Hi Ben， Thank you very much, your answer make me clear like water. My question aimed on where, which type errors occur when perform a message. My usecase. when perform: aMessage(with a space), get DNU error , cannot find out by eyes directly.
asMessage is better than asSymbol. Cheers Bing At 2017-02-12 00:39:55, "Ben Coman" <b...@openinworld.com> wrote: >Hi Bing Liang, > >Thanks for your comments. Fresh eyes provide interesting perspectives >on things we take for granted. > >On Sat, Feb 11, 2017 at 4:41 PM, lb <liangbin...@126.com> wrote: >> Thank you, Sven >> gradually clear. >> 1. Symbol as String subclass, only guarantees a symbol object only one in >> system, use ==; >> 2. keywords (selector name method name) are spectial symbols, without space >> or forbided characters; >> 3. perform: aSymbol, means perform: aKeyword, > >Not exactly. It means perform a "message" where there are three types >of messages... >* unary, like #printString >* binary, like #+ >* keyword, like #perform: or >#subclass:instanceVariableNames:classVariableNames:package: >having a colon appended to each keyword > >> Should we add asKeyword to String, >> let >> perform: aString asKeyword > >or alternatively per above... perform: aString asMessage > >> not >> perform: aString asSymbol ? > >In the case that aString contained a space, >presumably #asMessage would produce a runtime error in asMessage >whereas #asSymbol would produce a runtime error in #perform: >I guess there is a minor benefit of failing early but will that make >much difference in practice. >Do you have a use case where it makes a major difference? > > >> At 2017-02-11 15:51:49, "Sven Van Caekenberghe" <s...@stfx.eu> wrote: >>>Hi Bing, >>> >>>Yes, any character is allowed in a Symbol. There is even special syntax >>> that allows such Symbols to be represented literally. >>> >>>'a b' asSymbol. >>> >>> => #'a b' >>> >>>Although it might be confusing, I don't see any problem. >>> >>>The concept of 'meaning' is defined by the user, the usage, not by the >>> Symbol itself. A Symbol with a space cannot be a selector (message/method) >>> name, but that does not mean a Symbol with a space could not be useful in >>> some other context. >>> >>>> On 11 Feb 2017, at 05:56, lb <liangbin...@126.com> wrote: >>>> >>>> Hi, >>>> I know Symbol is subclass of String. >>>> Any string object can become symbol object by sending 'asSymbol' >>>> message.. >>>> I think symbol must has its meaning in common use, so the symbol should >>>> be composed of alphabet or number ‘without space“. > >Different domains have different common usage. >IIUC, Smalltalk's definition of symbol is from the 1970s. >Pharo is not overly constrained by Smalltalk traditions, but there >must be sufficient gain to balance deviations from consistency with >other Smalltalks. > >>>> >>>> BUT There are not compliant below >>>> 1. ' ' asSymbol >>>> no meaning >>>> 2. '$%%&' asSymbol >>>> no meaning >>>> 3. 'sign' asSymbol = 'sign ' asSymbol >>> false because of space. >>>> 3. ' one two three ' asSymbol >>> I think It should >>>> become three symbols = #one, #two, #three >>>> >>>> >>>> Maybe my understanding is wrong. > >no problem. Being wrong is a great way to learn ;) > >cheers -ben >
