Semantics of toString

[Yigal Chripun]

On 06/11/2009 12:34, Pelle Månsson wrote:
> Yigal Chripun wrote:
>> On 06/11/2009 07:34, Don wrote:
>>> Nick Sabalausky wrote:
>>>> "Don" <nospam at nospam.com> wrote in message
>>>> news:hcvf9l$91i$1 at digitalmars.com...
>>>>> Justin Johansson wrote:
>>>>>> So what does "toString" mean to you?
>>>>> It's a hack from the early days of D. Should be unavailable unless
>>>>> the -debug flag is set, to discourage people from using it. I hate it.
>>>>>
>>>>
>>>> What don't you like about it?
>>>>
>>>
>>> It cannot even do the most basic stuff.
>>> (1) You can't even make a struct that behaves like an int.
>>>
>>> struct MyInt
>>> {
>>> int z;
>>> string toString() { .... }
>>> }
>>>
>>> void main()
>>> {
>>> int a = 400;
>>> MyInt b = 400;
>>> writefln("%05d %05d", a, b);
>>> writefln("%x %x", a, b);
>>> }
>>>
>>> (2) It doesn't behave like a stream. Suppose you have XmlDoc.toString()
>>> You can't emit the doc, piece by piece. You have to create the ENTIRE
>>> string in one go!
>>>
>>>
>>
>> The first issue you raise is IMO a problem with writefln and not with
>> toString since writefln doesn't handle user-defined types properly.
>>
>> I think that writefln (btw, horrible name) should only deal with
>> strings and their formatting and all other types need to provide an
>> (optionally formatted) string.
>> a numeric type would provide formatting of properties like number of
>> decimal places, thousands separator, etc while user defined
>> specification type could provide a type of standard format.
>>
>> auto spec = new Specification(HTML);
>> string ansi = spec.toString(Specification.ANSI);
>> string iso = spec.toString(Specification.ISO);
>> writefln ("{1} {0}", ansi, iso); // i'm using the tango/C# formatting
>>
>> the c style format string that specifies types is a horrible horrible
>> thing and should be removed.

> How do you do %.3f in {}-notation?

writefln("{0:F3}", value);

> Your formatting string should be written as writeln(ansi, " ", iso);

That is incorrect since in my example I use the format string to switch 
the order of the strings. ( hence the numbers inside the {} )

Please go and read the tango documentation starting with 
http://www.dsource.org/projects/tango/wiki/TutCSharpFormatter
it has also links to the MSDN docs which describe the modifiers:
for instance:
http://msdn.microsoft.com/en-us/library/dwhawy9k%28VS.100%29.aspx

This is one area in phobos that needs to be rewritten from scratch or 
better yet, use tango. I'm still waiting for when hell will freeze over 
and tango and phobos will be merged together in one consistent API.