abstract class IO

Overview

The IO class is the basis for all input and output in Crystal.

This class is inherited by types like File, Socket and IO::Memory and provides many useful methods for reading from and writing to an IO, like print, puts, gets and printf.

The only requirement for a type including the IO module is to define these two methods:

For example, this is a simple IO on top of a Bytes:

class SimpleSliceIO < IO
  def initialize(@slice : Bytes)
  end

  def read(slice : Bytes)
    slice.size.times { |i| slice[i] = @slice[i] }
    @slice += slice.size
    slice.size
  end

  def write(slice : Bytes) : Nil
    slice.size.times { |i| @slice[i] = slice[i] }
    @slice += slice.size
  end
end

slice = Slice.new(9) { |i| ('a'.ord + i).to_u8 }
String.new(slice) # => "abcdefghi"

io = SimpleSliceIO.new(slice)
io.gets(3) # => "abc"
io.print "xyz"
String.new(slice) # => "abcxyzghi"

Encoding

An IO can be set an encoding with the #set_encoding method. When this is set, all string operations (gets, gets_to_end, read_char, <<, print, puts printf) will write in the given encoding, and read from the given encoding. Byte operations (read, write, read_byte, write_byte, getb_to_end) never do encoding/decoding operations.

If an encoding is not set, the default one is UTF-8.

Mixing string and byte operations might not give correct results and should be avoided, as string operations might need to read extra bytes in order to get characters in the given encoding.

Defined in:

lib/libremiliacr/src/remilib/console/ansi.cr
lib/libremiliacr/src/remilib/extensions.cr
remiaudio/common.cr

Instance Method Summary

Instance Method Detail

def expectChunkType(chunkType : String, message : String | Nil = nil) : String | Nil #

Attempts to read a RIFF Chunk ID from the IO. The chunk ID must be equal to chunkType. If it is, this returns the chunk that was read, otherwise this raises an IO::Error.

If message is specified, then the error uses that as the message, otherwise it uses a more generic error message that lists what it found and the expected chunk name.


[View source]
def expectChunkType(chunkTypes : Array(String), message : String | Nil = nil) : String | Nil #

Attempts to read a RIFF Chunk ID from the IO. The chunk ID must be one of the chunk names listed in chunkTypes. If it is, this returns the chunk that was read, otherwise this raises an IO::Error.

If message is specified, then the error uses that as the message, otherwise it uses a more generic error message that lists what it found and the expected chunk name.


[View source]
def peekChar : Char | Nil #

Gets the next ::Char in this IO, or nil if there is none. The internal position is not changed.

The IO must support ::IO#pos and ::IO#pos=


[View source]
def readFourCC : String | Nil #

Attempts to read a "four CC" string from the IO, as used in RIFF formats. If four bytes cannot be read, this returns nil.


[View source]