Constraints horizontal center of the view to its parent's safeArea.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func centerXSafe(_ offset: CGFloat = 0) -> Layout {
+  func centerXSafe(_ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.centerX, constant: offset, useSafeArea: true)
+    return constraint(.centerX, relationer: relationer, constant: offset, useSafeArea: true)
  }
  /**
   Constraints vertical center of the view to its parent's safeArea.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func centerYSafe(_ offset: CGFloat = 0) -> Layout {
+  func centerYSafe(_ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.centerY, constant: offset, useSafeArea: true)
+    return constraint(.centerY, relationer: relationer, constant: offset, useSafeArea: true)
  }
  /**
   Constraints width of the view to its parent's safeArea.
   - Parameter offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func widthSafe(offset: CGFloat = 0) -> Layout {
+  func widthSafe(offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.width, constant: offset, useSafeArea: true)
+    return constraint(.width, relationer: relationer, constant: offset, useSafeArea: true)
  }
  /**
   Constraints height of the view to its parent's safeArea.
   - Parameter offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func heightSafe(offset: CGFloat = 0) -> Layout {
+  func heightSafe(offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.height, constant: offset, useSafeArea: true)
+    return constraint(.height, relationer: relationer, constant: offset, useSafeArea: true)
  }
  /**
@@ -692,21 +712,23 @@ public extension Layout {
  /**
   Constraints width of the view to a constant value.
   - Parameter _ width: A CGFloat value.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func width(_ width: CGFloat) -> Layout {
+  func width(_ width: CGFloat, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.constantWidth, constants: width)
+    return constraint(.constantWidth, relationer: relationer, constants: width)
  }
  /**
   Constraints height of the view to a constant value.
   - Parameter _ height: A CGFloat value.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func height(_ height: CGFloat) -> Layout {
+  func height(_ height: CGFloat, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.constantHeight, constants: height)
+    return constraint(.constantHeight, relationer: relationer, constants: height)
  }
  /**
@@ -725,66 +747,72 @@ public extension Layout {
   Constraints top of the view to the given anchor.
   - Parameter _ anchor: A LayoutAnchorable.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func top(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0) -> Layout {
+  func top(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.top, to: anchor, constant: offset)
+    return constraint(.top, to: anchor, relationer: relationer, constant: offset)
  }
  /**
   Constraints left of the view to the given anchor.
   - Parameter _ anchor: A LayoutAnchorable.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func left(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0) -> Layout {
+  func left(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.left, to: anchor, constant: offset)
+    return constraint(.left, to: anchor, relationer: relationer, constant: offset)
  }
  /**
   Constraints right of the view to the given anchor.
   - Parameter _ anchor: A LayoutAnchorable.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func right(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0) -> Layout {
+  func right(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.right, to: anchor, constant: -offset)
+    return constraint(.right, to: anchor, relationer: relationer, constant: -offset)
  }
  /**
   Constraints leading of the view to the given anchor.
   - Parameter _ anchor: A LayoutAnchorable.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func leading(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0) -> Layout {
+  func leading(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.leading, to: anchor, constant: offset)
+    return constraint(.leading, to: anchor, relationer: relationer, constant: offset)
  }
  /**
   Constraints trailing of the view to the given anchor.
   - Parameter _ anchor: A LayoutAnchorable.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func trailing(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0) -> Layout {
+  func trailing(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.trailing, to: anchor, constant: -offset)
+    return constraint(.trailing, to: anchor, relationer: relationer, constant: -offset)
  }
  /**
   Constraints bottom of the view to the given anchor.
   - Parameter _ anchor: A LayoutAnchorable.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func bottom(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0) -> Layout {
+  func bottom(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.bottom, to: anchor, constant: -offset)
+    return constraint(.bottom, to: anchor, relationer: relationer, constant: -offset)
  }
  /**
@@ -935,44 +963,48 @@ public extension Layout {
   Constraints horizontal center of the view to the given anchor.
   - Parameter _ anchor: A LayoutAnchorable.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func centerX(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0) -> Layout {
+  func centerX(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.centerX, to: anchor, constant: offset)
+    return constraint(.centerX, to: anchor, relationer: relationer, constant: offset)
  }
  /**
   Constraints vertical center of the view to the given anchor.
   - Parameter _ anchor: A LayoutAnchorable.
   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func centerY(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0) -> Layout {
+  func centerY(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.centerY, to: anchor, constant: offset)
+    return constraint(.centerY, to: anchor, relationer: relationer, constant: offset)
  }
  /**
   Constraints width of the view to the given anchor.
   - Parameter _ anchor: A LayoutAnchorable.
-   - Parameter offset: A CGFloat offset.
+   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func width(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0) -> Layout {
+  func width(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.width, to: anchor, constant: offset)
+    return constraint(.width, to: anchor, relationer: relationer, constant: offset)
  }
  /**
   Constraints height of the view to the given anchor.
   - Parameter _ anchor: A LayoutAnchorable.
-   - Parameter offset: A CGFloat offset.
+   - Parameter _ offset: A CGFloat offset.
+   - Parameter _ relationer: A LayoutRelationer.
   - Returns: A Layout instance to allow chaining.
   */
  @discardableResult
-  func height(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0) -> Layout {
+  func height(_ anchor: LayoutAnchorable, _ offset: CGFloat = 0, _ relationer: LayoutRelationer = LayoutRelationerStruct.equal) -> Layout {
-    return constraint(.height, to: anchor, constant: offset)
+    return constraint(.height, to: anchor, relationer: relationer, constant: offset)
  }
  /**
@@ -1051,21 +1083,23 @@ private extension Layout {
   Constraints the view to its parent according to the provided attribute.
   If the constraint already exists, will update its constant.
   - Parameter _ attribute: A LayoutAttribute.
+   - Parameter _ relationer: A LayoutRelationer.
   - Parameter constant: A CGFloat.
   - Returns: A Layout instance to allow chaining.
   */
-  func constraint(_ attribute: LayoutAttribute, constant: CGFloat, useSafeArea: Bool = false) -> Layout {
+  func constraint(_ attribute: LayoutAttribute, relationer: LayoutRelationer = LayoutRelationerStruct.equal, constant: CGFloat, useSafeArea: Bool = false) -> Layout {
-    return constraint([attribute], constants: constant, useSafeArea: useSafeArea)
+    return constraint([attribute], relationer: relationer, constants: constant, useSafeArea: useSafeArea)
  }
  /**
   Constraints the view to its parent according to the provided attributes.
   If any of the constraints already exists, will update its constant.
   - Parameter _ attributes: An array of LayoutAttribute.
+   - Parameter _ relationer: A LayoutRelationer.
   - Parameter constants: A list of CGFloat.
   - Returns: A Layout instance to allow chaining.
   */
-  func constraint(_ attributes: [LayoutAttribute], constants: CGFloat..., useSafeArea: Bool = false) -> Layout {
+  func constraint(_ attributes: [LayoutAttribute], relationer: LayoutRelationer = LayoutRelationerStruct.equal, constants: CGFloat..., useSafeArea: Bool = false) -> Layout {
    var attributes = attributes
    var anchor: LayoutAnchor!
@@ -1080,7 +1114,7 @@ private extension Layout {
      anchor = LayoutAnchor(constraintable: useSafeArea ? parent?.safeAnchor.constraintable : parent, attributes: attributes)
    }
-    return constraint(attributes, to: anchor, constants: constants)
+    return constraint(attributes, to: anchor, relationer: relationer, constants: constants)
  }
  /**
@@ -1088,11 +1122,12 @@ private extension Layout {
   If the constraint already exists, will update its constant.
   - Parameter _ attribute: A LayoutAttribute.
   - Parameter to anchor: A LayoutAnchorable.
+   - Parameter relation: A LayoutRelation between anchors.
   - Parameter constant: A CGFloat.
   - Returns: A Layout instance to allow chaining.
   */
-  func constraint(_ attribute: LayoutAttribute, to anchor: LayoutAnchorable, constant: CGFloat) -> Layout {
+  func constraint(_ attribute: LayoutAttribute, to anchor: LayoutAnchorable, relationer: LayoutRelationer = LayoutRelationerStruct.equal, constant: CGFloat) -> Layout {
-    return constraint([attribute], to: anchor, constants: constant)
+    return constraint([attribute], to: anchor, relationer: relationer, constants: constant)
  }
  /**
@@ -1100,11 +1135,12 @@ private extension Layout {
   If any of the constraints already exists, will update its constant.
   - Parameter _ attributes: An array of LayoutAttribute.
   - Parameter to anchor: A LayoutAnchorable.
+   - Parameter relation: A LayoutRelation between anchors.
   - Parameter constants: A list of CGFloat.
   - Returns: A Layout instance to allow chaining.
   */
-  func constraint(_ attributes: [LayoutAttribute], to anchor: LayoutAnchorable, constants: CGFloat...) -> Layout {
+  func constraint(_ attributes: [LayoutAttribute], to anchor: LayoutAnchorable, relationer: LayoutRelationer = LayoutRelationerStruct.equal, constants: CGFloat...) -> Layout {
-    return constraint(attributes, to: anchor, constants: constants)
+    return constraint(attributes, to: anchor, relationer: relationer, constants: constants)
  }
  /**
@@ -1112,17 +1148,18 @@ private extension Layout {
   If any of the constraints already exists, will update its constant.
   - Parameter _ attributes: An array of LayoutAttribute.
   - Parameter to anchor: A LayoutAnchorable.
+   - Parameter relation: A LayoutRelation between anchors.
   - Parameter constants: An array of CGFloat.
   - Returns: A Layout instance to allow chaining.
   */
-  func constraint(_ attributes: [LayoutAttribute], to anchor: LayoutAnchorable, constants: [CGFloat]) -> Layout {
+  func constraint(_ attributes: [LayoutAttribute], to anchor: LayoutAnchorable, relationer: LayoutRelationer, constants: [CGFloat]) -> Layout {
    let from = LayoutAnchor(constraintable: constraintable, attributes: attributes)
    var to = anchor as? LayoutAnchor
    if to?.attributes.isEmpty ?? true {
      let v = (anchor as? UIView) ?? (anchor as? LayoutAnchor)?.constraintable
      to = LayoutAnchor(constraintable: v, attributes: attributes)
    }
-    let constraint = LayoutConstraint(fromAnchor: from, toAnchor: to!, relation: .equal, constants: constants)
+    let constraint = LayoutConstraint(fromAnchor: from, toAnchor: to!, relation: relationer(.nil, .nil), constants: constants)
    let constraints = (view?.constraints ?? []) + (view?.superview?.constraints ?? [])
@@ -1140,3 +1177,36 @@ private extension Layout {
    return self
  }
 }
+/// A closure typealias for relation operators.
+public typealias LayoutRelationer = (LayoutRelationerStruct, LayoutRelationerStruct) -> LayoutRelation
+/// A dummy struct used in creating relation operators (==, >=, <=).
+public struct LayoutRelationerStruct {
+  /// Passed as an unused argument to the LayoutRelationer closures.
+  static let `nil` = LayoutRelationerStruct()
+  /**
+   A method used as a default parameter for LayoutRelationer closures.
+   Swift does not allow using == operator directly, so we had to create this.
+   */
+  public static func equal(left: LayoutRelationerStruct, right: LayoutRelationerStruct) -> LayoutRelation {
+    return .equal
+  }
+}
+/// A method returning `LayoutRelation.equal`
+public func ==(left: LayoutRelationerStruct, right: LayoutRelationerStruct) -> LayoutRelation {
+  return .equal
+}
+/// A method returning `LayoutRelation.greaterThanOrEqual`
+public func >=(left: LayoutRelationerStruct, right: LayoutRelationerStruct) -> LayoutRelation {
+  return .greaterThanOrEqual
+}
+/// A method returning `LayoutRelation.lessThanOrEqual`
+public func <=(left: LayoutRelationerStruct, right: LayoutRelationerStruct) -> LayoutRelation {
+  return .lessThanOrEqual
+}