aist: переводы

→produces:

→produces:

→The code in the block (puts "In the block") is executed twice, once for each call to yield.

→Here we ask an array to call the block once for each of its elements. Then, object 5 calls a block five times. Rather than use for loops, in Ruby we can ask the number 3 to call a block, passing in successive values until it reaches 6. Finally, the range of characters from a to e invokes a block using the method each.

→Many of the looping constructs that are built into languages such as C and Java are simply method calls in Ruby, with the methods invoking the associated block zero or more times:

→produces:

→Code blocks are used throughout the Ruby library to implement iterators, which are methods that return successive elements from some kind of collection, such as an array:

→cat dog horse *****3456abcde

→print line

→line = gets

→You have many ways to read input into your program. Probably the most traditional is to use the routine gets, which returns the next line from your program’s standard input stream:

→In this example, the format string "Number: %5.2f,\nString: %s\n" tells printf to substitute in a floating-point number (with a minimum of five characters, two after the decimal point) and a string. Notice the newlines (\n) embedded in the string; each moves the output onto the next line.

→Ruby comes with a comprehensive I/O library. However, in most of the examples in this book, we’ll stick to a few simple methods. We’ve already come across two methods that do output: puts writes its arguments with a newline after each; print also writes its arguments but with no newline. Both can be used to write to any I/O object, but by default they write to standard output.

→Reading and ’Riting

→Because gets returns nil when it reaches the end of input, you can use its return value in a loop condition. Notice that here the condition to the while is an assignment: we store whatever gets returns into the variable line and then test to see whether that returned value was nil or false before continuing:

→Another output method we use a lot is printf, which prints its arguments under the control of a format string (just like printf in C or Perl):

→produces:

→printf("Number: %5.2f,\nString: %s\n", 1.23, "hello")

→Often, the arguments to a program are the names of files that you want to process. In this case, you can use a second technique: the variable ARGF is a special kind of I/O object that acts like all the contents of all the files whose names are passed on the command line (or standard input if you don’t pass any filenames). We’ll look at that some more on page 342.

→That’s it. We’ve finished our lightning-fast tour of some of the basic features of Ruby. We took a look at objects, methods, strings, containers, and regular expressions; saw some simple control structures; and looked at some rather nifty iterators. We hope this chapter has given you enough ammunition to be able to attack the rest of this book. Time to move on and move up—up to a higher level. Next, we’ll be looking at classes and objects, things that are at the same time both the highest-level constructs in Ruby and the essential underpinnings of the entire language.