chapters/26.markdown @ a0708167065a

Strings
=======

The next type of variable we'll look at is the String.  Since Vim is all about
manipulating text you'll be using this one quite a bit.

Run the following command:

    :::vim
    :echom "Hello"

Vim will echo "Hello".  So far, so good.

Concatenation
-------------

One of the most common things you'll want to do with strings is adding them
together.  Run this command:

    :::vim
    :echom "Hello, " + "world"

What happened?  Vim displayed "0" for some reason!

Here's the issue: Vim's `+` operator is *only* for Numbers.  When you pass
a string to `+` Vim will try to coerce it to a Number before performing the
addition.  Run the following command:

    :::vim
    :echom "3 mice" + "2 cats"

This time Vim displays "5", because the strings are coerced to the numbers "3"
and "2" respectively.

When I said "Number" I really *meant* Number.  Vim will *not* coerce strings to
Floats!  Try this command to see prove this:

    :::vim
    :echom 10 + "10.10"

Vim displays "20" because it dropped everything after the decimal point when
coercing "10.10" to a Number.

To combine strings you need to use the concatenation operator.  Run the
following command:

    :::vim
    :echom "Hello, " . "world"

This time Vim displays "Hello, world".  `.` is the "concatenate strings"
operator in Vim, which lets you combine strings.  It doesn't add whitespace or
anything else in between.

Coercion works both ways.  Kind of.  Try this command:

    :::vim
    :echom 10 . "foo"

Vim will display "10foo".  First it coerces `10` to a String, then it
concatenates it with the string on the right hand side.  Things get a bit
stickier when we're working with Floats, though.  Run this command:

    :::vim
    :echom 10.1 . "foo"

This time Vim throws an error, saying we're using a Float as a String.  Vim will
happily let you use a String as a Float when performing addition, but *won't*
let you use a Float as a String when concatenating.

The moral of this story is that Vim is a lot like Javascript: it allows you to
play fast and loose with types sometimes, but it's a really bad idea to do so
because it will come back to bite you at some point.

When writing Vimscript, make sure you know what the type of each of your
variables is.  If you need to change that type you should use a function to
explicitly change it, even if it's not strictly necessary at the moment.  Don't
rely on Vim's coercion because at some point you *will* regret it.

Special Characters
------------------

Like most programming languages, Vimscript lets you use escape sequences in
strings to represent hard-to-type characters.  Run the following command:

    :::vim
    :echom "foo \"bar\""

The `\"` in the string is replaced with a double quote character, as you would
probably expect.  Escape sequences work mostly as you would expect.  Run the
following command:

    :::vim
    :echom "foo\\bar"

Vim displays `foo\bar`, because `\\` is the escape sequence for a literal
backslash, just like in most programming languages.  Now run the following
command (note that it's an `echo` and *not* an `echom`):

    :::vim
    :echo "foo\nbar"

This time Vim will display two lines, "foo" and "bar", because the `\n` is
replaced with a newline.  Now try running this command:

    :::vim
    :echom "foo\nbar"

Vim will display something like "foo^@bar".  When you use `echom` with a String
instead of `echo` Vim will echo the exact characters of the string, which
sometimes means that it will show a different representation than plain old
`echo`.  `^@` is Vim's way of saying "newline character".

Literal Strings
---------------

Vim also lets you use "literal strings" to avoid excessive use of escape
sequences.  Run the following command:

    :::vim
    :echom '\n\\'

Vim displays `\n\\`.  Using single quotes tells Vim that you want the string
*exactly* as-in, with no escape sequences.  The one exception is that two single
quotes in a row will produce a single single quote.  Try this command:

    :::vim
    :echom 'That''s enough.'

Vim will display "That's enough."  Two single quotes is the *only* sequence that
has special meaning in a literal string.

We'll revisit literal strings when they become most useful, later in the book
(when we dive into regular expressions).

Truthiness
----------

You might be wondering how Vim treats strings when used in an `if` statement.
Run the following command:

    :::vim
    :if "foo"
    :  echo "yes"
    :else
    :  echo "no"
    :endif

Vim will display "no".  If you're wondering why this happens you should reread
the chapter on conditionals, because we talked about it there.

Exercises
---------

Read `:help expr-quote`.  Review the list of escape sequences you can use in
a normal Vim string.  Find out how to insert a tab character.

Try to figure out a way to insert a tab character into a string *without* using
an escape sequence.  Read `:help i_CTRL-V` for a hint.

Read `:help literal-string`.