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CoffeeScript Undefined
(8 answers)
Closed 8 years ago.
I often want to check if a variable or property is not null and not undefined in CS. Is there a shortcut for "truthy"-checks besides the postfix ? for undefined?
#Austin Mullins, Thats true but I assumed it produced that check for everything and found that the CoffeeScript compiler will produce different results based on the use of the variables.
Variables that are declared before use (assigned a value) check for != null. Even explicit assignment of undefined (the Javascript compiles to void 0 which returns undefined) won't change the compilers behaviour.
The result is the same regardless ? appears work as expected.
A demo of what I found (preview link), http://preview.tinyurl.com/cmo6xw7
Follow the link and click the Run button (top right)
The code...
((arg) ->
str = "Hello World!"
num = 42
foo = arg
# Lets see what the compiler produces
alert "str is #{str}" if str?
alert "num is #{num}" if num?
alert "foo is #{foo}" if foo?
# bar has not been assigned a value or used until now
alert "bar is #{bar}" if bar?
# Lets assign str to something that isn't straight up null
# cs will translate undefined into the expression that returns undefined
str = undefined
# Shorthand
if str?
alert "str? is #{str}"
else
alert "str? is empty"
# Explicit checks
if typeof str isnt "undefined" && str isnt null
alert "str explicit check is #{str}"
else
alert "str explicit check is empty"
).call()
Related
I want to get expression value from drools.The drl like this.
global java.util.Map $globalVar;
global java.lang.Object $result;
import java.util.Map;
function myFunc(Map map){
return "hello";
}
rule "onlyone"
when
$factMap: Map($tmpResult:(myFunc($globalVar)), eval(true))
then
$result = $tmpResult;
end
When the rule get exception,like this
Caused by: org.mvel2.PropertyAccessException: [unable to resolve method: java.util.Map.$globalVar() [argslength=0]]
The global variable $globarVar has no relation with the fact.
It is likely drools can't recognize the global variable.Is there any grammar error in my drl?
Your syntax is so wrong I can't even figure out what you're trying to do.
Functions are very simple, they're just like methods in Java. They even look like methods in Java -- yours is missing a return type.
function String myFunc(Map map) {
return "hello";
}
function String greeting(String name) {
return "Hello, " + name + ". How are you?"
}
You can invoke them in your rules as you would any other function, either on the left hand side ("when") or on the right hand side ("then").
rule "Apply Greeting and Send Memo"
when
$memo: Memo( $recipient: recipient, sent == false )
$greeting: String() from greeting($recipient)
then
MemoSender.send($greeting, $memo);
modify( $memo ) {
setSent(true)
};
end
rule "Apply Greeting and Send Memo - v2"
when
$memo: Memo( $recipient: recipient, sent == false )
then
String $greeting = greeting($recipient);
MemoSender.send( $greeting, $memo );
modify( $memo ) {
setSent(true)
}
end
The bits with the globals in your question are red herrings. Yes, they're not working and throwing errors, but the syntax is so wrong that I'm not sure how it was supposed to work in the first place.
One way you might interact with a global in a function would possibly be something like ...
global Float taxRate; // passed in as a global because it's an external constant value
global Float freeShippingThreshold;
function float calculateTotal(float subtotal) {
// some math here that references taxRate
return calculatedTotal
}
rule "Apply free shipping"
when
Cart( $subtotal: subtotal )
Float( this >= freeShippingThreshold) from calculateTotal($subtotal)
then
// you get free shipping
end
I am trying to create some kind of a dut_error wrapper. Something that will take some arguments and construct them in a specific way to a dut_error.
I can't use a method to replace the calls to dut_error because to my understanding after check that ... then ... else can only come a dut_error (or dut_errorf). And indeed if I try to do something like:
my_dut_error(arg1: string, arg2: string) is {
dut_error("first argument is ", arg, " and second argument is ", arg2);
};
check that FALSE else my_dut_error("check1", "check2");
I get an error:
*** Error: Unrecognized exp
[Unrecognized expression 'FALSE else my_dut_error("check1", "check2")']
at line x in main.e
check that FALSE else my_dut_error("check1", "check2");
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
So I thought about defining a macro to simply do a textual replace from my wrapper to an actual dut_error:
define <my_dut_error'exp> "my_dut_error(<arg1'name>, <arg2'name>)" as {
dut_error("first argument is ", <arg1'name>, " and second argument is ", <arg2'name>)
};
But got the same error.
Then I read about the preprocessor directive #define so tried:
#define my_dut_error(arg1, arg2) dut_error("first argument is ", arg, " and second argument is ", arg2)
But that just gave a syntax error.
How can I define a pre-compiled textual replacement macro that takes arguments, similar to C?
The reason I want to do that is to achieve some sort of an "interface" to the dut_error so all errors have a consistent structure. This way, different people writing different errors will only pass the arguments necessary by that interface and internally an appropriate message will be created.
not sure i understood what you want to do in the wrapper, but perhaps you can achieve what you want by using the dut_error_struct.
it has set of api, which you can use as hooks (do something when the error is caught) and to query about the specific error.
for example:
extend dut_error_struct {
pre_error() is also {
if source_method_name() == "post_generate" and
source_struct() is a BLUE packet {
out("\nProblem in generation? ", source_location());
// do something for error during generation
};
write() is first {
if get_mesage() ~ "AHB Error..." {
ahb_monitor::increase_errors();
};
};
};
dut_error accepts one parameter, one string. but you can decide of a "separator", that will define two parts to the message.
e.g. - instruct people to write "XXX" in the message, before "first arg" and "second arg".
check that legal else dut_error("ONE thing", "XXX", "another thing");
check that x < 7 else dut_error("failure ", "XXX", "of x not 7 but is ", x);
extend dut_error_struct {
write() is first {
var message_parts := str_split(get_message(), "XXX");
if message_parts.size() == 2 {
out ("First part of message is ", message_parts[0],
"\nand second part of message is ", message_parts[1]
);
};
};
I could get pretty close to what I want using the dut_errorf method combined with a preprocessor directive defining the format string:
#define DUT_FORMAT "first argument is %s and second argument is %s"
check that FALSE else dut_errorf(DUT_FORMAT, "check1", "check2");
but I would still prefer a way that doesn't require this DUT_FORMAT directive and instead uses dut_error_struct or something similar.
I am trying to write a macro for debug print in the Nim language.
Currently this macro adds filename andline to the output by instantiationInfo().
import macros
macro debugPrint(msg: untyped): typed =
result = quote do:
let pos = instantiationInfo()
echo pos.filename, ":", pos.line, ": ", `msg`
proc hello() =
debugPrint "foo bar"
hello()
currently output:
debug_print.nim:9: foo bar
I would like to add the name of the procedure (or iterator) of the place where the macro was called.
desired output:
debug_print.nim:9(proc hello): foo bar
How can I get the name of procedure (or iterator) in Nim, like __func__ in C?
At runtime you can do getFrame().procname, but it only works with stacktrace enabled (not in release builds).
At compile-time surprisingly I can't find a way to do it. There is callsite() in macros module, but it doesn't go far enough. It sounds like something that might fit into the macros.LineInfo object.
A hacky solution would be to also use __func__ and parse that back into the Nim proc name:
template procName: string =
var name: cstring
{.emit: "`name` = __func__;".}
($name).rsplit('_', 1)[0]
building on answer from #def- but making it more robust to handle edge cases of functions containing underscores, and hashes containing trailing _N or not
also using more unique names as otherwise macro would fail if proc defines a variable name
import strutils
proc procNameAux*(name:cstring): string =
let temp=($name).rsplit('_', 2)
#CHECKME: IMPROVE; the magic '4' chosen to be enough for most cases
# EG: bar_baz_9c8JPzPvtM9azO6OB23bjc3Q_3
if temp.len>=3 and temp[2].len < 4:
($name).rsplit('_', 2)[0]
else:
# EG: foo_9c8JPzPvtM9azO6OB23bjc3Q
($name).rsplit('_', 1)[0]
template procName*: string =
var name2: cstring
{.emit: "`name2` = __func__;".}
procNameAux(name2)
proc foo_bar()=
echo procName # prints foo_bar
foo_bar()
NOTE: this still has some issues that trigger in complex edge cases, see https://github.com/nim-lang/Nim/issues/8212
I am trying to use inline if condition as follows:
topDisplay.text = topDisplay.text!.rangeOfString(".") ? "Sth for true" : "Sth for false"
The idea here is if there is "." in the topDisplay.text! then do something, if not, do something else. The method, rangeOfString, returns nil if no "." is found. So I am wondering is it possible to check nil within inline condition expression.
((btw, you might find out that I am trying to add "." button for calculator assignment in Stanford's online course, and to use only one line to implement this function as the hint describes))
So I am wondering is it possible to check nil within inline condition expression.
Sure. rangeOfString(".") != nil is a boolean expression which can
be used as the condition in the conditional expression:
topDisplay.text = topDisplay.text!.rangeOfString(".") != nil ? "Sth for true" : "Sth for false"
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
is object empty?
update: (id, data) ->
toUpdate = #find(id)
if toUpdate isnt {}
console.log "hi mom"
console.log toUpdate
toUpdate.setProperty(key, value) for own key, value of data
return toUpdate
find:(id) ->
result = record for record in #storage when record.id is id
return result or {}
Given the following Mocha tests
describe '#update', ->
it 'should return an updated record from a given id and data when the record exists', ->
boogie = createData()
archive = new Archive("Dog")
dog = archive.create(boogie)
result = archive.update(1, {name:"Chompie", age:1})
result.name.should.eql "Chompie"
result.age.should.eql 1
result.emotion.should.eql dog.emotion
it 'should return an updated record from a given id and data when the record does not exist', ->
boogie = createData()
archive = new Archive("Dog")
dog = archive.create(boogie)
result = archive.update(50, {name:"Chompie", age:1})
result.should.not.exist
The result is
Archive #update should return an updated record from a given id and data when the record exists: hi mom
{ id: 1,
validationStrategies: {},
name: 'Boogie',
age: 2,
emotion: 'happy' }
✓ Archive #update should return an updated record from a given id and data when the record exists: 1ms
Archive #update should return empty when the record does not exist: hi mom
{}
✖ 1 of 13 tests failed:
1) Archive #update should return empty when the record does not exist:
TypeError: Object #<Object> has no method 'setProperty'
...surprising, isnt it?
CoffeeScript's is (AKA ==) is just JavaScript's === and isnt (AKA !=) is just JavaScript's !==. So your condition:
if toUpdate isnt {}
will always be true since toUpdate and the object literal {} will never be the same object.
However, if #find could return a known "empty" object that was available in a constant, then you could use isnt:
EMPTY = {}
find: ->
# ...
EMPTY
and later:
if toUpdate isnt EMPTY
#...
For example, consider this simple code:
a = { }
b = { }
console.log("a is b: #{a is b}")
console.log("a isnt b: #{a isnt b}")
That will give you this in your console:
a is b: false
a isnt b: true
But this:
class C
EMPTY = { }
find: -> EMPTY
check: -> console.log("#find() == EMPTY: #{#find() == EMPTY}")
(new C).check()
will say:
#find() == EMPTY: true
Demo: http://jsfiddle.net/ambiguous/7JGdq/
So you need another way to check if toUpdate isn't empty. You could count the properties in toUpdate:
if (k for own k of toUpdate).length isnt 0
or you could use the special EMTPY constant approach outlined above. There are various other ways to check for an empty object, Ricardo Tomasi has suggested a few:
Underscore offers _.isEmpty which is basically the for loop approach with some special case handling and a short circuit.
Underscore also offers _.values so you could look at _(toUpdate).values().length. This calls map internally and that will be the native map function if available.
You could even go through JSON using JSON.stringify(toUpdate) is '{}', this seems a bit fragile to me and rather round about.
You could use Object.keys instead of the for loop: Object.keys(toUpdate).length isnt 0. keys isn't supported everywhere though but it will work with Node, up-to-date non-IE browsers, and IE9+.
Sugar also has Object.isEmpty and jQuery has $.isEmptyObject.
A short-circuiting for loop appears to be the quickest way to check emptiness:
(obj) ->
for k of toUpdate
return true
false
That assumes that you don't need own to avoid iterating over the wrong things. But given that this is just a test suite and that an emptiness test almost certainly won't be a bottle neck in your code, I'd go with whichever of Underscore, Sugar, or jQuery you have (if you need portability and have to deal with the usual browser nonsense), Object.keys(x).length if you know it will be available, and (k for own k of toUpdate).length if you don't have the libraries and have to deal with browser nonsense and aren't certain that toUpdate will be a simple object.