Filters with parameters

CHANGELOG.md

@@ -22,6 +22,9 @@ _None_
 * Removed the `join` filter, as it's now integrated in `Stencil` proper.  
   [David Jennes](https://github.com/djbe)
   [#10](https://github.com/SwiftGen/StencilSwiftKit/pull/10)
+* Refactored the `snakeToCamelCase` filter to now accept an (optional) boolean parameter to control the `noPrefix` behaviour.  
+  [David Jennes](https://github.com/djbe)
+  [#41](https://github.com/SwiftGen/StencilSwiftKit/pull/41)
 
 ### New Features
 

README.md

@@ -27,7 +27,7 @@
 * [String filters](Documentation/filters-strings.md):
   * `escapeReservedKeywords`: Escape keywods reserved in the Swift language, by wrapping them inside backticks so that the can be used as regular escape keywords in Swift code.
   * `lowerFirstWord`
-  * `snakeToCamelCase` / `snakeToCamelCaseNoPrefix`
+  * `snakeToCamelCase`: Transforms text from snake_case to camelCase. By default it keeps leading underscores, unless a single optional argument is set to "true", "no" or "0".
   * `camelToSnakeCase`: Transforms text from camelCase to snake_case. By default it converts to lower case, unless a single optional argument is set to "false", "no" or "0".
   * `swiftIdentifier`: Transforms an arbitrary string into a valid Swift identifier (using only valid characters for a Swift identifier as defined in the Swift language reference)
   * `titlecase`

Sources/Environment.swift

@@ -15,7 +15,6 @@ public extension Extension {
     registerFilter("swiftIdentifier", filter: Filters.Strings.stringToSwiftIdentifier)
     registerFilter("lowerFirstWord", filter: Filters.Strings.lowerFirstWord)
     registerFilter("snakeToCamelCase", filter: Filters.Strings.snakeToCamelCase)
-    registerFilter("snakeToCamelCaseNoPrefix", filter: Filters.Strings.snakeToCamelCaseNoPrefix)
     registerFilter("camelToSnakeCase", filter: Filters.Strings.camelToSnakeCase)
     registerFilter("titlecase", filter: Filters.Strings.titlecase)
     registerFilter("hexToInt", filter: Filters.Numbers.hexToInt)

Sources/Filters+Strings.swift

@@ -62,30 +62,37 @@ extension Filters {
       return titlecase(string)
     }
 
-    static func snakeToCamelCase(_ value: Any?) throws -> Any? {
-      guard let string = value as? String else { throw Filters.Error.invalidInputType }
-      guard let noPrefix = try snakeToCamelCaseNoPrefix(value) else {
-        return nil
-      }
-      var prefixUnderscores = ""
-      for scalar in string.unicodeScalars {
-        guard scalar == "_" else { break }
-        prefixUnderscores += "_"
-      }
-
-      return prefixUnderscores + ("\(noPrefix)")
-    }
-
-    static func snakeToCamelCaseNoPrefix(_ value: Any?) throws -> Any? {
+    /// Converts snake_case to camelCase. Takes an optional Bool argument for removing any resulting
+    /// leading '_' characters, which defaults to false
+    ///
+    /// - Parameters:
+    ///   - value: the value to be processed
+    ///   - arguments: the arguments to the function; expecting zero or one boolean argument
+    /// - Returns: the camel case string
+    /// - Throws: FilterError.invalidInputType if the value parameter isn't a string
+    static func snakeToCamelCase(_ value: Any?, arguments: [Any?]) throws -> Any? {
+      let stripLeading = try Filters.parseBool(from: arguments, index: 0, required: false) ?? false
       guard let string = value as? String else { throw Filters.Error.invalidInputType }
 
+      let unprefixed: String
       if try containsAnyLowercasedChar(string) {
         let comps = string.components(separatedBy: "_")
-        return comps.map { titlecase($0) }.joined(separator: "")
+        unprefixed = comps.map { titlecase($0) }.joined(separator: "")
       } else {
         let comps = try snakecase(string).components(separatedBy: "_")
-        return comps.map { $0.capitalized }.joined(separator: "")
+        unprefixed = comps.map { $0.capitalized }.joined(separator: "")
       }
+
+      // only if passed true, strip the prefix underscores
+      var prefixUnderscores = ""
+      if !stripLeading {
+        for scalar in string.unicodeScalars {
+          guard scalar == "_" else { break }
+          prefixUnderscores += "_"
+        }
+      }
+
+      return prefixUnderscores + unprefixed
     }
 
     /// Converts camelCase to snake_case. Takes an optional Bool argument for making the string lower case,

Tests/StencilSwiftKitTests/StringFiltersTests.swift

@@ -71,7 +71,12 @@ class StringFiltersTests: XCTestCase {
     }
   }
 
-  func testSnakeToCamelCase() throws {
+  func testSnakeToCamelCase_WithNoArgsDefaultsToFalse() throws {
+    let result = try Filters.Strings.snakeToCamelCase("__y_z!", arguments: []) as? String
+    XCTAssertEqual(result, "__YZ!")
+  }
+
+  func testSnakeToCamelCase_WithFalse() throws {
     let expectations = [
       "string": "String",
       "String": "String",
@@ -97,12 +102,12 @@ class StringFiltersTests: XCTestCase {
     ]
 
     for (input, expected) in expectations {
-      let result = try Filters.Strings.snakeToCamelCase(input) as? String
+      let result = try Filters.Strings.snakeToCamelCase(input, arguments: ["false"]) as? String
       XCTAssertEqual(result, expected)
     }
   }
 
-  func testSnakeToCamelCaseNoPrefix() throws {
+  func testSnakeToCamelCase_WithTrue() throws {
     let expectations = [
       "string": "String",
       "String": "String",
@@ -128,7 +133,7 @@ class StringFiltersTests: XCTestCase {
     ]
 
     for (input, expected) in expectations {
-      let result = try Filters.Strings.snakeToCamelCaseNoPrefix(input) as? String
+      let result = try Filters.Strings.snakeToCamelCase(input, arguments: ["true"]) as? String
       XCTAssertEqual(result, expected)
     }
   }