The arglist is used to describe what the arguments to the constructor will be. In the simplest case something like :constructor make-foo a b c defines make-foo to be a three-argument constructor function whose arguments are used to initialize the slots named a, b, and c.
They work in the way you might expect, but there are a few fine points worthy of explanation. The first argument is used to initialize the a slot.
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The second argument is used to initialize the b slot. If there isn't any second argument, then the default value given in the body of the defstruct if given is used constructor option.
Named arguments enable you to specify an argument for a parameter by matching the argument with its name rather than with its position in the parameter list. Optional arguments enable you to omit arguments for some parameters.
The third argument is used to initialize the c slot. If there isn't any third argument, then the symbol sea is used instead. Any arguments following the third argument are collected into a list and used to initialize the d slot.
If there are three or fewer arguments, then nil is placed in the d slot. The e slot is not initialized; its initial value is undefined. Finally, the f slot is initialized to contain the symbol eff.
The Workbook class represents the entire spreadsheet as you see it in Excel and internally it represents the Excel file as it is written on disk. Constructor Create a new XlsxWriter Workbook object. Parameters: filename string — The name of the new Excel file to create. See below.
The actions taken in the b and e cases were carefully chosen to allow the user to specify all possible behaviors. With this definition, one can write create-foo 1 2 make-foo :a 1 :b 2 and of course create-foo provides defaulting different from that of make-foo.
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It is permissible to use the :constructor option more than once, so that you can define several different constructor functions, each taking different parameters. In addition, if there is a :p keyword argument, it is used to initialize the p slot; if there isn't any :p keyword argument, then the default value given in the body of the defstruct if given is used instead.
Similarly, if there is a :q keyword argument, it is used to initialize the q slot; if there isn't any :q keyword argument, then the symbol cue is used instead. In constructor option thoroughly to flog this presumably already dead horse, we further observe that if there is a :why keyword argument, it is used to initialize the y slot; otherwise the default value for slot y is used instead.
Similarly, if there is a :you keyword argument, it is used to initialize the u slot; otherwise the symbol ewe is used instead.
If memory serves me correctly, defstruct was included in the original design for Common Lisp some time before keyword arguments were approved.
The failure of positional constructors to accept keyword arguments may well have been an oversight on my part; there is no logical reason to exclude them.
I am grateful to X3J13 for rectifying this. I regret appearing to have more compassion for puns than for horses. As part of the same vote X3J13 also changed defstruct to allow BOA constructors to have parameters including supplied-p parameters that do not correspond to any slot.
Such parameters may be used in subsequent initialization forms in the parameter list. The standard constructor, make-ice-cream-factory, takes two keyword arguments named :capacity and :flavors. For this constructor, the default for the capacity slot is 3 and the default list of flavors is America's favorite threesome and a dark horse not a dead one.
Constructor HD Mission 1 Part 1
The BOA constructor fabricate-factory accepts four different keyword arguments. The :capacity argument defaults to 5, and the :flavors argument defaults in a complicated manner based on the other three. The :local-flavors argument may be specified directly, or may be constructor option to default based on the :location of the factory.
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- The Workbook Class — XlsxWriter Documentation
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- Named and Optional Arguments - C# Programming Guide | Microsoft Docs
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