Re: Ruby quick reference arranged in ASCII sequence?

On Sat, Dec 15, 2012 at 5:40 PM, tamouse mailing lists
<[e-mail]> wrote:
> On Sat, Dec 15, 2012 at 9:26 AM, Eric Christopherson
> <[e-mail]> wrote:
>> On Sat, Dec 15, 2012 at 7:00 AM, Old Grantonian <[e-mail]> wrote:
>>> As a ruby beginner, I would be grateful for any links to a ruby
>>> reference that is arranged in ASCII sequence.
>> [...]
>>> For this line, I would like to find a reference that explains the
>>> following items in ASCII sequence:
>>>
>>> ?
>>> ==
>>> %s
>>> :
>>> \
>>> printf
>>>
>>> Probably all of these items would be explained in a good tutorial, but
>>> it might take hours to find them.
>>
>> You might try http://symbolhound.com to search for non-alphanumeric
>> things like those, along with the word Ruby to narrow things down.
>>
>
> I don't know where you'd find such a reference, but you could build
> one as you go.
>
> In the meantime, I know you asked for a reference, but the thing
> you're wondering about is this:
>
>     var = expr1 ? expr2 : expr3
>
> That's known as the "ternary" operator. if expr 1 is true, var gets
> the result of expr2, otherwise it gets the result of expr3. If you
> unpack this into more typical syntax, you get:
>
>     if expr1
>       var = expr2
>     else
>       var = expr3
>     end
>
> The second form is much clearer when reading code, but the first form
> saves quite a bit of space and typing.
>
> The next aspect is to look at the printf statements. These are
> actually a really non-ruby way of doing something, this looks a lot
> more like C, C++, or php.
>
> In ruby, everything (ALL THE THINGS!!) are objects. Objects are told
> what to do with their data by methods.
>
> last_name.length==0 ? printf(",") : printf("\"%s\",", last_name)
>
> So lets break this down.
>
>     last_name.length --- this is telling the object last_name to
> return it's length
>
>     == --- this is the equals comparison
>
> so
>     last_name.length == 0
>
> is asking if last_name is empty. Ruby has a better way of writing this:
>
>     last_name.empty?
>
> The empty? method simply asks exactly what the previous way was
> attempting to find out. empty? is implemented something like this:
>
>     def empty?
>       self.length == 0
>     end
>
> So why do that? Because this:
>
>     last_name.empty?
>
> is more readable than the other. It's a direct expression of what you
> want to know at that point.
>
> Now, onwards
>
>     printf(",")
>
> This starts to get into error territory. Just using this as it is is
> incorrect. Not that it would produce a run-time error -- it won't --
> however, it's a gross misunderstanding of the printf method. printf
> means "Print with formatting". If you aren't formatting anything,
> don't. Use print instead.
>
> The next part
>
>     printf("\"%s\","," last_name)
>
> is a slightly more legitimate use of printf, in that the variable
> last_name is being formatted as a quoted sting and printed.
>
> So all in all, what this
>
>     last_name.length==0 ? printf(",") : printf("\"%s\",", last_name)
>
> means, in pseudo code, is:
>
>   If the last name is empty,
>     just print a comma
>   Otherwise,
>     print the last name surrounded by double quotes
>       followed by a comma
>
> Now, that will all work. But it isn't idiomatic ruby.
>
>     print last_name.empty ? "," : "\"#{last_name}\","
>
> makes better use of ruby's expressiveness.
>
> Why learn idioms, you may ask?
>
> Simple, so you will understand the other speakers of the language you
> are trying to learn. If you write code solely by casting about for
> examples that might do what you want, and stop looking the moment you
> get close, just like your bookshelves that are all wobbly and falling
> over because you stopped looking for how to build them when you found
> a hammer and nails, your code will rot and fall over as well. And that
> might be okay.

Crikey, I forgot to explain the last bit:

the #{expr} notation inside a double quoted string means to substitute
the value of the expression at that point in the string, also known as
"interpolation". So:

    variable = "something"
    "this string includes the value of #{variable}"

would yield

    "this string includes the value of something"

You can put any valid ruby expression inside the braces:

    "this string includes the value of #{10 * 1024 / 3.1415}"

would yield

    "this string includes the value of 3259.5893681362404"