Parameterized Variables (Macros)

It is possible to pass parameters to TWiki variables. This is called a macro in a programming language.

To define a parameterized variable, set a variable that contains other variables, such as:

   * Set EXAMPLE = Example variable using %DEFAULT%, %PARAM1% and %PARAM2%
   * Set DEMO = Demo using %DEFAULT{ default="(undefined)" }%,
                %PARAM1{ default="(undefined)" }% and %PARAM2{ default="(undefined)" }%

A special %DEFAULT% variable denotes the default (nameless) parameter of the calling variable. Variables optionally may list a default="..." parameter that gets used in case the calling variable does not specify that parameter.

To use a parameterized variable (or call a macro), add parameters within the curly brackets, such as:

   * %EXAMPLE{ "foo" PARAM1="bar" PARAM2="baz" }%
   * %DEMO{ "demo" PARAM2="parameter 2" }% -- note that PARAM1 is missing

which resolves to:

Example variable using foo, bar and baz
Demo using demo, (undefined) and parameter 2 -- note that PARAM1 is missing

Parameters in the variable definition are expanded using the following sequence:

Parameter from variable call. In above example, %PARAM1% gets expanded to bar.
Session variable and preferences settings

Example

Define variables:

   * Set DRINK = red wine
   * Set FAVORITE = My %DEFAULT{default="favorite"}% dish is %DISH{default="steak"}%,
                    my %DEFAULT{default="favorite"}% drink is %DRINK%.

The default can be defined with a default parameter (%DISH{default="steak"}%), or as a preferences setting (Set DRINK = ...).

Use Variables:

%FAVORITE{ DISH="Sushi" DRINK="Sake" }%

Returns:
My favorite dish is Sushi, my favorite drink is Sake.

%FAVORITE{}%

Returns:
My favorite dish is steak, my favorite drink is red wine.

%FAVORITE{ "preferred" }%

Returns:
My preferred dish is steak, my preferred drink is red wine.

Related: TWikiVariables, IncludeTopicsAndWebPages