This course is for experienced C programmers who want to program in C++. The examples and exercises require a basic understanding of algorithms and object-oriented software.
4.13 The Bigger Picture
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From the course by University of California, Santa Cruz
C++ For C Programmers, Part B
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From the lesson
Monte Carlo Hex Program, Further advanced C++ Topics and Patterns
This module shows how to use Monte Carlo evaluation in complex games such as Hex and Go. This had led top championship level play in both these games. The module discusses C++ assertions and exceptions for error handling and the new C++ 11 feature static asserts. Finally, the last part of the module introduces the idea of “Design Pattern”, a feature of modern OO programming.
Meet the Instructors
Ira PohlProfessor
Computer Science
Okay, so that's it for the language.
A language is a saying,
is a very big piece of work.
Let's you do lots of things.
But it doesn't let you do things necessarily in a good way.
How do you write a big piece of code so that you get an elegant result?
Well where do we see elegant results?
We see elegant results when we merge
an aesthetic component with a structural component.
Architects are not civil engineers and civil engineers aren't architects.
But yet the world has beautiful bridges.
The world has very unaesthetic bridges.
The world has simple building, storage sheds and
the world has a great buildings that have an artistic or aesthetic component.
When we write code, code should also be aesthetic.
Big code should have an aesthetic, we should be pleased with it.
We should be able to say, gee, that is elegant.
That makes a lot of sense, that's comprehensible.
So one of the things we try to teach you in the large,
is how to put it all together.
Architecture, here's a picture of the Stata building.
It's where computer science lives at MIT.
I had several dear friends there like the Turing Award winner Barbara Liskov.
Marvin Minsky, another Turing Award winner.
And here is this very unusual building, it may be a little bit controversial.
But very much less than the older industrial motif,
for some of you who've visited MIT.
MIT has In its older days a very much a little old brickyard industrial aesthetic.
And here you have this modern sort of brilliant architecture
in this very new computer science building.
Though again that's what we want, big pieces of code.
How do you put them together?
Well, in the 80s several of the better
programmers who are writing big pieces of
codes typically they were writing them
with these newer languages like Ada or
C++ or small talk,.
They started to ask what is it that gets us something
that we can structurally reuse and that does the job well?
And they ended up formulating this as what was
called a design pattern, design pattern.
This ideas called last as saying the last half of the 1980s.
The pioneers in the design pattern world decided that a design pattern should
have four essential owners and they were inspired by the way by a true architect.
So this came from them noticing that in the architectural literature,
there were people who also thought about well, and can have unique buildings.
But also there are patterns like show up that are very useful.
That they have to have a certain context and
we have to have a way of reference them.
So pattern has to have a name for example a name can be iterator.
We see an iterator as critical, critical in designing a big piece of software
namely the STL container classes, all need iterators.
So way to make use of them.
So way to organize pieces of code and do it effectively.
They have to solve a problem.
We're not interested in patterns that, or somehow
unique and maybe ones in a blue moon get used.
They have to solved a problem in which that problem recourse.
We need a solution so
it’s not just an after identify the same but we need that works well.
We need to see what the consequences of using that pattern.
Frequently a pattern is very general and not that official.
Sometimes it's really easy to use and you give up somethings for ease use.
So those are the four essential characteristics that were found
by the design pattern community.
So patterns occur in bigger classifications so
one class of patterns is creational.
By the way much of this was brought to the four by the gang of four.
There were four authors, Felacity, Johnson,
I'm forgetting a couple of the others who wrote
the design pattern book in the early 1990s that created a great stir.
All of a sudden people, have an aha moment.
They said, I've been using ideas like that but gee, I didn't know they were common
and I didn't know that I should try to systematize them.
And the gang of four in a beautiful book organized
a number of them, I don't know, 30 or 40 of them.
Organize them into different groupings, one for example, creational.
So in the creational patterns, one of those patterns is called the factory
method, and we're going to look at that in detail from the C++ perspective.
Patterns aren't necessarily
tied to any language they are a bigger architectural construct.
And so they can be used in the Python community or the C++ community or
the Java community as well as C# or C++.
A factory method is what is also know as virtual construction.
A way to accomplish it is to defer construction to subclasses.
Another kind of creational method is a singleton.
And the singleton needs code that assures that what ever is constructed
there's only a single instance of.
So here are two creational patterns.
We're going to see in detail how the factory method works.
And you could also imagine how you would write a singleton.
A singleton in C++ would mean that if I created an instance or
it creates an instance,
well if it was class based, it would probably be created by constructor.
Well, there would have to be some guarding primitive in there
I would say, I've already created the instance and
would disable any further instances from being created.
And that would be how you could manage a singleton pattern.
Singleton pattern is pretty easy, but it has some important
uses for example, somebody is grabbing a resource in the system in which
there is only one resource like writing to the screen.
And you can't have multiple versions of that.
So you'll have to disallow multiple versions.
Factory method again is something, virtual constructor is not allowed.
Remember, you can have virtual destructors in C++,
but you cannot have virtual constructor and yet the idea's a natural one.
Why shouldn't you have polymorphic construction as well as
polymorphic destruction?
And this pattern solves that common place problem.
There are also patterns that fit in to what
are called structural patterns.
Such a pattern includes a pattern
called the facade in which you provide a unified interface.
Another pattern that's very common,
especially in multithreaded current systems called the proxy.
In which you provide a surrogate, maybe to another machine.
So these are structural patterns and they get heavy use, and
they occur as big pieces of code in building some systems.
So again, this is all architectural.
Notice the character of the name, like facade or proxy.
They give you a vivid or factory method.
They give you a vivid way to think about something natural.
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