javascript 是利用 function 來定義命名空間(scope)。在function 裡定義的變數是 local 變數，在function之外則存取不到。而 global 變數則是存在 function 之外，每一個 global 變數會變成一個global 物件的屬性(property)
1: myglobal = "hello"; // antipattern
2: console.log(myglobal); // "hello"
3: console.log(window.myglobal); // "hello"
4: console.log(window["myglobal"]); // "hello"
5: console.log(this.myglobal); // "hello"
使用 global 變數的問題
很容易跟其他人寫的 javascript 發生衝突，而此種衝突是最難發現的，有人在 global 定義了一個變數叫 result 則以下的 code 就會將 result 的值改變，造成潛在的 bug
1:function sum(x, y) {
2:// antipattern: implied global
3: result = x + y;
4:return result;
5: }
var 讓 result 這個變數變成 local ，就不會造成 global 的問題
1:function sum(x, y) {
2:// antipattern: implied global
3:var result = x + y;
4:return result;
5: }
小心這樣也會變成 global
chain assignments
1:function foo() {
2:// antipattern: do not use
3:var a = b = 0;
4:// ….
5: }
上面的 code 等同於 var a = (b = 0); 不小心就多了一個 global 變數，應該改為下面的寫法。
Abstract: See many of the major new language features in Delphi released after the Delphi 7 version
Language and Compiler Features Since Delphi 7
Inlining Routines can now be marked with the inline directive. This tells the compiler that, instead of actually calling the routine, it should emit code that includes the routine at the call site.
Operator Overloading
Delphi allows certain functions, or operators, to be overloaded within record declarations
TMyClass = class class operator Add(a, b: TMyClass): TMyClass; // Addition of two operands of type TMyClass class operator Subtract(a, b: TMyClass): TMyclass; // Subtraction of type TMyClass class operator Implicit(a: Integer): TMyClass; // Implicit conversion of an Integer to type TMyClass class operator Implicit(a: TMyClass): Integer; // Implicit conversion of TMyClass to Integer class operator Explicit(a: Double): TMyClass; // Explicit conversion of a Double to TMyClass end;
// Example implementation of Add class operator TMyClass.Add(a, b: TMyClass): TMyClass; begin ... end;
var x, y: TMyClassbegin x := 12; // Implicit conversion from an Integer y := x + x; // Calls TMyClass.Add(a, b: TMyClass): TMyClass b := b + 100; // Calls TMyClass.Add(b, TMyClass.Implicit(100)) end;
Class Helpers
A class helper is a type that - when associated with another class - introduces additional method names and properties which may be used in the context of the associated class (or its descendants). Class helpers are a way to extend a class without using inheritance. A class helper simply introduces a wider scope for the compiler to use when resolving identifiers. When you declare a class helper, you state the helper name, and the name of the class you are going to extend with the helper. You can use the class helper any place where you can legally use the extended class. The compiler's resolution scope then becomes the original class, plus the class helper. Class helpers provide a way to extend a class, but they should not be viewed as a design tool to be used when developing new code. They should be used solely for their intended purpose, which is language and platform RTL binding.
type TMyClass = class
procedure MyProc; function MyFunc: Integer; end;
...
procedure TMyClass.MyProc; var X: Integer; begin X := MyFunc; end;
function TMyClass.MyFunc: Integer; begin ... end;
...
type TMyClassHelper = class helper for TMyClass procedure HelloWorld; function MyFunc: Integer; end;
...
procedure TMyClassHelper.HelloWorld; begin WriteLn(Self.ClassName); // Self refers to TMyClass type, not TMyClassHelper
end;
function TMyClassHelper.MyFunc: Integer; begin ... end; ...
var X: TMyClass; begin X := TMyClass.Create; X.MyProc; // Calls TMyClass.MyProc X.HelloWorld; // Calls TMyClassHelper.HelloWorld X.MyFunc; // Calls TMyClassHelper.MyFunc
end;
strict private The private keyword actually creates a " friendship" relationship between classes in the same unit. The strict private declaration creates a true private field, not viewable by any other class, not even classes in the same unit.
strict protected Similar to the strict private declaration, strict protectedcreates a true protected member, visible only to the declaring class and its descendents.
Records with Methods
In addition to fields, records now may have properties and methods (including constructors), class properties, class methods, class fields, and nested types.
type TMyRecord = record type TInnerColorType = Integer; var Red: Integer; classvar Blue: Integer; procedure printRed(); constructor Create(val: Integer); property RedProperty: TInnerColorType read Red write Red; classproperty BlueProp: TInnerColorType read Blue write Blue; end;
constructor TMyRecord.Create(val: Integer); begin Red := val; end;
procedure TMyRecord.printRed; begin writeln('Red: ', Red); end;
class abstract
Classes, and not just methods, can be declared as abstract.
type TAbstractClass = classabstract procedure SomeProcedure; end;
class sealed Classes marked as sealed cannot be inherited from.
type TAbstractClass = class sealed procedure SomeProcedure; end;
class const Classes can now have class constants -- a constant value associated with the class itself and not an instance of the class.
type TClassWithConstant = class public const SomeConst = 'This is a class constant'; end;
procedure TForm1.FormCreate(Sender: TObject); begin ShowMessage(TClassWithConstant.SomeConst); end;
class type A class can now contain a type declaration that is usable only within that class.
type TClassWithClassType = class private type TRecordWithinAClass = record SomeField: string; end; public
classvar RecordWithinAClass: TRecordWithinAClass; end; ... procedure TForm1.FormCreate(Sender: TObject); begin TClassWithClassType.RecordWithinAClass.SomeField := 'This is a field of a class type declaration'; ShowMessage(TClassWithClassType.RecordWithinAClass.SomeField); end;
class var A class can also have a class variable, applicable only to the class and not an instance of the class. See "class type" for an example.
class property A class can have a class property, which is a property that applies only to the class reference and not to an instance of a class. The accessors for the class property must be either class methods or class variables. See the example in "static class methods" below.
nested classes Type declarations can be nested within class declarations. They present a way to keep conceptually related types together, and to avoid name collisions.
type TOuterClass = class strict private MyField: Integer; public type TInnerClass = class public MyInnerField: Integer; procedure InnerProc; end; procedure OuterProc; end;
procedure TOuterClass.TInnerClass.InnerProc; begin ... end;
final methods A virtual method that you override can now be marked final, preventing derived classes from overriding that method.
TAbstractClass = classabstract public procedure Bar; virtual; end;
TSealedClass = classsealed(TAbstractClass) public procedure Bar; override; end;
TFinalMethodClass = class(TAbstractClass) public procedure Bar; override; final; end;
sealed methods Classes marked as sealed cannot be descended from. See the example in 'final methods'.
static class methods Classes can have static class methods -- i.e. methods that can be called from a class type. Class static methods can be accessed without an object reference. Unlike ordinary class methods, class static methods have no Self parameter at all. They also cannot access any instance members. (They still have access to class fields, class properties, and class methods.) Also unlike class methods, class static methods cannot be declared virtual.
type TMyClass = class strict private classvar FX: Integer; strict protected
// Note: accessors for class properties must be declared class static.
for-in loop Delphi 2007 for Win32 supports for-element-in-collection style iteration over containers. The following container iteration patterns are recognized by the compiler:
for Element in ArrayExpr do Stmt; for Element in StringExpr do Stmt; for Element in SetExpr do Stmt; for Element in CollectionExpr do Stmt;
