Coding style of "if" statements

Question

Lately I've been noticing the style of some programmers who write "if" statements backwards. That is, in the test they put the constant value first and then the variable that they are testing second. So for example they write:

bar = foo();
if (MY_CONSTANT == bar) {
    /*  then do something */
}

To me, this makes code somewhat difficult to read. Since we are really talking about testing the value of the variable "bar" and not all variables that are equal to "MY_CONSTANT", I always put the variable first. Its sort of a unspoken grammar.

Anyhow, I see that some programmers ALWAYS do this in the opposite order. Further, I've only noticed this in the past few years. I've been programming in C for over 25 years and I've not seen this until, say, about the last 4 years or so. So my question is:

Is there a reason people are doing this and if so what is it? Is this a common standard in some languages, or projects, or is it taught in some universities? or is that just a few people trying to be different?

@vlad_tepesch explains why this style arose; but using it or not is primarily a question of personal opinion and style. — MaxVT, Apr 19 '16 at 15:44
Yoda-conditions not using you should. Ancient they are and modern compiler warn will for normal order already. — too honest for this site, Apr 19 '16 at 15:55
I don't think that it is all that recent. The university connection might explain why it perpetuates. Professors get tired of dealing with the same bug again and again, and the students making this bug are not the sorts likely to heed compiler warnings. Teaching the students to write it this way could save professors a little bit of time debugging student's code. — John Coleman, Apr 19 '16 at 15:56
@JohnColeman: Such code is more and more refused in a professional environment like companies, because compilers will warn about them since >10 years. Teaching students to use them is the wrong approach. Much simpler and more to common practice is to refuse code which generates diagnostics with common warnings enabled. It is more likely the prof once learned it that way and just keeps the habbit. Sadly, most professors don't like learning new tricks if they are not really necessary for their field of interest. — too honest for this site, Apr 19 '16 at 16:06
I've never seen Yodas refused. I actually prefer them to 'normal' construction that occasionally pushes the actual condition off the rhs of my edit/debugger window because it's a check on the result of some system call with 13 parameters. — Martin James, Apr 19 '16 at 16:19

vlad_tepesch · Accepted Answer · 2016-04-19T15:58:06.173

19

This is called "Yoda-Style" (or "Yoda conditions" or "Yoda notation") and should prevent you from accidentally writing

if (bar = MY_CONSTANT) {
    /*  then do something */
}

since

if (MY_CONSTANT = bar) {
    /*  then do something */
}

would trigger a compiler error.

The name is derived from the uncommon twisted sentence construction the Star Wars character Yoda is also using.

In my opinion using "Yoda-Style" makes understanding of code harder because it is against the normal sentence construction rules. Also code quality checker (or as mentioned in the comments maybe even the compiler itself) should complain about such assignments anyway, so that (imho) there is no good reason to obfuscate your code.

edited Apr 19 '16 at 15:58

answered Apr 19 '16 at 15:43

vlad_tepesch

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i was hoping the answer to this would be something of greater value. – HazirBot Apr 19 '16 at 15:44
2

Which, by the way, is one of the most inane reasons to do this, because competent compilers (or linters) warn about assignments in conditions. – Apr 19 '16 at 15:44
2

@Rhymoid People tend to ignore compiler warnings. It's the only and the sufficient reason. BTW, as the construct is completely legal, there is no reason to a standard complying compiler to warn about it. – Eugene Sh. Apr 19 '16 at 15:45
2

@EugeneSh. You can't really ignore the warning anymore when you always `-Wall -Werror`, which should be the default for all production code. – Apr 19 '16 at 15:46
I believe there is no hit in readability here. In fact, I believe code checkers should recommend such a style.. – sjsam Apr 19 '16 at 15:46
3

@Rhymoid "should be" and "actually is" are usually two different beasts... – Eugene Sh. Apr 19 '16 at 15:47
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@EugeneSh., totally moot. Ignoring warnings is the same thing as ignoring safety when dealing with firearms and basically suits everybody since it helps eliminate stupid genes. – SergeyA Apr 19 '16 at 15:47
@SergeyA But still you have several safety layers when dealing with firearms. Just in case some of them are ignored.. People writing the code are not always the same ones running the build. – Eugene Sh. Apr 19 '16 at 15:49
@EugeneSh., when shooting for least commong denominator you will end up with least common denomitator. Suit yourself, but do not impose this on others. – SergeyA Apr 19 '16 at 15:51
_'This is called "Yoda-Style"'_ -> question: do you know _why_ is it called like this? I've never ever seen Yoda writing code... – ForceBru Apr 19 '16 at 15:51
1

@ForceBru, but have you seen Star Wars? :) – SergeyA Apr 19 '16 at 15:52
https://en.wikipedia.org/wiki/Yoda_conditions – Antti Haapala -- Слава Україні Apr 19 '16 at 15:53
OK. Thank you. I knew there was some insanity to this. I'm glad that the conventional wisdom is to frown upon it. – msundius Apr 19 '16 at 15:53
Their main use is in PHP nowadays. – Antti Haapala -- Слава Україні Apr 19 '16 at 15:53
@SergeyA, I've seen random bits of it, but never the whole thing... Does Yoda actually do programming? :D – ForceBru Apr 19 '16 at 15:53
1

@ForceBru, someone did program R2D2 after all :) :) :) – SergeyA Apr 19 '16 at 15:53
@ForceBru He is talking in a funny manner, rearranging the words order in sentences. – Eugene Sh. Apr 19 '16 at 15:54
Now I understand. Thanks and may the Force be with you! – ForceBru Apr 19 '16 at 15:56

score 8 · Answer 2 · answered Apr 19 '16 at 15:46

8

This is something of a best practice which someone thought best 15 years ago or so. Alleged benefit was that it would prevent someone from doing accidental assignments instead of comparison.

It was dubious back than, it is 100% moot nowadays since any compiler worth using will warn about assignment in branch operator, but hordes of lemmings still copy best practice without even thinking what it means or what it is for.

answered Apr 19 '16 at 15:46

SergeyA

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I routinely, intentionally, perform assignments in conditionals, particularly for `bool`s,, ie `if ((myBool=SomeBoolFunc()) == true){ // do stuff }else{ // do other stuff } // now I can return/use myBool without explicit assignment`. It saves me 2 lines for assigning the `bool` whether true or false (`if true, myBool = true, else myBool = false;`). I'm getting the consensus from these answers/comments that's considered bad practice? – yano Apr 19 '16 at 16:19
@yano, compiler will sugges parenthis around this assignment. Not a big deal. – SergeyA Apr 19 '16 at 16:23
ok yeah, that was the other thing. Pretty sure I've got warnings turned on and I don't think I've ever seen one warning me about this, but I always make sure to use parenthesis to do the assignment first and then the comparison. Thanks – yano Apr 19 '16 at 16:25
1

@yano i would consider it to be bad practice, since it hides side effects in an conditional that also may be lead to bugs if the condition is enhanced without reminding that short circuit evaluation may break your assignment. – vlad_tepesch Apr 25 '16 at 16:37
@yano As a second remark: comparing bool against bool constants is awkward. 1st it is illogical since the outcome is also a bool that then should be tested against a constant. 2nd: a value of 2 would also considered to be true, but what if `true` is internally considered to be 1 - so you are testing `1==2` (please note that language is C that in its basic form does not has a `bool` type - so someone must have written a define for this that relies on a integer data type) – vlad_tepesch Apr 25 '16 at 16:39

Coding style of "if" statements

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