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make-broadcast-stream

make-broadcast-stream Function

Syntax:

make-broadcast-stream &rest streams → broadcast-stream

Arguments and Values:

stream—an output stream.

broadcast-stream—a broadcast stream.

Description:

Returns a broadcast stream.

Examples:

(setq a-stream (make-string-output-stream) 
      b-stream (make-string-output-stream)) → #<String Output Stream> 
(format (make-broadcast-stream a-stream b-stream) 
	"this will go to both streams") → NIL 
(get-output-stream-string a-stream) → "this will go to both streams" 

(get-output-stream-string b-stream) → "this will go to both streams"

Exceptional Situations:

Should signal an error of type type-error if any stream is not an output stream.

See Also:

broadcast-stream-streams

Expanded Reference: make-broadcast-stream​

Basic Usage​

make-broadcast-stream creates an output stream that sends output to all of its component streams simultaneously.

(let ((a (make-string-output-stream))
      (b (make-string-output-stream)))
  (let ((broadcast (make-broadcast-stream a b)))
    (write-string "hello to both" broadcast))
  (list (get-output-stream-string a)
        (get-output-stream-string b)))
=> ("hello to both" "hello to both")

Using with format​

(let ((s1 (make-string-output-stream))
      (s2 (make-string-output-stream)))
  (format (make-broadcast-stream s1 s2)
          "this will go to both streams")
  (list (get-output-stream-string s1)
        (get-output-stream-string s2)))
=> ("this will go to both streams" "this will go to both streams")

Discarding Output (No Component Streams)​

A broadcast stream with no components is a "bit bucket" -- all output is discarded.

(let ((s (make-broadcast-stream)))
  (write-string "discarded" s)
  (format s "also discarded ~D" 42)
  (output-stream-p s))
=> T

Three or More Streams​

Any number of output streams can be combined.

(let ((streams (loop repeat 3 collect (make-string-output-stream))))
  (let ((bc (apply #'make-broadcast-stream streams)))
    (write-string "triple" bc))
  (mapcar #'get-output-stream-string streams))
=> ("triple" "triple" "triple")