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I'm working on setting up configuration files in AngularJS. Is it possible to create a factory in AngularJS whose key cannot be overwritten? For example, I can set up a constant like this, which cannot be overwritten
module.constant('animals', {"cat": "meow", "dog": "woof"});
But I'd like to do something like this that allows for overwritten values but not the factory itself
module.value('catSound','meow')
.value('dogSound','woof')
.factory('animals', ['catSound','dogSound', function(catSound, dogSound) {
return {
"cat": catSound,
"dog": dogSound
}
});
The above factory can be overwritten allowing for another piece of code to have module.factory('animals',function(){ return 7 }) and break everything. However, as a factory, the individual values can (and should) be overwritable, so I should be able to assign module.value('catSound','hiss') and have things still work as expected.
I've tried injecting into constants, but as far as I've been able to understand that isn't possible. How can I prevent my factory declaration from being overwritten? I realize that constant probably isn't the correct term when describing what I want, but I do want the factory's function definition to be constant.
Everything is mutable in javascript, so setting up something like this is tricky and never completely fail-safe. I've looked around in the angular code and found no evidence of any attempt at a protection mechanism like you seem to be asking for.
My advise would be to just live with the risk. It's not worth trying to protect yourself other than with tests and nice long names. I assume you've been bitten once, but I think the chances are quite low, unless you define factories with very short names.
I'm writing a web application (in Python, not that it matters). One of the features is that people can leave comments on things. I have a class for comments, basically like so:
class Comment:
user = ...
# other stuff
where user is an instance of another class,
class User:
name = ...
# other stuff
And of course in my template, I have
<div>${comment.user.name}</div>
Problem: Let's say I allow people to post comments anonymously. In that case comment.user is None (undefined), and of course accessing comment.user.name is going to raise an error. What's the best way to deal with that? I see three possibilities:
Use a conditional in the template to test for that case and display something different. This is the most versatile solution, since I can change the way anonymous comments are displayed to, say, "Posted anonymously" (instead of "Posted by ..."), but I've often been told that templates should be mindless display machines and not include logic like that. Also, other people might wind up writing alternate templates for the same application, and I feel like I should be making things as easy as possible for the template writer.
Implement an accessor method for the user property of a Comment that returns a dummy user object when the real user is undefined. This dummy object would have user.name = 'Anonymous' or something like that and so the template could access it and print its name with no error.
Put an actual record in my database corresponding to a user with user.name = Anonymous (or something like that), and just assign that user to any comment posted when nobody's logged in. I know I've seen some real-world systems that operate this way. (phpBB?)
Is there a prevailing wisdom among people who write these sorts of systems about which of these (or some other solution) is the best? Any pitfalls I should watch out for if I go one way vs. another? Whoever gives the best explanation gets the checkmark.
I'd go with the first option, using an if switch in the template.
Consider the case of localization: You'll possibly have different templates for each language. You can easily localize the "anonymous" case in the template itself.
Also, the data model should have nothing to do with the output side. What would you do in the rest of the code if you wanted to test whether a user has a name or not? Check for == 'Anonymous' each time?
The template should indeed only be concerned with outputting data, but that doesn't mean it has to consist solely of output statements. You usually have some sort of if user is logged in, display "Logout", otherwise display "Register" and "Login" case in the templates. It's almost impossible to avoid these.
Personally, I like for clean code, and agree that templates should not have major logic. So in my implementations I make sure that all values have "safe" default values, typically a blank string, pointer to a base class or equivalent. That allows for two major improvements to the code, first that you don't have to constantly test for null or missing values, and you can output default values without too much logic in your display templates.
So in your situation, making a default pointer to a base value sounds like the best solution.
Your 3rd option: Create a regular User entity that represents an anonymous user.
I'm not a fan of None for database integrity reasons.
One thing I've sometimes wondered is which is the better style out of the two shown below (if any)? Is it better to return immediately if a guard condition hasn't been satisfied, or should you only do the other stuff if the guard condition is satisfied?
For the sake of argument, please assume that the guard condition is a simple test that returns a boolean, such as checking to see if an element is in a collection, rather than something that might affect the control flow by throwing an exception. Also assume that methods/functions are short enough not to require editor scrolling.
// Style 1
public SomeType aMethod() {
SomeType result = null;
if (!guardCondition()) {
return result;
}
doStuffToResult(result);
doMoreStuffToResult(result);
return result;
}
// Style 2
public SomeType aMethod() {
SomeType result = null;
if (guardCondition()) {
doStuffToResult(result);
doMoreStuffToResult(result);
}
return result;
}
I prefer the first style, except that I wouldn't create a variable when there is no need for it. I'd do this:
// Style 3
public SomeType aMethod() {
if (!guardCondition()) {
return null;
}
SomeType result = new SomeType();
doStuffToResult(result);
doMoreStuffToResult(result);
return result;
}
Having been trained in Jackson Structured Programming in the late '80s, my ingrained philosophy was always "a function should have a single entry-point and a single exit-point"; this meant I wrote code according to Style 2.
In the last few years I have come to realise that code written in this style is often overcomplex and hard to read/maintain, and I have switched to Style 1.
Who says old dogs can't learn new tricks? ;)
Style 1 is what the Linux kernel indirectly recommends.
From https://www.kernel.org/doc/Documentation/process/coding-style.rst, chapter 1:
Now, some people will claim that having 8-character indentations makes
the code move too far to the right, and makes it hard to read on a
80-character terminal screen. The answer to that is that if you need
more than 3 levels of indentation, you're screwed anyway, and should fix
your program.
Style 2 adds levels of indentation, ergo, it is discouraged.
Personally, I like style 1 as well. Style 2 makes it harder to match up closing braces in functions that have several guard tests.
I don't know if guard is the right word here. Normally an unsatisfied guard results in an exception or assertion.
But beside this I'd go with style 1, because it keeps the code cleaner in my opinion. You have a simple example with only one condition. But what happens with many conditions and style 2? It leads to a lot of nested ifs or huge if-conditions (with || , &&). I think it is better to return from a method as soon as you know that you can.
But this is certainly very subjective ^^
Martin Fowler refers to this refactoring as :
"Replace Nested Conditional with Guard Clauses"
If/else statements also brings cyclomatic complexity. Hence harder to test cases. In order to test all the if/else blocks you might need to input lots of options.
Where as if there are any guard clauses, you can test them first, and deal with the real logic inside the if/else clauses in a clearer fashion.
If you dig through the .net-Framework using .net-Reflector you will see the .net programmers use style 1 (or maybe style 3 already mentioned by unbeli).
The reasons are already mentioned by the answers above. and maybe one other reason is to make the code better readable, concise and clear.
the most thing this style is used is when checking the input parameters, you always have to do this if you program a kind of frawework/library/dll.
first check all input parameters than work with them.
It sometimes depends on the language and what kinds of "resources" that you are using (e.g. open file handles).
In C, Style 2 is definitely safer and more convenient because a function has to close and/or release any resources that it obtained during execution. This includes allocated memory blocks, file handles, handles to operating system resources such as threads or drawing contexts, locks on mutexes, and any number of other things. Delaying the return until the very end or otherwise restricting the number of exits from a function allows the programmer to more easily ensure that s/he properly cleans up, helping to prevent memory leaks, handle leaks, deadlock, and other problems.
In C++ using RAII-style programming, both styles are equally safe, so you can pick one that is more convenient. Personally I use Style 1 with RAII-style C++. C++ without RAII is like C, so, again, Style 2 is probably better in that case.
In languages like Java with garbage collection, the runtime helps smooth over the differences between the two styles because it cleans up after itself. However, there can be subtle issues with these languages, too, if you don't explicitly "close" some types of objects. For example, if you construct a new java.io.FileOutputStream and do not close it before returning, then the associated operating system handle will remain open until the runtime garbage collects the FileOutputStream instance that has fallen out of scope. This could mean that another process or thread that needs to open the file for writing may be unable to until the FileOutputStream instance is collected.
Although it goes against best practices that I have been taught I find it much better to reduce the nesting of if statements when I have a condition such as this. I think it is much easier to read and although it exits in more than one place it is still very easy to debug.
I would say that Style1 became more used because is the best practice if you combine it with small methods.
Style2 look a better solution when you have big methods. When you have them ... you have some common code that you want to execute no matter how you exit. But the proper solution is not to force a single exit point but to make the methods smaller.
For example if you want to extract a sequence of code from a big method, and this method has two exit points you start to have problems, is hard to do it automatically. When i have a big method written in style1 i usually transform it in style2, then i extract methods then in each of them i should have Style1 code.
So Style1 is best but is compatible with small methods.
Style2 is not so good but is recommended if you have big methods that you don't want, have time to split.
I prefer to use method #1 myself, it is logically easier to read and also logically more similar to what we are trying to do. (if something bad happens, exit function NOW, do not pass go, do not collect $200)
Furthermore, most of the time you would want to return a value that is not a logically possible result (ie -1) to indicate to the user who called the function that the function failed to execute properly and to take appropriate action. This lends itself better to method #1 as well.
I would say "It depends on..."
In situations where I have to perform a cleanup sequence with more than 2 or 3 lines before leaving a function/method I would prefer style 2 because the cleanup sequence has to be written and modified only once. That means maintainability is easier.
In all other cases I would prefer style 1.
Number 1 is typically the easy, lazy and sloppy way. Number 2 expresses the logic cleanly. What others have pointed out is that yes it can become cumbersome. This tendency though has an important benefit. Style #1 can hide that your function is probably doing too much. It doesn't visually demonstrate the complexity of what's going on very well. I.e. it prevents the code from saying to you "hey this is getting a bit too complex for this one function". It also makes it a bit easier for other developers that don't know your code to miss those returns sprinkled here and there, at first glance anyway.
So let the code speak. When you see long conditions appearing or nested if statements it is saying that maybe it would be better to break this stuff up into multiple functions or that it needs to be rewritten more elegantly.
What is the best practice/coding standard with regard to the "this" scope is AS3? Is there one? I feel it really helps with standardization and my readability, but sometimes it seems like "too much".
For instance, is the use of "this" in the following really necessary (I know it works without "this")?:
private var _item:Object;
private var selectedItem:Object;
public function set item(value:Object):void
{
this._item = value;
if (this._item["label"] == "doodad")
this.selectedItem = value;
}
public function set item(value:Object):void
{
return this._item;
}
"this" is not required unless you want to prevent naming conflicts between locally scoped variables (method params for instance) and instance variables.
In your example you are already using an underscore to mark a private variable, so it's an extra reason not to use "this" since you are really saying twice the same thing.
It certainly isn't necessary, but I agree that it can help with readability. Since I work more in more dynamic languages (e.g. Perl and Python), such conventions can be vital for quickly determining where variables and functions are scoped/located. If this convention works for you, I don't think it's a bad thing, per se.
Thus said, I've spent hours reformatting code which contained awkward conventions which impeded readability.
For example: one person I worked with wrote all assignments like this:
var foo:String= "bar";
This was irritating (I prefer " = " so I can clearly see the operator), and I spent a lot of time cleaning up thousands of lines of code I had to maintain. His convention (which, though we argued about several times, he refused to compromise on) tended to impede my work.
Strive for unity w/others working with you. If they need to support your code and find this aggravating, it's likely not worth it to leave it in. If you don't expect anyone to work directly with the source, use conventions which help you understand your code and document (somewhere) what they mean.
If you're working in a team, stick with the coding conventions of the team.
But personally, I find explicit use of "this", when not required for disambiguation, overkill that negatively affects readability in a statically typed language like AS3 (dynamic languages are another story!).
A class should only really have one responsibility so generally there shouldn't be too many properties on it. Inside a method you generally deal with three types of variables: temporary local variables, method parameters, and properties. Methods shouldn't be too long, so it should be easy to spot the difference between the three types - if it's not defined locally and hasn't been passed as a parameter, then it's a property. If the whole method doesn't fit on your screen then it's probably too long!
I only use "this" when needed to disambiguate between a property and a parameter with the same name.
I prefer not to use "this" too much, but sometimes do in Eclipse, just to get autocompletion (probably the worst reason to do it!)
Would make more sense if your example was:
public function set item(_item:Object):void
{
this._item = _item;
if (this._item["label"] == "doodad")
this.selectedItem = this._item;
}
Similar to Is hard-coding literals ever acceptable?, but I'm specifically thinking of "magic strings" here.
On a large project, we have a table of configuration options like these:
Name Value
---- -----
FOO_ENABLED Y
BAR_ENABLED N
...
(Hundreds of them).
The common practice is to call a generic function to test an option like this:
if (config_options.value('FOO_ENABLED') == 'Y') ...
(Of course, this same option may need to be checked in many places in the system code.)
When adding a new option, I was considering adding a function to hide the "magic string" like this:
if (config_options.foo_enabled()) ...
However, colleagues thought I'd gone overboard and objected to doing this, preferring the hard-coding because:
That's what we normally do
It makes it easier to see what's going on when debugging the code
The trouble is, I can see their point! Realistically, we are never going to rename the options for any reason, so about the only advantage I can think of for my function is that the compiler would catch any typo like fo_enabled(), but not 'FO_ENABLED'.
What do you think? Have I missed any other advantages/disadvantages?
If I use a string once in the code, I don't generally worry about making it a constant somewhere.
If I use a string twice in the code, I'll consider making it a constant.
If I use a string three times in the code, I'll almost certainly make it a constant.
if (config_options.isTrue('FOO_ENABLED')) {...
}
Restrict your hard coded Y check to one place, even if it means writing a wrapper class for your Map.
if (config_options.isFooEnabled()) {...
}
Might seem okay until you have 100 configuration options and 100 methods (so here you can make a judgement about future application growth and needs before deciding on your implementation). Otherwise it is better to have a class of static strings for parameter names.
if (config_options.isTrue(ConfigKeys.FOO_ENABLED)) {...
}
I realise the question is old, but it came up on my margin.
AFAIC, the issue here has not been identified accurately, either in the question, or the answers. Forget about 'harcoding strings" or not, for a moment.
The database has a Reference table, containing config_options. The PK is a string.
There are two types of PKs:
Meaningful Identifiers, that the users (and developers) see and use. These PKs are supposed to be stable, they can be relied upon.
Meaningless Id columns which the users should never see, that the developers have to be aware of, and code around. These cannot be relied upon.
It is ordinary, normal, to write code using the absolute value of a meaningful PK IF CustomerCode = "IBM" ... or IF CountryCode = "AUS" etc.
referencing the absolute value of a meaningless PK is not acceptable (due to auto-increment; gaps being changed; values being replaced wholesale).
.
Your reference table uses meaningful PKs. Referencing those literal strings in code is unavoidable. Hiding the value will make maintenance more difficult; the code is no longer literal; your colleagues are right. Plus there is the additional redundant function that chews cycles. If there is a typo in the literal, you will soon find that out during Dev testing, long before UAT.
hundreds of functions for hundreds of literals is absurd. If you do implement a function, then Normalise your code, and provide a single function that can be used for any of the hundreds of literals. In which case, we are back to a naked literal, and the function can be dispensed with.
the point is, the attempt to hide the literal has no value.
.
It cannot be construed as "hardcoding", that is something quite different. I think that is where your issue is, identifying these constructs as "hardcoded". It is just referencing a Meaningfull PK literally.
Now from the perspective of any code segment only, if you use the same value a few times, you can improve the code by capturing the literal string in a variable, and then using the variable in the rest of the code block. Certainly not a function. But that is an efficiency and good practice issue. Even that does not change the effect IF CountryCode = #cc_aus
I really should use constants and no hard coded literals.
You can say they won't be changed, but you may never know. And it is best to make it a habit. To use symbolic constants.
In my experience, this kind of issue is masking a deeper problem: failure to do actual OOP and to follow the DRY principle.
In a nutshell, capture the decision at startup time by an appropriate definition for each action inside the if statements, and then throw away both the config_options and the run-time tests.
Details below.
The sample usage was:
if (config_options.value('FOO_ENABLED') == 'Y') ...
which raises the obvious question, "What's going on in the ellipsis?", especially given the following statement:
(Of course, this same option may need to be checked in many places in the system code.)
Let's assume that each of these config_option values really does correspond to a single problem domain (or implementation strategy) concept.
Instead of doing this (repeatedly, in various places throughout the code):
Take a string (tag),
Find its corresponding other string (value),
Test that value as a boolean-equivalent,
Based on that test, decide whether to perform some action.
I suggest encapsulating the concept of a "configurable action".
Let's take as an example (obviously just as hypthetical as FOO_ENABLED ... ;-) that your code has to work in either English units or metric units. If METRIC_ENABLED is "true", convert user-entered data from metric to English for internal computation, and convert back prior to displaying results.
Define an interface:
public interface MetricConverter {
double toInches(double length);
double toCentimeters(double length);
double toPounds(double weight);
double toKilograms(double weight);
}
which identifies in one place all the behavior associated with the concept of METRIC_ENABLED.
Then write concrete implementations of all the ways those behaviors are to be carried out:
public class NullConv implements MetricConverter {
double toInches(double length) {return length;}
double toCentimeters(double length) {return length;}
double toPounds(double weight) {return weight;}
double toKilograms(double weight) {return weight;}
}
and
// lame implementation, just for illustration!!!!
public class MetricConv implements MetricConverter {
public static final double LBS_PER_KG = 2.2D;
public static final double CM_PER_IN = 2.54D
double toInches(double length) {return length * CM_PER_IN;}
double toCentimeters(double length) {return length / CM_PER_IN;}
double toPounds(double weight) {return weight * LBS_PER_KG;}
double toKilograms(double weight) {return weight / LBS_PER_KG;}
}
At startup time, instead of loading a bunch of config_options values, initialize a set of configurable actions, as in:
MetricConverter converter = (metricOption()) ? new MetricConv() : new NullConv();
(where the expression metricOption() above is a stand-in for whatever one-time-only check you need to make, including looking at the value of METRIC_ENABLED ;-)
Then, wherever the code would have said:
double length = getLengthFromGui();
if (config_options.value('METRIC_ENABLED') == 'Y') {
length = length / 2.54D;
}
// do some computation to produce result
// ...
if (config_options.value('METRIC_ENABLED') == 'Y') {
result = result * 2.54D;
}
displayResultingLengthOnGui(result);
rewrite it as:
double length = converter.toInches(getLengthFromGui());
// do some computation to produce result
// ...
displayResultingLengthOnGui(converter.toCentimeters(result));
Because all of the implementation details related to that one concept are now packaged cleanly, all future maintenance related to METRIC_ENABLED can be done in one place. In addition, the run-time trade-off is a win; the "overhead" of invoking a method is trivial compared with the overhead of fetching a String value from a Map and performing String#equals.
I believe that the two reasons you have mentioned, Possible misspelling in string, that cannot be detected until run time and the possibility (although slim) of a name change would justify your idea.
On top of that you can get typed functions, now it seems you only store booleans, what if you need to store an int, a string etc. I would rather use get_foo() with a type, than get_string("FOO") or get_int("FOO").
I think there are two different issues here:
In the current project, the convention of using hard-coded strings is already well established, so all the developers working on the project are familiar with it. It might be a sub-optimal convention for all the reasons that have been listed, but everybody familiar with the code can look at it and instinctively knows what the code is supposed to do. Changing the code so that in certain parts, it uses the "new" functionality will make the code slightly harder to read (because people will have to think and remember what the new convention does) and thus a little harder to maintain. But I would guess that changing over the whole project to the new convention would potentially be prohibitively expensive unless you can quickly script the conversion.
On a new project, symbolic constants are the way IMO, for all the reasons listed. Especially because anything that makes the compiler catch errors at compile time that would otherwise be caught by a human at run time is a very useful convention to establish.
Another thing to consider is intent. If you are on a project that requires localization hard coded strings can be ambiguous. Consider the following:
const string HELLO_WORLD = "Hello world!";
print(HELLO_WORLD);
The programmer's intent is clear. Using a constant implies that this string does not need to be localized. Now look at this example:
print("Hello world!");
Here we aren't so sure. Did the programmer really not want this string to be localized or did the programmer forget about localization while he was writing this code?
I too prefer a strongly-typed configuration class if it is used through-out the code. With properly named methods you don't lose any readability. If you need to do conversions from strings to another data type (decimal/float/int), you don't need to repeat the code that does the conversion in multiple places and can cache the result so the conversion only takes place once. You've already got the basis of this in place already so I don't think it would take much to get used to the new way of doing things.