chapters/06.markdown @ 41e61b3dce7a

Leaders
=======

We've learned how to map keys in a way that won't make us want to tear our hair
out later, but you might have noticed one more problem.

Every time we do something like `:nnoremap <space> dd` we've overwritten what
`<space>` normally does.  What if we need that key later?

There are a bunch of keys that you don't normally need in your day-to-day Vim
usage.  `-`, `H`, `L`, `<space>`, `<cr>`, and `<bs>` do things that you almost
never need (in normal mode, of course).  Depending on how you work you may find
others that you never use.

Those are safe to map, but that only gives us six keys to work with.  What
happened to Vim's legendary customizability?

Mapping Key Sequences
---------------------

Unlike Emacs, Vim makes it easy to map more than just single keys.  Run these
commands:

    :::vim
    :nnoremap -d dd
    :nnoremap -c ddO

Try them out by typing `-d` and `-c` (quickly) in normal mode.  The first
creates a custom mapping to delete a line, while the second "clears" a line and
puts you into insert mode.

This means you can pick a key that you don't care about (like `-`) as a "prefix"
key and create mappings on top of it.  It means you'll have to type an extra key
to activate the mappings, but one extra keystroke can easily be absorbed into
muscle memory.

If you think this might be a good idea, you're right, and it turns out that Vim
already has mechanisms for this "prefix" key!

Leader
------

Vim calls this "prefix" key "leader".  You can set your leader key to whatever
you like.  Run this command:

    :::vim
    :let mapleader = "-"

You can replace `-` with any key you like.  I personally like `,` even though it
shadows a useful function, because it's very easy to type.

When you're creating new mappings you can use `<leader>` to mean "whatever
I have my leader key set to".  Run this command:

    :::vim
    :nnoremap <leader>d dd

Now try it out by pressing your leader key and then `d`.  Vim will delete the
current line.

Why bother with setting `<leader>` at all, though?  Why not just include your
"prefix" key directly in your mapping commands?  There are three good reasons.

First of all, you may decide you need the normal function of your leader later
on down the road.  Defining it in one place makes it easy to change later.

Second, when someone else is looking at your `~/.vimrc` file they'll immediately
know what you mean when you say `<leader>`, and they can simply copy your
mapping into their own `~/.vimrc` if they like it even if they use a different
leader.

Finally, many Vim plugins create mappings that start with `<leader>`.  If you've
already got it set up they'll work properly and will feel familiar.

Local Leader
------------

Vim has a second "leader" key called "localleader".  This is meant to be
a prefix for mappings that only take effect for certain types of files, like
Python files or HTML files.

We'll talk about how to make mappings for specific types of files later in the
book, but you can go ahead and set your "localleader" now:

    :::vim
    :let maplocalleader = "\\"

Notice that we have to use `\\` and not just `\` because `\` is the escape
character in strings.  You'll learn more about this later.

Now you can use `<localleader>` in mappings and it will work just like
`<leader>` does, except for resolving to a different key.

Feel free to change this key to something else if you don't like backslash.

Exercises
---------

Read `:help mapleader`.

Read `:help maplocalleader`.

Set `mapleader` and `maplocalleader` in your `~/.vimrc` file.

Convert all the mappings you added to your `~/.vimrc` file in the previous
chapters to be prefixed with `<leader>` so they don't shadow existing commands.