From: Quintus <quintus@...>
Date: 2012-09-30T06:45:08+09:00
Subject: Re: general newbie qustion

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Am Sun, 30 Sep 2012 05:44:58 +0900
schrieb George Spak <lists@ruby-forum.com>:

> Justin T. wrote in post #1078043:
> > Put simply:
> >
> > "print x" will print just the letter x.
> > "print #{x}" parses out whatever the variable x is.
>=20
> Ah that makes sense.  Much appreciate the help.  Unfortunately, the
> docs are of little halp.  This must be buried deep in them.

It=E2=80=99s not correct.=20

x =3D 6
print x

This will print out the number 6, which is the current value of x. To
get the letter x, you want

print "x"

. That being said, #{} simply is a so-called string interpolation. These
two statements are basically equal:

str =3D "x is " + x.to_s + "!"
str =3D "x is #{x}!"

There are some subtle differences between them, namely regarding the
number of string objects created. It is generally considered good
coding practive using string interpolation if you don=E2=80=99t have a reas=
on
to do otherwise. Note that #{} can perfectly contain any valid Ruby
expression; if you want to push it to its limits, you can even define a
class inside it. Whatever the expression returns, will be converted to
a string using the #to_s method (which in the case of strings happens
to return the string itself). In contrast to this, the plus expression
wants to use its argument as-is and won=E2=80=99t try to call #to_s on it.
Compare:

x =3D 6
str =3D "x is #{x}"
str =3D "x is " + x

While the former will work as expected (calling Fixnum#to_s, which
returns the string "6"), the latter crashes with a TypeError, because
you tried to combine a number with a string. Chaining is not the same
as interpolation.

Vale,
Marvin


--=20
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