In Python one can use the 'pass' statement to do nothing:
if true:
pass
Is there a similar statement in coffeescript? I'm trying to do a switch statement and do nothing if certain conditions are met.
switch variable:
when 5 then pass
else do variable
i'm a happy user of
switch x
when 1
null
when 2
y = 3
else
y = 4
since null is already in the language and does semantically transport that meaning of 'nothing'.
; would be (a very tiny bit) more efficient than null?Unlike in Python, empty blocks are (usually) valid in CoffeeScript. So you can simply use:
switch variable:
when 5 then
else
variable
Note that without the then it won't compile, which I find a bit odd. This works pretty generally, though:
if x
else if y
something()
else
somethingElse()
is perfectly valid CoffeeScript.
Because every expression has a value in CoffeeScript, a pass keyword, if it existed, would be equivalent to the value undefined. So, you could define
pass = undefined
and then use pass just like in Python:
switch variable
when 5
pass
else
do variable
I always use a semicolon for this:
switch variable
when 5 then ;
else do variable
This is because in javascript, a semicolon is a valid statement which also happens to do nothing.
Update: I just thought of another interesting way of doing this. You could define pass as a global variable and set it to undefined:
window.pass = undefined
switch variable
when 5 then pass
else do variable
The only thing you have to watch out for is using pass as a local variable or redefining the global pass variable. That would break your code.
If you use Google's closure compiler, you could annotate this variable so that it is a constant:
`/** @const */ var pass;`
But then it would have to go at the beginning of each file. You could write your own preprocessor to do that automatically, though.
This makes sense to me in coffeescript:
switch variable
when "a" then doSomething()
when "b" then break
This compiles to the following js:
switch (variable) {
case "a":
doSomething();
break;
case "b":
break;
}
Note: You shouldn't use null like @flow suggests, because it inserts an unnecessary statement like this
null;
pass because it can't be used in an if/else like pass can.