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In computer programming, the pyramid of doom is a common problem that arises when a program uses many levels of nested indentation to control access to a function. It is commonly seen when checking for null pointers or handling callbacks. Two examples of the term are used to a particular programming style in JavaScript,〔(【引用サイトリンク】title=The Pyramid of Doom: A javaScript Style Trap )〕 and the nesting of if statements that occurs in object-oriented programming languages when one of the objects may be a null pointer.〔(【引用サイトリンク】title=New Language Features in Visual Basic 14 )〕 ==Examples== Most modern object oriented programming languages use a notation style known as "dot notation" that allows multiple method calls to be written in a single line of code, each call separated by a period. For instance: theWidth = windows("Main").views(5).size.width first looks in the array of windows for a window with the name "Main", gets the 5th subview within it, then calls the size method to return a structure with the view's dimensions, and finally calls the width method on that structure to produce a result that is assigned to theWidth.The problem with this approach is that the code assumes that all of these values are known to exist, for sure. While it is reasonable to suggest that a window will have a size and that size will have a width, it is not at all reasonable to assume that a window named "Main" will exist, nor that it has five subviews. If either of those possibilities are true, the size will be called on null, producing a null pointer error.To avoid this error, the programmer has to check every method call to ensure it returns a value. A safer version of the same code would be: if windows.contains("Main") If the programmer wishes to use that value based on whether or not it exists and is valid, the functional code inside the if statements is all pushed to the right, making it difficult to read longer lines. This often leads to attempts to "flatten" the code:if windows.contains("Main") if theWindow != null && theWindow.views.contains(5) if theView != null This sort of programming construct is very common and a number of programming languages have added some sort of syntactic sugar to address this. For instance, Apple's Swift added the concept of ''optional chaining'' in if statements〔(【引用サイトリンク】title=Optional Chaining )〕 while Microsoft's C# 6.0 and Visual Basic 14 added the ''null-conditional'' operators ?. and ?[ for member access and indexing, respectively.〔(【引用サイトリンク】title=Null-conditional Operators (C# and Visual Basic) )〕〔(【引用サイトリンク】title=What's New for Visual C# )〕〔(【引用サイトリンク】title=What's New for Visual Basic )〕 The basic idea is to allow a string of method calls to immediately return null if any of its members is null, so for instance:theWidth = windows("Main")?.views(5)?.size.width; would assign null to theWidth if either "Main" or the fifth subview is missing, or complete the statement and return the width if they are both valid. There are many times where the programmer wants to take different actions in these two cases, so Swift adds another form of syntactic sugar for this role, the if let statement:if let theView = windows("Main")?.views(5) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pyramid of doom (programming)」の詳細全文を読む スポンサード リンク
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