Introduce CacheClearer to force-clear static caches

BlueprintUI/Sources/Element/UIViewElement.swift

@@ -131,11 +131,15 @@ public struct UIViewElementContext {
 }
 
 /// An private type which caches `UIViewElement` views to be reused for sizing and measurement.
-private final class UIViewElementMeasurer {
+final class UIViewElementMeasurer {
 
     /// The standard shared cache.
     static let shared = UIViewElementMeasurer()
 
+    var cachedViewCount: Int {
+        views.count
+    }
+
     /// Provides the size for the provided element by using a cached measurement view.
     func measure(
         element: some UIViewElement,
@@ -173,6 +177,10 @@ private final class UIViewElementMeasurer {
         }
     }
 
+    func removeAllObjects() {
+        views = [:]
+    }
+
     private var views: [Key: UIView] = [:]
 
     private struct Key: Hashable {

BlueprintUI/Sources/Internal/CacheClearer.swift

@@ -0,0 +1,18 @@
+import Foundation
+
+@_spi(CacheManagement)
+public struct CacheClearer {
+
+    /// Clears all static caches that are in use.
+    ///
+    /// Blueprint leverages static caching to improve performance however there are situations in which
+    /// this can cause object lifetimes to be extended unexpectedly, especially in cases where cached
+    /// views reference other objects.
+    ///
+    /// - WARNING: Clearing these caches can have global performance implications. This method
+    /// should be invoked sparingley and only after other workarounds to manage object lifetimes have failed.
+    @_spi(CacheManagement)
+    public static func clearStaticCaches() {
+        UIViewElementMeasurer.shared.removeAllObjects()
+    }
+}

BlueprintUI/Tests/UIViewElementTests.swift

@@ -181,6 +181,27 @@ class UIViewElementTests: XCTestCase {
             blueprintView.layoutIfNeeded()
         }
     }
+
+    func test_removeAllObjects() {
+
+        struct TestElement: UIViewElement {
+            func makeUIView() -> UIView {
+                UIView()
+            }
+
+            func updateUIView(_ view: UIView, with context: BlueprintUI.UIViewElementContext) {}
+        }
+
+        let measurer = UIViewElementMeasurer()
+
+        _ = measurer.measure(element: TestElement(), constraint: .unconstrained, environment: .empty)
+
+        XCTAssertEqual(measurer.cachedViewCount, 1)
+
+        measurer.removeAllObjects()
+
+        XCTAssertEqual(measurer.cachedViewCount, 0)
+    }
 }
 
 fileprivate final class TestView: UIView {

CHANGELOG.md

@@ -11,6 +11,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Added `CacheCleaner` which exposes a method to force Blueprint's static caches to be cleared. 
+
 ### Removed
 
 ### Changed

CacheCleanerTests.swift

@@ -0,0 +1,29 @@
+import XCTest
+@testable @_spi(CacheManagement) import BlueprintUI
+
+class CacheClearerTests: XCTestCase {
+
+    func test_clearStaticCaches() {
+
+        struct TestElement: UIViewElement {
+            func makeUIView() -> UIView {
+                UIView()
+            }
+
+            func updateUIView(_ view: UIView, with context: BlueprintUI.UIViewElementContext) {}
+        }
+
+        let _ = UIViewElementMeasurer.shared.measure(
+            element: TestElement(),
+            constraint: .unconstrained,
+            environment: .empty
+        )
+
+        XCTAssertEqual(UIViewElementMeasurer.shared.cachedViewCount, 1)
+
+        CacheClearer.clearStaticCaches()
+
+        XCTAssertEqual(UIViewElementMeasurer.shared.cachedViewCount, 0)
+    }
+}
+