[Pharo-users] Stream >> <<
raoknz at gmail.com
Tue Sep 10 08:54:56 EDT 2019
I think it's fair to say that #<< *is* a bug.
There does not seem to be any coherent description of what it means.
It's overloaded to mean *either* #nextPut: *or* #nextPutAll: *or*
something else, in some confusing ways.
CommandLineHandler #nextPutAll: (sent somewhere else)
Integer left shift (someone has been smoking too much
NonInteractiveTranscript #show: = locked #print:
SocketStream #putOn: (which may itself act like
#nextPut:, #nextPutAll:, #print,
put elements sans separators, or
Stream #putOn: (see above)
WriteStream either #nextPutAll: or #putOn:
Transcript #show: = locked #print:
ThreadSafeTranscript #show: = locked #print:
VTermOutputDriver2 #asString then #nextPutAll:
ZnHtmlOutputStream #asString then #nextPutAll:
SequenceableCollection class #streamContents:
As was once said about PL/I, #<< fills a much-needed gap.
When I see #print:, or #nextPut:, or #nextPutAll:, I know
what to expect. When I see #putOn:, I have in general no
idea what will happen. And when I see << it is worse.
One point of << is to imitate C++'s composition of outputs.
That might work, too, if only there were some agreement
about what #nextPutAll: returns. There is not. It might
return the receiver. It might return some other stream
related to the receiver. It might even return the collection
argument. So when you see
a << b << c
in general you not only do not have a clue what (a) is going
to do with (b) but you have no idea what object the message
<< c will be sent to.
Now let's see if we can puzzle out what
Array streamContents: [ :s | s << 10 << '10' << #(10 '10') ]
The output will be going to a WriteStream.
aWriteStream << anInteger
is not, but is like, aWriteStream print: anInteger.
So we add $1 and $0.
aWriteStream << aString
reduces to aWriteStream nextPutAll: aString.
So we add $1 and $0.
aWriteStream on anArray << anotherArray
reduces to aWriteStream nextPutAll: anotherArray.
So we add 10 and '10'.
Thus the result we get is
#($1 $0 $1 $0 10 '10').
What result we should *expect* from this muddle I cannot say.
If, on the other hand, you wrote explicitly
Array streamContents: [:stream |
stream print: 10; nextPutAll: '10'; nextPutAll: #(10 '10')]
you would have an easy time figuring out what to expect.
By the way, there is no standard definition of #show:, but in
other Smalltalk systems it's usually a variant of #nextPutAll:,
not a variant of #print:. There's no denying that locked output
is useful to have, but #show: is not perhaps the best name for it.
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