C with class
Class is a type
- Compile-time access control
- static type checking
- function definition under class, make a class more like an interface specification.
- new/delete
C++ Language Design Rules
Aims
- C++ makes programming more enjoyable for serious programmers
- C++ is a general-purpose programming language that
- is a better C
- supports data abstraction
- supports object-oriented programming
General Rules
- C++’s evolution must be driven by real problems
- Don’t get involved in a sterile quest for perfection
- C++ must be useful now
- Every feature must have a reasonably obvious implementation
- Always provide a transition path
- C++ is a language, not a complete system
- Provide comprehensive support for each supported style
- Don’t try to force people
Design Support Rules
- Support sound design notions
- Provider facilities for program organization
- Say what you mean
- All features must be affordable
- It is more important to allow a useful feature than to prevent every misuse
- Support composition of software from separately developed parts
Language-Technical Rules
- No implicit violations of the static type system
- Provide as good support for user-defined types as for built-in types
- Locality is good
- Avoid order dependencies
- If in doubt, pick the variant of a feature that is easiest to teach
- Syntax matters(often in perverse ways)
- Preprocessor usage should be eliminated
Low-Level Programming Support Rules
- Use traditional(dumb) linkers
- No gratuitous incompatibilities with C
- Leave no room for a lower-level language below C++(except assembler)
- What you don’t use, you don’t pay for(zero-overhead rule)
- If in doubt, provide means for manual control
Standardization
对于一个被广泛使用的语言，一个统一标准是必须的，简单来说，标准定义了什么是general的，什么是implementation-dependent。
标准委员会的组成非常复杂，有各种职业者，各个公司代表。
委员会的很多工作，不为大多数人所知，而且非常无聊。感觉与程序员的修养相悖，那些花了很多时间探究和定义的写法问题，恰恰是程序员不关心的，我们更多地关注最佳实践，而不是令人目眩的奇怪语法。
Examples
- Name look up - Namespace - Redefinition
- Lifetime of temporaries - EOS
- Keyword argument
- Restricted pointer
- Character sets
Libraries
Design Tradeoffs
- Emphasize run-time efficiency?
- Minimize recompilation after a change?
- Maximize portability across platforms?
- Enable users to extend the basic library?
- Allow user without source code available?
- Blend in with existing notations and styles?
- Be usable from code not written in C++?
- Be usable by novices?
Major Extensions
Run-Time Type information
- dynamic_cast
- It has a static check: the two objects must have derivation relation.
- It doesn’t require the target type is exactly what the obj is. The target type can be a parent class.
- typeid()
- You should try to avoid typeid() in a switch statement. In most cases, virtual function is more scalable.