Single Equal Sign, Ambiguity

[ferbfletcher]

Why does AutoIt use "=" for both compare and for assignment?

Consider the following:

$x = 4

While ($x = 5)
ExitLoop
Wend

MsgBog("","",$x)

Now, what is the contents of $x ?


Many languages have a difference between assignment (=) and comparision (==)

AutoIt, however, uses (=) for both.

So, that While statement above could be read as
"while the contents of $x is equal to 5"  ... this would be false because $x is 4
-or-
it could be read as 
"while $x is commanded to take the value of 5" ... which would always be true because $x can always be commanded to take the value of 5.

Then, AFTER the while loop, $x might be 4 or it might be 5 ... depending on whether the (=) was taken to mean "compare" or "assign".

Of course, I can run the script easily enough and see the results for myself ... but this really does show the ambiguity of the equal sign in AutoIt.

 

[argumentum]

ConsoleWrite(Int("Hello" = "hello") & @CRLF)
ConsoleWrite(Int("Hello" == "hello") & @CRLF)

 

[SadBunny]

It's not ambiguous. AutoIt doesn't, for instance, support the "assignment operation is an expression that returns the assigned value" thing. When used in an expression it tests two values for some sort of equality, and when in an assignment command it assigns a value.

You didn't show any ambiguity, but you showed to two distinct ways of using the equals-sign.

Don't get me wrong, when I haven't coded in AutoIt for a long time I do that wrong all the time too. It isn't all that obvious...

[jchd]

ferbfletcher,

The = sign is nowhere ambiguous in AutoIt. All = sign in an expression is an assertion while all = sign separating a LHV (left hand variable) and an expression is an assignment.

Hence your example where the = sign is part of an expression is obviously an assertion. And this is a Good Thing™: look at how many zillion bugs C has called for by allowing = in tests, forcing the programmers to adopt the un-natural style if (3 == myvar) { ...

The use of an operator in distinct contexts is common in programming languages: for instance, C uses * to either mean either multiply or pointer, depending on context. Yet, noone barks.

[ferbfletcher]

Thanks.  When I said "ambiguous", I meant the exact same code "$x=something" can mean 2 different things based on where it is located (inside an if statement or standalone) ... not that AutoIt executes it in an unpredictable way.  Coming from C and PHP, this single equal sign is slightly confusing ... yet very simple, at the same time.

Edited May 21, 2015 by ferbfletcher

[jvanegmond]

Did you run into trouble because you expected you could assign variables inside an expression? Even in languages that support it, it's not something you see very often -- and personally every time I see it, I wonder if that's not something that would be better split onto a separate line. I'm honestly curious how you came to this idea. In the future, if you're learning a new language, memorize the operators documentation on the first day.

If you came from a Basic-variant language (and others), you'd be surprised at the double equals sign. So that's a very weak argument. You are correct to assert that many popular languages today do opt for a double equals sign. Perhaps if we were to build AutoIt from scratch, we'd probably reconsider this choice. Making that change now would break all existing AutoIt code ever written and the cost/benefit of that is simply not good enough to warrant a change.

Keep in mind that creating a programming language isn't easy. There's always some place where your chosen paradigms don't blend as perfectly as you'd want. What is easy is poking holes in languages that have gone through the growing pains. A good example is that we all love to make fun of JavaScript but actually improving the language is really hard and requires years of hard work.

[James]

Did you run into trouble because you expected you could assign variables inside an expression? Even in languages that support it, it's not something you see very often -- and personally every time I see it, I wonder if that's not something that would be better split onto a separate line. I'm honestly curious how you came to this idea. In the future, if you're learning a new language, memorize the operators documentation on the first day.

​In PHP I do this a lot:

if (($a = $result) !== false) {

}

 

[jchd]

Likewise in C[--|++]. Yet we're talking about AutoIt and it uses a distinct semantics for both = and == than some other languages.

The best way to recover peace of mind is to accept it or leave it.

[ferbfletcher]

Thank you, everyone, for your input!