For Dummies 978-0-470-56348-9 Datový list stáhnout pdf

Chapter 1: Programming

Dynamically!

In This Chapter

✓ Understanding dynamic typing

✓ Defining variables

✓ Putting dynamic to use

✓ Making static operations dynamic

or many years, I thought that dynamic programming referred to being

really flashy and flamboyant while writing code. So, I started wearing

Hawaiian shirts and singing loudly.

Later, I found out this isn’t the case.

Dynamic programming is another one of those buzzwords that really doesn’t

have a clear definition. At its loosest, it means developing something in such

a way that the program makes more decisions about the way it runs while

running, rather than when you compile it.

Scripting languages are a great example of this. When you write something

in VBScript, you don’t compile it at all — all of the decisions are made at

runtime. Ruby is another good example: Most of the time, an entire program

can just be typed into a command prompt and run right from there.

There are examples that are not so good — like VB Classic. Remember the

Variant type? You could declare a variable to be Variant and VB wouldn’t

decide what it was supposed to be for real until the program ran. In the

best of cases, this added immense flexibility to the language. In the worst of

cases, you got Type Mismatch errors at runtime.

To give a concrete example, when you declare a variable in a dynamically

typed language, you don’t have to say what type you are making that vari-

able. The compiler will just figure it out for you. In a static language, like C#

3.0, you do have to say what type you are making that variable.

Microsoft originally promised that dynamic types would never be in C#,

but later decided that the feature had to be added. Why? Mostly, it’s

because of the development for Microsoft Office (like the reasoning for

much of the rest of Book VIII). Office uses COM, the pre-.NET structure for

Microsoft applications.

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Chapter 1: Programming Dynamically!In This Chapter✓ Understanding dynamic typing✓ Defining variables✓ Putting dynamic to use✓ Making static operations

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778Running with the Dynamic Language Runtime def main Array.new(11) { gets.to_i }.reverse.each do |x| y = f(x) puts “#{x} #{(y>400) ?

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Book VIIIChapter 1Programming Dynamically!779Running with the Dynamic Language Runtime dynamic y = f(array[i]); if (y &g

Strany 4 - Programming Dynamically

780Running with the Dynamic Language RuntimeAdd to that the reality that C# is making runtime decisions about every single variable throughout the ent

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770Shifting C# Toward Dynamic TypingCOM expects that the languages that use it (like VB Classic and C++) will have dynamic types. This made developing

Strany 6 - Putting Dynamic to Use

Book VIIIChapter 1Programming Dynamically!771Shifting C# Toward Dynamic Typing ✦ Python ✦ Cobra (my new favorite) ✦ Groovy ✦ Boo ✦ NewspeakProgrammers

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772Programming DynamicallyOther benefits to dynamic languages in general show up as you use them more. For instance, macro languages are usually dynam

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Book VIIIChapter 1Programming Dynamically!773Programming DynamicallyHowever, we can do this:dynamic newCourse = SomeFunction();newCourse.Schedule();Al

Strany 9 - Dynamic Ruby

774Putting Dynamic to UseWhat happens if newCourse comes back as something that doesn’t have a Schedule method? You get a runtime error. But there are

Strany 10 - Dynamic C#

Book VIIIChapter 1Programming Dynamically!775Putting Dynamic to Use ✦ int newString = (int) dynamicVariable;: This is an explicit cast to int. The com

Strany 11 - Chapter 1

776Running with the Dynamic Language RuntimeHere is the compiled C# code: class C { [return: Dynamic] public object MyMethod([Dyna

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Book VIIIChapter 1Programming Dynamically!777Running with the Dynamic Language Runtime Figure 1-1: The Dynamic Language Runtime. The runtime helps the

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