parametrised negative filter name

CHANGELOG.md

@@ -7,7 +7,7 @@
 - Added support for resolving superclass properties for not-NSObject subclasses
 - The `{% for %}` tag can now iterate over tuples, structures and classes via
   their stored properties.
-- Added method to add boolean filters with their negative counterparts prefixed with `!`
+- Added method to add boolean filters with their negative counterparts
 
 ### Bug Fixes
 

Sources/Extension.swift

@@ -20,9 +20,9 @@ open class Extension {
   }
 
   /// Registers boolean filter with it's negative counterpart prefixed with `!`
-  public func registerBooleanFilter(_ name: String, filter: @escaping (Any?) throws -> Bool?) {
+  public func registerBooleanFilter(name: String, negativeFilterName: String, filter: @escaping (Any?) throws -> Bool?) {
     filters[name] = .simple(filter)
-    filters["!\(name)"] = .simple {
+    filters[negativeFilterName] = .simple {
       guard let result = try filter($0) else { return nil }
       return !result
     }

Tests/StencilTests/FilterSpec.swift

@@ -185,7 +185,7 @@ func testFilter() {
 
     $0.it("can register boolean filters") {
       let repeatExtension = Extension()
-      repeatExtension.registerBooleanFilter("isPositive") { (value: Any?) in
+      repeatExtension.registerBooleanFilter(name: "isPositive", negativeFilterName: "isNegative") { (value: Any?) in
         if let value = value as? Int {
           return value > 0
         }
@@ -196,7 +196,7 @@ func testFilter() {
         .render(Context(dictionary: ["value": 1], environment: Environment(extensions: [repeatExtension])))
       try expect(result) == "true"
 
-      let negativeResult = try Template(templateString: "{{ value|!isPositive }}")
+      let negativeResult = try Template(templateString: "{{ value|isNegative }}")
         .render(Context(dictionary: ["value": -1], environment: Environment(extensions: [repeatExtension])))
       try expect(negativeResult) == "true"
     }