C++ 模板和 C# 泛型之间的区别(C# 编程指南)Differences Between C++ Templates and C# Generics (C# Programming Guide)

C# 泛型和 C++ 模板均是支持参数化类型的语言功能。C# Generics and C++ templates are both language features that provide support for parameterized types. 但是,两者之间存在很多不同。However, there are many differences between the two. 在语法层次,C# 泛型是参数化类型的一个更简单的方法,而不具有 C++ 模板的复杂性。At the syntax level, C# generics are a simpler approach to parameterized types without the complexity of C++ templates. 此外,C# 不试图提供 C++ 模板所具有的所有功能。In addition, C# does not attempt to provide all of the functionality that C++ templates provide. 在实现层次,主要区别在于 C# 泛型类型的替换在运行时执行,从而为实例化对象保留了泛型类型信息。At the implementation level, the primary difference is that C# generic type substitutions are performed at runtime and generic type information is thereby preserved for instantiated objects. 有关详细信息,请参阅运行时中的泛型For more information, see Generics in the Run Time.

以下是 C# 泛型和 C++ 模板之间的主要差异:The following are the key differences between C# Generics and C++ templates:

  • C# 泛型的灵活性与 C++ 模板不同。C# generics do not provide the same amount of flexibility as C++ templates. 例如,虽然可以调用 C# 泛型类中的用户定义的运算符,但是无法调用算术运算符。For example, it is not possible to call arithmetic operators in a C# generic class, although it is possible to call user defined operators.

  • C# 不允许使用非类型模板参数,如 template C<int i> {}C# does not allow non-type template parameters, such as template C<int i> {}.

  • C# 不支持显式定制化;即特定类型模板的自定义实现。C# does not support explicit specialization; that is, a custom implementation of a template for a specific type.

  • C# 不支持部分定制化:部分类型参数的自定义实现。C# does not support partial specialization: a custom implementation for a subset of the type arguments.

  • C# 不允许将类型参数用作泛型类型的基类。C# does not allow the type parameter to be used as the base class for the generic type.

  • C# 不允许类型参数具有默认类型。C# does not allow type parameters to have default types.

  • 在 C# 中,泛型类型参数本身不能是泛型,但是构造类型可以用作泛型。In C#, a generic type parameter cannot itself be a generic, although constructed types can be used as generics. C++ 允许使用模板参数。C++ does allow template parameters.

  • C++ 允许在模板中使用可能并非对所有类型参数有效的代码,随后针对用作类型参数的特定类型检查此代码。C++ allows code that might not be valid for all type parameters in the template, which is then checked for the specific type used as the type parameter. C# 要求类中编写的代码可处理满足约束的任何类型。C# requires code in a class to be written in such a way that it will work with any type that satisfies the constraints. 例如,在 C++ 中可以编写一个函数,此函数对类型参数的对象使用算术运算符 +-,在实例化具有不支持这些运算符的类型的模板时,此函数将产生错误。For example, in C++ it is possible to write a function that uses the arithmetic operators + and - on objects of the type parameter, which will produce an error at the time of instantiation of the template with a type that does not support these operators. C# 不允许此操作;唯一允许的语言构造是可以从约束中推断出来的构造。C# disallows this; the only language constructs allowed are those that can be deduced from the constraints.

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