Here’s another use of methods. Notice that when we send an array as a parameter, changes in the function do update the value to the caller.
Functions (and later methods) are defined with def. Parameters are given, without types of course. Default values may be provided. Note that when we send an integer, the method does not change the value sent.
case statement is similar to the C/C++/Java
switch, but more directly related to the similar (and superior) structures from Pascal and Ada. First, it assumes that each case ends where the next one starts, without needing a
break to terminate a case. Secondly, each case can be expressed rather generally, with a single value, a range of value, or a list containing some of each.
for loop is similar to the Python
for or the perl
foreach. Its basic operation is iterate over the contents of some collection. This may be an actual array or a range expression. A range expression is two numbers, surrounded by parens, and separated by either two dots or three. The three-dot form omits the last number from the range, while the two-dot version includes it. The three-dots version can be quite useful for creating a range of legal subscripts since the array size is not a legal subscript.
while loop is conventional, but it also has a postfix form.
Following from the previous tutorial on Conditional Logic in Ruby, look at this example:
# Let the user guess.
print "Enter heads or tails? "
hort = gets.chomp
unless hort == 'heads' || hort == 'tails'
print "I _said_ heads or tails. Can't you read?\n"
# Now toss the coin.
toss = if rand(2) == 1 then
print "Toss was ", toss, ".\n"
print "You Win!\n" if hort == toss
Some more amazing
unlesskeyword is like
if, but uses the opposite sense of the test: The code is run if the test is false.
- As with many things in Ruby,
ifmay look like a statement, but it is actually an expression, with a return value.
ifhas a postfix form where the condition comes last. This works with
This is the conventional use of the
if in perl. Notice that there is no need for curly braces (
}). The body of the
if ends with the appropriate keyword,
then word is generally optional, though you need it if you want to put start the body on the same line as the
if, the way the last statement does.
A parallel assignment sets several variables at once. All right sides are computed before any variable is assigned, so all right side values are computed with the old variable values. This is very convenient for swapping two values without using a temporary.
This version opens a file for writing, and writes its output to a file selected by the user. The second argument to open is the same as the second argument to a plain C fopen, except it will default to reading.
The object returned from open is class File.