使用TArray< T>的原因是什么而不是T的阵列？ [英] What are the reasons to use TArray<T> instead of Array of T?
问题描述
MyType 的数组替换为 TArray< MyType> 。所以问题是 TArray< T> 使用而不是MyType数组的优缺点是什么？主要优点是较少繁琐的类型身份规则。考虑：
a：整数数组;
b：整数数组;
这两个变量不兼容。写一个编译器错误：
a：= b;
另一方面，如果您使用通用语法：
a：TArray< Integer> ;;
b：TArray< Integer> ;;
那么这两个变量是兼容的。
当然可以写
type
TIntegerArray = Integer数组;
但是所有各方都需要同意类型。如果所有的代码都在你的控制之下，这是很好的，但是当使用各种来源的代码时，通用的动态数组的出现就会有很大的区别。
要想起来，你可以使用通用数组类型作为通用方法的返回类型。
没有通用数组，你被迫声明一种这种形式：
TArrayOfT = T
的数组 在你的泛型类，这是相当凌乱。而且，如果您在非泛型类中编写通用方法，那么您无法做出该声明。通用数组也解决了这个问题。
TMyClass = class
class function Foo< T> ;:TArray< T> ;静态的;
结束
这一切都遵循 类型兼容性
两个未实例化的泛型被视为赋值
兼容，只有当它们相同或者是
常用类型的别名时。 p>
如果基本类型相同（或者是
常用类型的别名），并且类型参数是相同的，则两个实例化泛型被视为赋值
兼容。
I'm migrating a legacy Delphi application to Delphi-XE2, and I'm wondering if there's a good reason to replace the arrays defined as Array of MyType to TArray<MyType>. So the question is what are the pros and cons of TArray<T> usage instead of Array of MyType?
The main advantage is less onerous type identity rules. Consider:
a: array of Integer;
b: array of Integer;
These two variables are not assignment compatible. It is a compiler error to write:
a := b;
On the other hand if you use the generic syntax:
a: TArray<Integer>;
b: TArray<Integer>;
then these two variables are assignment compatible.
Sure, you can write
type
TIntegerArray = array of Integer;
But all parties need to agree on the same type. It's fine if all code is in your control, but when using code from a variety of sources, the advent of generic dynamic arrays makes a huge difference.
The other advantage that springs to mind, in similar vein, is that you can readily use the generic array type as the return type of a generic method.
Without the generic array you are compelled to declare a type of this form:
TArrayOfT = array of T
in your generic class, which is rather messy. And if you are writing a generic method in a non-generic class, then you've no way to make that declaration. Again the generic array solves the problem.
TMyClass = class
class function Foo<T>: TArray<T>; static;
end;
This all follows on from type compatibility rules described in the documentation like this:
Type Compatibility
Two non-instantiated generics are considered assignment compatible only if they are identical or are aliases to a common type.
Two instantiated generics are considered assignment compatible if the base types are identical (or are aliases to a common type) and the type arguments are identical.
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