PGF 键 .initial 和 .default 之间的差异

Question 1

它们有两种不同的用途：使用定义的键/.initial=<value or string>是值存储键，其初始值设置为<value or string>。

如果没有提供参数，关键字/.default定义将使用什么值作为定义的键的参数。/.code=<code>

两者类似，但并不等同。一个键可以同时具有一个值（可以使用进行查询）\pgfkeysvalueof{/key}和一个代码（当您使用调用该键时将运行该代码）\pgfkeys{/key}。

如果没有.code定义，则可以使用.initial或，.default其行为几乎相同：使用\pgfkeys{/key/.initial=value}或设置值\pgfkeys{/key/.default=value}，使用查询值\pgfkeys{/key}。但是，如果您已定义.code，以及使用的值.initial，则要查询需要调用的值\pgfkeysvalueof{/key}。

\documentclass{article}
\usepackage{pgfkeys}

\begin{document}
%% Case 1: We want a key to store a value

% Just passing a value to an undefined key fails:
%\pgfkeys{firstkey=red}

% It first needs to be initialised
\pgfkeys{firstkey/.initial=red}

% Then we can get the value
\pgfkeys{firstkey}

% After the key has been initialised, we can change the stored value using simple assignments
\pgfkeys{firstkey=blue}
\pgfkeys{firstkey}

%% Case 2: We want a key to execute code using the argument
\pgfkeys{secondkey/.code=Your argument: \textbf{#1}}
\pgfkeys{secondkey=Some words}

% If we don't use an argument, it's assumed to be empty
\pgfkeys{secondkey}

% We can provide a default value to be used if no argument is provided:
\pgfkeys{secondkey/.default=Nothing}
\pgfkeys{secondkey}

% Let's define a .code key that just returns the argument...
\pgfkeys{/thirdkey/.code=#1}
% ...and give it an initial value...
\pgfkeys{/thirdkey/.initial=green}
% ...and a default argument
\pgfkeys{/thirdkey/.default=red}

% If we query the value, we get "green"
\pgfkeysvalueof{/thirdkey}
% If we run the code, we get "red"
\pgfkeys{/thirdkey}

\end{document}

Answer

它们有两种不同的用途：使用定义的键/.initial=<value or string>是值存储键，其初始值设置为<value or string>。

如果没有提供参数，关键字/.default定义将使用什么值作为定义的键的参数。/.code=<code>

两者类似，但并不等同。一个键可以同时具有一个值（可以使用进行查询）\pgfkeysvalueof{/key}和一个代码（当您使用调用该键时将运行该代码）\pgfkeys{/key}。

如果没有.code定义，则可以使用.initial或，.default其行为几乎相同：使用\pgfkeys{/key/.initial=value}或设置值\pgfkeys{/key/.default=value}，使用查询值\pgfkeys{/key}。但是，如果您已定义.code，以及使用的值.initial，则要查询需要调用的值\pgfkeysvalueof{/key}。

\documentclass{article}
\usepackage{pgfkeys}

\begin{document}
%% Case 1: We want a key to store a value

% Just passing a value to an undefined key fails:
%\pgfkeys{firstkey=red}

% It first needs to be initialised
\pgfkeys{firstkey/.initial=red}

% Then we can get the value
\pgfkeys{firstkey}

% After the key has been initialised, we can change the stored value using simple assignments
\pgfkeys{firstkey=blue}
\pgfkeys{firstkey}

%% Case 2: We want a key to execute code using the argument
\pgfkeys{secondkey/.code=Your argument: \textbf{#1}}
\pgfkeys{secondkey=Some words}

% If we don't use an argument, it's assumed to be empty
\pgfkeys{secondkey}

% We can provide a default value to be used if no argument is provided:
\pgfkeys{secondkey/.default=Nothing}
\pgfkeys{secondkey}

% Let's define a .code key that just returns the argument...
\pgfkeys{/thirdkey/.code=#1}
% ...and give it an initial value...
\pgfkeys{/thirdkey/.initial=green}
% ...and a default argument
\pgfkeys{/thirdkey/.default=red}

% If we query the value, we get "green"
\pgfkeysvalueof{/thirdkey}
% If we run the code, we get "red"
\pgfkeys{/thirdkey}

\end{document}

Question 2

虽然这并没有特别为已经提供的答案添加任何内容，但下面的例子帮助我更直观地理解了差异：

\documentclass{article}

\usepackage{pgfkeys}

\setlength{\parindent}{0mm}

\begin{document}

%% Create the keys, default values, etc.
\pgfkeys{%
  /mythingy/.is family, /mythingy,
  usecolor/.default = green,
  usecolor/.code = {You have chosen to use the color #1.},
  usecolor/.initial = purple,
}

%% Create a command that will use the keys
\newcommand{\mythingy}[1][]{%
  \pgfkeys{/mythingy, #1}   %% The usecolor/.code is executed
  \pgfkeysvalueof{/mythingy/usecolor}   %% Retrieves only the VALUE of the usecolor key
}

%% Use the command along with the keys in various different manners

\textbf{Attempt 1}:\\
%% Here, the usecolor/.code is executed using "blue" as the argument
\mythingy[usecolor=blue]

\vspace{\baselineskip}

\textbf{Attempt 2}:\\
%% Here, the usecolor/.code is execute using the /.default argument value "green"
\mythingy[usecolor]

\vspace{\baselineskip}

\textbf{Attempt 3}:\\
%% Here, the usecolor key is initialized to the /.initial value "purple"
%% However, the usecolor/.code is not executed !!!
\mythingy

\end{document}

输出为：

在此处输入图片描述

为了理解这种行为，理解以下概念的区别非常重要：键的值和与该键关联的代码的参数。

我可以想象这种区别以以下方式使用（参见下面的代码），尽管这个例子很怪诞（在我看来），因为它应该使用一个不同的第二个键radius来实际控制半径：

\documentclass{article}

\usepackage{tikz}
\usepackage{etoolbox}

\setlength{\parindent}{0mm}

\begin{document}

\pgfkeys{%
  /mypainter/.is family, /mypainter,
  drawcircle/.default = true,
  drawcircle/.code = {%
    \ifstrequal{#1}{true}{
      \begin{tikzpicture}
        \draw (0,0) circle[radius=\pgfkeysvalueof{/mypainter/drawcircle}];
      \end{tikzpicture}
    }{}
  },
  drawcircle/.initial = 1cm,
}

\newcommand{\mypainter}[1][]{%
  Executing {\ttfamily drawcircle/.code}: \pgfkeys{/mypainter, #1}
  \par
  Value of key {\ttfamily drawcircle}: \pgfkeysvalueof{/mypainter/drawcircle}
}

\textbf{Attempt 1}:\\
\mypainter[drawcircle=true]

\vspace{3\baselineskip}

\textbf{Attempt 2}:\\
\mypainter[drawcircle]

\vspace{3\baselineskip}

\textbf{Attempt 3}:\\
%% The order of the "keys" is important here (try switching the two)
\mypainter[drawcircle/.initial=2cm, drawcircle]

\vspace{3\baselineskip}

\textbf{Attempt 4}:\\
%% Notice the drawcircle/.initial now remains set to 2cm !!!
\mypainter

\vspace{3\baselineskip}

\textbf{Attempt 5}:\\
\mypainter[drawcircle=false]

\end{document}

最后一段代码的输出是：

drawcircle 示例的输出

Answer