比较泛型与模版

Key differences between generics and C++ templates:

• Generics are generic until the types are substituted for them at runtime. Templates are specialized at compile time so they are not still parameterized types at runtime

• The common language runtime specifically supports generics in MSIL. Because the runtime knows about generics, specific types can be substituted for generic types when referencing an assembly containing a generic type. Templates, in contrast, resolve into ordinary types at compile time and the resulting types may not be specialized in other assemblies.

• Generics specialized in two different assemblies with the same type arguments are the same type. Templates specialized in two different assemblies with the same type arguments are considered by the runtime to be different types.

• Generics are generated as a single piece of executable code which is used for all reference type arguments (this is not true for value types, which have a unique implementation per value type). The JIT compiler knows about generics and is able to optimize the code for the reference or value types that are used as type arguments. Templates generate separate runtime code for each specialization.

• Generics do not allow non-type template parameters, such as template <int i> C {}. Templates allow them.

• Generics do not allow explicit specialization (that is, a custom implementation of a template for a specific type). Templates do.

• Generics do not allow partial specialization (a custom implementation for a subset of the type arguments). Templates do.

• Generics do not allow the type parameter to be used as the base class for the generic type. Templates do.

• Generics do not allow type parameters to have default values. Templates do.

• Templates support template-template parameters (e.g. template<template<class T> class X> class MyClass), but generics do not.