Avoid destroying record of last visual selection
author |
Daniel Robert Allen <allen.daniel.r@gmail.com> |
date |
Sun, 07 Apr 2013 11:33:46 -0700 |
parents |
f09f87e10570 |
children |
(none) |
Comparisons
===========
We've gone over conditionals, but `if` statements aren't very useful if we can't
compare things. Of course Vim lets us compare values, but it's not as
straightforward as it may seem.
Run the following commands:
:::vim
:if 10 > 1
: echom "foo"
:endif
Vim will, of course, display `foo`. Now run these commands:
:::vim
:if 10 > 2001
: echom "bar"
:endif
Vim displays nothing, because `10` is not greater than `2001`. So far
everything works as expected. Run these commands:
:::vim
:if 10 == 11
: echom "first"
:elseif 10 == 10
: echom "second"
:endif
Vim displays `second`. Nothing surprising here. Let's try comparing strings.
Run these commands:
:::vim
:if "foo" == "bar"
: echom "one"
:elseif "foo" == "foo"
: echom "two"
:endif
Vim echoes `two`. There's still nothing surprising, so what was I going on
about at the beginning of the chapter?
Case Sensitivity
----------------
Run the following commands:
:::vim
:set noignorecase
:if "foo" == "FOO"
: echom "vim is case insensitive"
:elseif "foo" == "foo"
: echom "vim is case sensitive"
:endif
Vim evaluates the `elseif`, so apparently Vimscript is case sensitive. Good to
know, but nothing earth-shattering. Now run these commands:
:::vim
:set ignorecase
:if "foo" == "FOO"
: echom "no, it couldn't be"
:elseif "foo" == "foo"
: echom "this must be the one"
:endif
**Whoa**. Stop right there. Yes, you saw that right.
**The behavior of `==` depends on a user's settings.**
I promise I'm not messing with you. Try it again and see. I'm not kidding,
I can't make this stuff up.
Code Defensively
----------------
What does this mean? It means that you can *never* trust the `==` comparison
when writing a plugin for other people to use. A bare `==` should *never*
appear in your plugins' code.
This idea is the same as the "`nmap` versus `nnoremap`" one. *Never* trust your
users' settings. Vim is old, vast, and complicated. When writing a plugin you
*have* to assume that users will have every variation of every setting.
So how can you get around this ridiculousness? It turns out that Vim has *two
extra sets* of comparison operators to deal with this.
Run the following commands:
:::vim
:set noignorecase
:if "foo" ==? "FOO"
: echom "first"
:elseif "foo" ==? "foo"
: echom "second"
:endif
Vim displays `first` because `==?` is the "case-insensitive no matter what the
user has set" comparison operator. Now run the following commands:
:::vim
:set ignorecase
:if "foo" ==# "FOO"
: echom "one"
:elseif "foo" ==# "foo"
: echom "two"
:endif
Vim displays `two` because `==#` is the "case-sensitive no matter what the user
has set" comparison operator.
The moral of this story is that you should *always* use explicit case sensitive
or insensitive comparisons. Using the normal forms is *wrong* and it *will*
break at some point. Save yourself the trouble and type the extra character.
When you're comparing integers this distinction obviously doesn't matter.
Still, I feel that it's better to use the case-sensitive comparisons everywhere
(even where they're not strictly needed), than to forget them in a place that
they *are* needed.
Using `==#` and `==?` with integers will work just fine, and if you change them
to strings in the future it will work correctly. If you'd rather use `==` for
integers that's fine, just remember that you'll need to change the comparison if
you change them to strings in the future.
Exercises
---------
Play around with `:set ignorecase` and `:set noignorecase` and see how various
comparisons act.
Read `:help ignorecase` to see why someone might set that option.
Read `:help expr4` to see all the available comparison operators.