Elisp: What's “feature”?

By Xah Lee. Date: . Last updated: .

Emacs's Concept of Feature

For example, type Alt+x describe-variable Enter features Enter. You'll see something like this:

ibuffer etags ring cc-mode cc-fonts cc-menus cc-cmds cc-styles cc-align cc-engine cc-vars cc-defs xlsl-mode encoded-kb speck sgml-mode dired info newcomment desktop recentf tree-widget wid-edit advice help-fns …

require and provide

The purpose of features is for emacs to know if a package is already loaded.

The features variable and the functions {provide, require}, is the mechanism.

The require function checks the features variable to see if a symbol is already there, if not, then load the file.

The provide function adds a symbol to the features list.

back to Elisp: require, load, load-file, autoload, feature, Explained

Writing Major Mode

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  14. Elisp: Syntax Table Tutorial

  1. Elisp: How to Name Your Major Mode
  2. Elisp: What's “feature”?
  3. Elisp: require, load, load-file, autoload, feature, Explained

Syntax Table

  1. Elisp: Syntax Table Tutorial
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  4. Elisp: How to Determine If Cursor is Inside String or Comment
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  6. Elisp: Find Matching Bracket Character
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