feat: Allow subclassing templates (#79)

Sources/Environment.swift

@@ -1,9 +1,11 @@
 public struct Environment {
+  public let templateClass: Template.Type
   public let extensions: [Extension]
 
   public var loader: Loader?
 
-  public init(loader: Loader? = nil, extensions: [Extension]? = nil) {
+  public init(loader: Loader? = nil, extensions: [Extension]? = nil, templateClass: Template.Type = Template.self) {
+    self.templateClass = templateClass
     self.loader = loader
     self.extensions = [DefaultExtension()] + (extensions ?? [])
   }
@@ -30,7 +32,7 @@ public struct Environment {
   }
 
   public func renderTemplate(string: String, context: [String: Any]? = nil) throws -> String {
-    let template = Template(templateString: string, environment: self)
+    let template = templateClass.init(templateString: string, environment: self)
     return try template.render(context)
   }
 }

Sources/Loader.swift

@@ -51,7 +51,8 @@ public class FileSystemLoader: Loader, CustomStringConvertible {
         continue
       }
 
-      return try Template(path: templatePath, environment: environment, name: name)
+      let content: String = try templatePath.read()
+      return try environment.templateClass.init(templateString: content, environment: environment, name: name)
     }
 
     throw TemplateDoesNotExist(templateNames: [name], loader: self)
@@ -63,7 +64,8 @@ public class FileSystemLoader: Loader, CustomStringConvertible {
         let templatePath = try path.safeJoin(path: Path(templateName))
 
         if templatePath.exists {
-          return try Template(path: templatePath, environment: environment, name: templateName)
+          let content: String = try templatePath.read()
+          return try environment.templateClass.init(templateString: content, environment: environment, name: templateName)
         }
       }
     }

Sources/Template.swift

@@ -6,7 +6,7 @@ let NSFileNoSuchFileError = 4
 #endif
 
 /// A class representing a template
-public class Template: ExpressibleByStringLiteral {
+open class Template: ExpressibleByStringLiteral {
   let environment: Environment
   let tokens: [Token]
 
@@ -14,7 +14,7 @@ public class Template: ExpressibleByStringLiteral {
   public let name: String?
 
   /// Create a template with a template string
-  public init(templateString: String, environment: Environment? = nil, name: String? = nil) {
+  public required init(templateString: String, environment: Environment? = nil, name: String? = nil) {
     self.environment = environment ?? Environment()
     self.name = name
 
@@ -71,7 +71,7 @@ public class Template: ExpressibleByStringLiteral {
   }
 
   /// Render the given template
-  public func render(_ dictionary: [String: Any]? = nil) throws -> String {
+  open func render(_ dictionary: [String: Any]? = nil) throws -> String {
     return try render(Context(dictionary: dictionary, environment: environment))
   }
 }