- Pharo-users - lists.pharo.org

Re: [Pharo-users] can I do this with a stream or a format

by Richard O'Keefe

stream := WriteStream on: (String new: gifts size * "estimated size per gift" 10). "The number after #new: is the *initial* allocation; the stream will reallocate it as needed." gifts allButLastDo: [:each | stream nextPutAll: each; nextPutAll: ', ']. stream nextPutAll: 'and '; nextPutAll: gifts last. ^stream contents Using #allButLastDo: saves making a copy of (most of) gifts. How could you find out about these things? You want to join some strings, so you look for a "join" method in String and you will find join: aCollection ^ self class new: (aCollection size * self size) streamContents: [:stream | aCollection do: [:each | stream nextPutAll: each asString] separatedBy: [stream nextPutAll: self]] You might wonder if there is already something close to what you want, so you might enter "commas" into Spotter. If you did that, you would find Collection>>asCommaStringAnd so that the whole thing is very nearly gifts asCommaStringAnd Just as the concatenation selector #, works with most kinds of sequences, so building sequences up using a WriteStream works with most kinds of sequences. Let's work through a little example. We are just going to build up the string 'Quick' one character at a time. s := ''. s := s , 'Q'. "creates a new string holding 'Q'" s := s , 'u'. "creates a new string holding 'Qu'" s := s , 'i'. "creates a new string holding 'Qui'" s := s , 'c'. "creates a new string holding 'Quic'" s := s , 'k'. "creates a new string holding 'Quick'" You see that building a string of n characters will actually create n new strings, all but the last of which will be thrown away, taking O(n**2) time. Now let's use a stream. w := WriteStream on: (String new: 4). "Yes, I know that's too small." w nextPutAll: 'Q'. "The stream now holds 'Q...' in its buffer." w nextPutAll: 'u'. "The stream now holds 'Qu..' in its buffer." w nextPutAll: 'i'. "The stream now holds 'Qui.' in its buffer." w nextPutAll: 'c'. "The stream now holds 'Quic' in its buffer." s nextPutAll: 'k'. "There is no room left in the buffer, so the stream allocates a new buffer twice the size and copies the old one into it. Now it has 'Quic....' and it has room. The stream now holds 'Quick...' in its buffer." s := w contents. "We are asking for the defined elements of the buffer. This means s := buffer copyFrom: 1 to: w position." You see that building a string of n characters this way requires a minimum of two strings, the buffer and the final result. The buffer may be periodically resized, but growing by doubling means the average cost is still O(n). Let's time these to get an idea. Time millisecondsToRun: [ |s| s := ''. 1 to: 10000 do: [:i | s := s , i printString]. s size] => 124 Time millisecondsToRun: [ |w| w := WriteStream on: (String new: 10000). 1 to: 10000 do: [:i | w nextPutAll: i printString]. w contents size] => 7 This is exactly the reason that Java has both String and StringBuilder. The tragedy of Java (well, not the only one) is that they had the example of Smalltalk before them, showing very very clearly that the best way to handle object to text conversion is to use #printOn: as the primitive, not #printString, and they *still* went ahead and did the worse thing. (Ruby has even less excuse for privileging to_s.) There are quite a few books about Smalltalk available as free PDFs from the Pharo web site, a wonderful resource. The Blue Book (Smalltalk-80 The Language and its Implementation) describes streams in Chapter 12. On Fri, 17 May 2019 at 07:21, Roelof Wobben <r.wobben(a)home.nl> wrote: > Hello, > > Im testing all my solutions with critiz and can solve almost all problems, > > Only this one I cannot figure out. > > I have this code > > (gifts allButLast > inject: '' > into: [ :str :each | str , each , ', ' ]) , 'and ' , gifts last ] > > and critiz says I should use a stream . > > How can I make this work ? > > Roelof > > >

May 17, 2019

Re: [Pharo-users] can I do this with a stream or a format

by Roelof Wobben

May 16, 2019

Re: [Pharo-users] can I do this with a stream or a format

by Esteban Maringolo

Oh... the expected output was 'e1, e2, e3 and e4', I read "all" instead of "and". Now it makes sense. Esteban A. Maringolo On Thu, May 16, 2019 at 5:09 PM Roelof Wobben <r.wobben(a)home.nl> wrote: > and this is working > > String > streamContents: [ :stream | > gifts allButLast > do: [ :each | stream nextPutAll: each ] > separatedBy: [ stream > nextPut: $,; > space ]. > stream > nextPut: $,; > nextPutAll: ' and '; > nextPutAll: gifts last ] ] > > Thanks Estaban for the hint. > > Roelof > > > > Op 16-5-2019 om 21:51 schreef Roelof Wobben: > > I think this is better > > ^ String streamContents: [:stream | > > gifts > do: [:each | stream nextPutAll: each ] > separatedBy: [ stream nextPut: $,; space ] > stream nextputAll: 'all'; nextPut: ','; nextPut: gifts last] > > > > Op 16-5-2019 om 21:47 schreef Roelof Wobben: > > oke, and then do something like : > > stream := > > String streamContents: [:stream | gifts > do: [:each | stream nextPutAll: each ] > separatedBy: [ stream nextPut: $,; space ] > > > > stream nextputAll: 'all'; nextPut: ','; nextPut: gifts last > > ] > > stream nextputAll: 'all' > stream nextPut: ',' > stream nextPut: gifts last > > > Roelof > > > > Op 16-5-2019 om 21:30 schreef Esteban Maringolo: > > Maybe this is a better way to build what you want. > > String streamContents: [:stream | gifts > do: [:each | stream nextPutAll: each ] > separatedBy: [ stream nextPut: $,; space ] > ] > > Esteban A. Maringolo > > > On Thu, May 16, 2019 at 4:21 PM Roelof Wobben <r.wobben(a)home.nl> wrote: > >> Hello, >> >> Im testing all my solutions with critiz and can solve almost all problems, >> >> Only this one I cannot figure out. >> >> I have this code >> >> (gifts allButLast >> inject: '' >> into: [ :str :each | str , each , ', ' ]) , 'and ' , gifts last ] >> >> and critiz says I should use a stream . >> >> How can I make this work ? >> >> Roelof >> >> >> > > >

May 16, 2019

Re: [Pharo-users] can I do this with a stream or a format

by Roelof Wobben

May 16, 2019

Re: [Pharo-users] can I do this with a stream or a format

by Esteban Maringolo

Sorry, I misses the "all" part at the end (I don't see how that could add something, but if it's in the requirements...) Then it should be like this: String streamContents: [:stream | gifts allButLast do: [:each | stream nextPutAll: each ] separatedBy: [ stream nextPut: $,; space ]. stream nextPutAll: ' all, '; nextPutAll: gifts last]. Esteban A. Maringolo On Thu, May 16, 2019 at 4:52 PM Roelof Wobben <r.wobben(a)home.nl> wrote: > I think this is better > > ^ String streamContents: [:stream | > > gifts > do: [:each | stream nextPutAll: each ] > separatedBy: [ stream nextPut: $,; space ] > stream nextputAll: 'all'; nextPut: ','; nextPut: gifts last] > > > > Op 16-5-2019 om 21:47 schreef Roelof Wobben: > > oke, and then do something like : > > stream := > > String streamContents: [:stream | gifts > do: [:each | stream nextPutAll: each ] > separatedBy: [ stream nextPut: $,; space ] > > > > stream nextputAll: 'all'; nextPut: ','; nextPut: gifts last > > ] > > stream nextputAll: 'all' > stream nextPut: ',' > stream nextPut: gifts last > > > Roelof > > > > Op 16-5-2019 om 21:30 schreef Esteban Maringolo: > > Maybe this is a better way to build what you want. > > String streamContents: [:stream | gifts > do: [:each | stream nextPutAll: each ] > separatedBy: [ stream nextPut: $,; space ] > ] > > Esteban A. Maringolo > > > On Thu, May 16, 2019 at 4:21 PM Roelof Wobben <r.wobben(a)home.nl> wrote: > >> Hello, >> >> Im testing all my solutions with critiz and can solve almost all problems, >> >> Only this one I cannot figure out. >> >> I have this code >> >> (gifts allButLast >> inject: '' >> into: [ :str :each | str , each , ', ' ]) , 'and ' , gifts last ] >> >> and critiz says I should use a stream . >> >> How can I make this work ? >> >> Roelof >> >> >> > >

May 16, 2019

Re: [Pharo-users] can I do this with a stream or a format

by Roelof Wobben

May 16, 2019

Re: [Pharo-users] can I do this with a stream or a format

by Roelof Wobben

May 16, 2019

Re: [Pharo-users] can I do this with a stream or a format

by Roelof Wobben

May 16, 2019

Re: [Pharo-users] can I do this with a stream or a format

by Esteban Maringolo

Maybe this is a better way to build what you want. String streamContents: [:stream | gifts do: [:each | stream nextPutAll: each ] separatedBy: [ stream nextPut: $,; space ] ] Esteban A. Maringolo On Thu, May 16, 2019 at 4:21 PM Roelof Wobben <r.wobben(a)home.nl> wrote: > Hello, > > Im testing all my solutions with critiz and can solve almost all problems, > > Only this one I cannot figure out. > > I have this code > > (gifts allButLast > inject: '' > into: [ :str :each | str , each , ', ' ]) , 'and ' , gifts last ] > > and critiz says I should use a stream . > > How can I make this work ? > > Roelof > > >

May 16, 2019

can I do this with a stream or a format

by Roelof Wobben

May 16, 2019