Programming languages have strict and mostly very compressed syntax. The origins of that are twofold.
First, actively used programming languages have a considerable history, and were started decades ago. Back then, screen space was limited, and, before that, there was little storage available for source code. Second, programmers have technically-oriented minds and like to endow abstract symbols with complex abstractions instead of using words to describe them. That's why, I guess, many programming languages heavily depend on correct usage of individual characters. Even as few characters as one may make a difference in program behavior as well as in whether program compiles.
Such caveats in different languages include:
- C++ templates. You can't write map<int,vector<int>> when you define a mapping from integers to arrays of integers, because C++ parsers thinks that >> as a bit-shift operator in an improper place. A correct program differs by a single space between the < signs.
- Makefile tabs. A rule body in the Unix Makefiles should be indented with a Tab. Spaces do not work. Being a software with more than 30 years of history, make had it fixed only a year ago.
- CSS delimiters. When you define a cascading style sheet, amd want to define the same block of style attributes for a certain class inside a certain tag, you write the selector as tag .class. It's just a space away from tag.class that defines the styles only for tag elements of class class.
Imagine how surprised I was when I realized that I made a variation of mistake #4 in my Ruby code today! Here's what it was about.
Ruby hash niceness
Named parameter is a way to specify function arguments at call by name (rather than by order, as in the standard function call notation).
Here you may find how the Named Parameter is implemented in various programming languages.
To emulate a Named Parameter Idiom, Ruby uses hashes and some syntax sugar. The last parameter of a function may be a hash, which maps from parameter names to values. Syntax sugar allows a programmer to write
This sugar is not unique to Ruby; Perl also supports it.
The :name notation specifies a symbolic constant, which effectively is an immutable string that is defined by only one ancillary character.
Such hashes and symbols seem as a very useful feature. It allows you to emulate DSL-s; here's an example of Ruby on Rails web framework routing configuration:
Until one day, after an hour of debugging you find yourself having written something like this:
See what's wrong here? Indeed, here's how the code of the function called might look like:
So, options[:attribute_check] should evaluate to false boolean value, but... :false is a totally different thing; it's an immutable string of five characters that evaluates to true instead! Just one colon that lurked into the code, and it made it behaving very wrong way.
Just like in a C-style typo, some expressions that are evaluated as true in boolean context look like those that are evaluated as false, and you should be careful with the borderline.
New named attribute definition style in Ruby
New named attribute passing style was not designed to address this problem. However, the abundance of colons in such a code makes it look worrying in case there is a mistake like the above:
You see that the mistake is easy to spot, because the conjunction between the name and the parameter value is so ugly, that it immediately draws attention. However, if you actually need to specify symbol as a value, then you'll have to look ugly with this style.
Moreover, you can't erase the space between the parameter name and value, because for this code:
Ruby parser will think that it's false method in an attribute_check object, as :: is a scope resolution operator, just like in C++. Space matters again, as in typo #1 desccribed above.
People say that this style resembles that of C# or JSON. So, maybe, it is a good idea to migrate to it. Only two things prevent me from doing this so far: it's not portable to previous version of Ruby, 1.8 (though it slowly becomes obsolete), and I find the old style look much more cute :-)
This was yet another typo that makes our programs behave differently than we expect them to. And again, it was just one character that breaks the expected behavior of if statements that implicitly convert the condition to boolean type. Unfortunately, while the new Ruby named parameter syntactic sugar could help, it sometimes looks even worse to me.
I hope this post will help you avoid the similar mistake if you code in Ruby.
I would like to end with a joke about a mythical C++ programmer leaving hist last commit after having been fired:
Happy debugging to you, indeed!
Author Paul Shved
Modified January 10, 2012
License CC BY-SA 3.0