May 26, 2018

Roles with composition parameters

Roles are composable units of behavior. They are useful for factoring out functionality common to many classes from any part of your class hierarchy. See MooseCookbookRolesRecipe1 for an introduction to MooseRole.

While combining roles affords you a great deal of flexibility, individual roles have very little in the way of configurability. Core Moose provides alias for renaming methods and excludes for ignoring methods. These options are primarily perhaps solely for disambiguating role conflicts. See MooseCookbookRolesRecipe2 for more about alias and excludes.

Because roles serve many different masters, they usually provide only the least common denominator of functionality. To empower roles further, more configurability than alias and excludes is required. Perhaps your role needs to know which method to call when it is done. Or what default value to use for its url attribute.

Parameterized roles offer exactly this solution.

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