Filter properties prefixed with _$

Sources/CustomDump/Diff.swift

@@ -85,9 +85,10 @@ public func diff<T>(_ lhs: T, _ rhs: T, format: DiffFormat = .default) -> String
       elementIndent: Int,
       elementSeparator: String,
       collapseUnchanged: Bool,
+      filter isIncluded: (Mirror.Child) -> Bool = { _ in true },
       areEquivalent: (Mirror.Child, Mirror.Child) -> Bool = { $0.label == $1.label },
       areInIncreasingOrder: ((Mirror.Child, Mirror.Child) -> Bool)? = nil,
-      _ transform: (inout Mirror.Child, Int) -> Void = { _, _ in }
+      map transform: (inout Mirror.Child, Int) -> Void = { _, _ in }
     ) {
       var lhsChildren = Array(lhsMirror.children)
       var rhsChildren = Array(rhsMirror.children)
@@ -156,6 +157,9 @@ public func diff<T>(_ lhs: T, _ rhs: T, format: DiffFormat = .default) -> String
         return
       }
 
+      lhsChildren.removeAll(where: { !isIncluded($0) })
+      rhsChildren.removeAll(where: { !isIncluded($0) })
+
       let name = rhsName.map { "\($0): " } ?? ""
       print(
         name
@@ -355,7 +359,8 @@ public func diff<T>(_ lhs: T, _ rhs: T, format: DiffFormat = .default) -> String
           suffix: ")",
           elementIndent: 2,
           elementSeparator: ",",
-          collapseUnchanged: false
+          collapseUnchanged: false,
+          filter: { $0.label.map { !$0.hasPrefix("_$") } ?? true }
         )
       }
 
@@ -371,7 +376,7 @@ public func diff<T>(_ lhs: T, _ rhs: T, format: DiffFormat = .default) -> String
         areEquivalent: {
           isIdentityEqual($0.value, $1.value) || isMirrorEqual($0.value, $1.value)
         },
-        { $0.label = "[\($1)]" }
+        map: { $0.label = "[\($1)]" }
       )
 
     case (_, .dictionary?, _, .dictionary?):
@@ -443,7 +448,7 @@ public func diff<T>(_ lhs: T, _ rhs: T, format: DiffFormat = .default) -> String
         elementIndent: 2,
         elementSeparator: ",",
         collapseUnchanged: false,
-        { child, _ in
+        map: { child, _ in
           if child.label?.first == "." {
             child.label = nil
           }
@@ -499,7 +504,8 @@ public func diff<T>(_ lhs: T, _ rhs: T, format: DiffFormat = .default) -> String
         suffix: ")",
         elementIndent: 2,
         elementSeparator: ",",
-        collapseUnchanged: false
+        collapseUnchanged: false,
+        filter: { $0.label.map { !$0.hasPrefix("_$") } ?? true }
       )
 
     case (_, .tuple?, _, .tuple?):
@@ -511,7 +517,7 @@ public func diff<T>(_ lhs: T, _ rhs: T, format: DiffFormat = .default) -> String
         elementIndent: 2,
         elementSeparator: ",",
         collapseUnchanged: false,
-        { child, _ in
+        map: { child, _ in
           if child.label?.first == "." {
             child.label = nil
           }

Sources/CustomDump/Dump.swift

@@ -101,8 +101,9 @@ func _customDump<T, TargetStream>(
       of mirror: Mirror,
       prefix: String,
       suffix: String,
+      filter isIncluded: (Mirror.Child) -> Bool = { _ in true },
       by areInIncreasingOrder: ((Mirror.Child, Mirror.Child) -> Bool)? = nil,
-      _ transform: (inout Mirror.Child, Int) -> Void = { _, _ in }
+      map transform: (inout Mirror.Child, Int) -> Void = { _, _ in }
     ) {
       out.write(prefix)
       if !mirror.children.isEmpty {
@@ -133,6 +134,7 @@ func _customDump<T, TargetStream>(
         } else {
           out.write("\n")
           var children = Array(mirror.children)
+          children.removeAll(where: { !isIncluded($0) })
           if let areInIncreasingOrder = areInIncreasingOrder {
             children.sort(by: areInIncreasingOrder)
           }
@@ -195,12 +197,13 @@ func _customDump<T, TargetStream>(
         dumpChildren(
           of: Mirror(value, children: children),
           prefix: "\(typeName(mirror.subjectType))\(id)(",
-          suffix: ")"
+          suffix: ")",
+          filter: { $0.label.map { !$0.hasPrefix("_$") } ?? true }
         )
       }
 
     case (_, .collection?):
-      dumpChildren(of: mirror, prefix: "[", suffix: "]", { $0.label = "[\($1)]" })
+      dumpChildren(of: mirror, prefix: "[", suffix: "]", map: { $0.label = "[\($1)]" })
 
     case (_, .dictionary?):
       if mirror.children.isEmpty {
@@ -220,13 +223,14 @@ func _customDump<T, TargetStream>(
                 < _customDump(rhsKey.base, name: nil, indent: 0, isRoot: false, maxDepth: 1)
             }
             : nil,
-          { child, _ in
+          map: { child, _ in
             guard let pair = child.value as? (key: AnyHashable, value: Any) else { return }
             let key = _customDump(
               pair.key.base, name: nil, indent: 0, isRoot: false, maxDepth: maxDepth - 1
             )
             child = (key, pair.value)
-          })
+          }
+        )
       }
 
     case (_, .enum?):
@@ -241,7 +245,7 @@ func _customDump<T, TargetStream>(
           of: associatedValuesMirror,
           prefix: "\(child.label ?? "@unknown")(",
           suffix: ")",
-          { child, _ in
+          map: { child, _ in
             if child.label?.first == "." {
               child.label = nil
             }
@@ -271,18 +275,24 @@ func _customDump<T, TargetStream>(
       )
 
     case (_, .struct?):
-      dumpChildren(of: mirror, prefix: "\(typeName(mirror.subjectType))(", suffix: ")")
+      dumpChildren(
+        of: mirror,
+        prefix: "\(typeName(mirror.subjectType))(",
+        suffix: ")",
+        filter: { $0.label.map { !$0.hasPrefix("_$") } ?? true }
+      )
 
     case (_, .tuple?):
       dumpChildren(
         of: mirror,
         prefix: "(",
         suffix: ")",
-        { child, _ in
+        map: { child, _ in
           if child.label?.first == "." {
             child.label = nil
           }
-        })
+        }
+      )
 
     default:
       if let value = stringFromStringProtocol(value) {

Tests/CustomDumpTests/DiffTests.swift

@@ -1159,6 +1159,28 @@ final class DiffTests: XCTestCase {
       """
     )
   }
+
+  func testObservationRegistrarFiltered() {
+    struct ObservationRegistrar: Equatable {}
+    struct Value: Equatable {
+      var name: String
+      let _$observationRegistrar = ObservationRegistrar()
+    }
+    let blobSr = Value(name: "Blob Sr.")
+    let blobJr = Value(name: "Blob Jr.")
+    XCTAssertNoDifference(
+      diff(
+        blobSr,
+        blobJr
+      ),
+      """
+        DiffTests.Value(
+      -   name: "Blob Sr."
+      +   name: "Blob Jr."
+        )
+      """
+    )
+  }
 }
 
 private struct Stack<State: Equatable>: CustomDumpReflectable, Equatable {

Tests/CustomDumpTests/DumpTests.swift

@@ -1301,4 +1301,32 @@ final class DumpTests: XCTestCase {
       )
     }
   #endif
+
+  func testObservationRegistrarFiltered() {
+    struct ObservationRegistrar {}
+    class Object {
+      let name = "Blob Sr."
+      let _$observationRegistrar = ObservationRegistrar()
+    }
+    XCTAssertNoDifference(
+      String(customDumping: Object()),
+      """
+      DumpTests.Object(
+        name: "Blob Sr."
+      )
+      """
+    )
+    struct Value {
+      let name = "Blob Jr."
+      let _$observationRegistrar = ObservationRegistrar()
+    }
+    XCTAssertNoDifference(
+      String(customDumping: Value()),
+      """
+      DumpTests.Value(
+        name: "Blob Jr."
+      )
+      """
+    )
+  }
 }