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digitalmars.D.learn - Convert string to wchar.

reply Jacob Carlborg <doob me.com> writes:
I tried to convert a string into a wchar, but that didn't compile 
because of this template constraint:

https://github.com/D-Programming-Language/phobos/blob/master/std/conv.d#L1770

Is there a way to convert a string into a wchar?

-- 
/Jacob Carlborg
Aug 02 2011
parent reply "Jonathan M Davis" <jmdavisProg gmx.com> writes:
 I tried to convert a string into a wchar, but that didn't compile
 because of this template constraint:
 
 https://github.com/D-Programming-Language/phobos/blob/master/std/conv.d#L17
 70
 
 Is there a way to convert a string into a wchar?


Does that even make sense? What do you want it to do, convert the first code 
point to a wchar and throw if there's more than one character in the string? 
That's like asking whether you can covert between a container of ints and an 
int. I would never expect std.conv.to to support that. Not to mention, you 
shouldn't normally be using char or wchar by themselves, because they might 
not be valid code points. Normally, only dchar should be used when 
representing an individual character. If you want this, I'd suggest that you 
simply do something like

cast(wchar)str.front

What you're asking for is inherently unsafe as far as unicode goes.

- Jonathan M Davis
Aug 02 2011
parent reply Jacob Carlborg <doob me.com> writes:
On 2011-08-02 19:51, Jonathan M Davis wrote:

 I tried to convert a string into a wchar, but that didn't compile
 because of this template constraint:

 https://github.com/D-Programming-Language/phobos/blob/master/std/conv.d#L17
 70

 Is there a way to convert a string into a wchar?


 Does that even make sense? What do you want it to do, convert the first code
 point to a wchar and throw if there's more than one character in the string?
 That's like asking whether you can covert between a container of ints and an
 int. I would never expect std.conv.to to support that. Not to mention, you
 shouldn't normally be using char or wchar by themselves, because they might
 not be valid code points. Normally, only dchar should be used when
 representing an individual character. If you want this, I'd suggest that you
 simply do something like

 cast(wchar)str.front

 What you're asking for is inherently unsafe as far as unicode goes.

 - Jonathan M Davis


I'm working on a serialization library and I intend to support as many 
types as possible. So if someone serializes a single wchar I need to be 
able to deserialize it. Since the serialized data is represented by a 
string, in this case, I need to convert a string containing a single 
character to a wchar when deserializing.

Yes, convert the first code point to a wchar and then throw if there's 
more the one character in the string.

-- 
/Jacob Carlborg
Aug 02 2011
next sibling parent reply Jonathan M Davis <jmdavisProg gmx.com> writes:
On Wednesday 03 August 2011 08:29:09 Jacob Carlborg wrote:

 On 2011-08-02 19:51, Jonathan M Davis wrote:

 I tried to convert a string into a wchar, but that didn't compile
 because of this template constraint:
 
 https://github.com/D-Programming-Language/phobos/blob/master/std/conv.
 d#L17 70
 
 Is there a way to convert a string into a wchar?


 
 Does that even make sense? What do you want it to do, convert the first
 code point to a wchar and throw if there's more than one character in
 the string? That's like asking whether you can covert between a
 container of ints and an int. I would never expect std.conv.to to
 support that. Not to mention, you shouldn't normally be using char or
 wchar by themselves, because they might not be valid code points.
 Normally, only dchar should be used when representing an individual
 character. If you want this, I'd suggest that you simply do something
 like
 
 cast(wchar)str.front
 
 What you're asking for is inherently unsafe as far as unicode goes.
 
 - Jonathan M Davis


 
 I'm working on a serialization library and I intend to support as many
 types as possible. So if someone serializes a single wchar I need to be
 able to deserialize it. Since the serialized data is represented by a
 string, in this case, I need to convert a string containing a single
 character to a wchar when deserializing.
 
 Yes, convert the first code point to a wchar and then throw if there's
 more the one character in the string.


Well, while it's understandable that you have to cover pretty every possible 
case of converting to and from a string with what you're doing, I don't think 
that it's at all reasonable to have std.conv.to convert a string to any 
character type, let alone one other than dchar. It's almost always a horrible 
idea and should _not_ be encouraged. So, I'd advise you to just find a way to 
deal with it appropriately in your own code. I think that it would be a very 
bad idea for std.conv.to or anything else in Phobos to support such a 
conversion.

- Jonathan M Davis
Aug 02 2011
parent Jacob Carlborg <doob me.com> writes:
On 2011-08-03 08:38, Jonathan M Davis wrote:

 On Wednesday 03 August 2011 08:29:09 Jacob Carlborg wrote:

 On 2011-08-02 19:51, Jonathan M Davis wrote:

 I tried to convert a string into a wchar, but that didn't compile
 because of this template constraint:

 https://github.com/D-Programming-Language/phobos/blob/master/std/conv.
 d#L17 70

 Is there a way to convert a string into a wchar?


 Does that even make sense? What do you want it to do, convert the first
 code point to a wchar and throw if there's more than one character in
 the string? That's like asking whether you can covert between a
 container of ints and an int. I would never expect std.conv.to to
 support that. Not to mention, you shouldn't normally be using char or
 wchar by themselves, because they might not be valid code points.
 Normally, only dchar should be used when representing an individual
 character. If you want this, I'd suggest that you simply do something
 like

 cast(wchar)str.front

 What you're asking for is inherently unsafe as far as unicode goes.

 - Jonathan M Davis


 I'm working on a serialization library and I intend to support as many
 types as possible. So if someone serializes a single wchar I need to be
 able to deserialize it. Since the serialized data is represented by a
 string, in this case, I need to convert a string containing a single
 character to a wchar when deserializing.

 Yes, convert the first code point to a wchar and then throw if there's
 more the one character in the string.


 Well, while it's understandable that you have to cover pretty every possible
 case of converting to and from a string with what you're doing, I don't think
 that it's at all reasonable to have std.conv.to convert a string to any
 character type, let alone one other than dchar. It's almost always a horrible
 idea and should _not_ be encouraged. So, I'd advise you to just find a way to
 deal with it appropriately in your own code. I think that it would be a very
 bad idea for std.conv.to or anything else in Phobos to support such a
 conversion.

 - Jonathan M Davis


Ok, fair enough.

-- 
/Jacob Carlborg
Aug 03 2011
prev sibling parent reply Pelle <pelle.mansson gmail.com> writes:
On Wed, 03 Aug 2011 08:29:09 +0200, Jacob Carlborg <doob me.com> wrote:

 Yes, convert the first code point to a wchar and then throw if there's  
 more the one character in the string.


Not tested, and I might be wrong, but 'to!' should work between dchar and  
wchar, no?

wchar to_wchar(string s) {
     auto c = s.front;
     s.popFront();
     assert (s.empty);
     return to!wchar(c);
}
Aug 03 2011
next sibling parent Jonathan M Davis <jmdavisProg gmx.com> writes:
On Wednesday 03 August 2011 09:34:53 Pelle wrote:

 On Wed, 03 Aug 2011 08:29:09 +0200, Jacob Carlborg <doob me.com> wrote:

 Yes, convert the first code point to a wchar and then throw if there's
 more the one character in the string.


 
 Not tested, and I might be wrong, but 'to!' should work between dchar and
 wchar, no?
 
 wchar to_wchar(string s) {
      auto c = s.front;
      s.popFront();
      assert (s.empty);
      return to!wchar(c);
 }


It's debatable as to whether std.conv.to should be able to convert between 
code units like that (you _really_ shouldn't ever be using char or wchar 
outside of arrays or other ranges), but it does appear to compile, for better 
or worse.

- Jonathan M Davis
Aug 03 2011
prev sibling next sibling parent Jonathan M Davis <jmdavisProg gmx.com> writes:
On Wednesday 03 August 2011 01:02:02 Jonathan M Davis wrote:

 On Wednesday 03 August 2011 09:34:53 Pelle wrote:

 On Wed, 03 Aug 2011 08:29:09 +0200, Jacob Carlborg <doob me.com> wrote:

 Yes, convert the first code point to a wchar and then throw if
 there's
 more the one character in the string.


 
 Not tested, and I might be wrong, but 'to!' should work between dchar
 and
 wchar, no?
 
 wchar to_wchar(string s) {
 
      auto c = s.front;
      s.popFront();
      assert (s.empty);
      return to!wchar(c);
 
 }


 
 It's debatable as to whether std.conv.to should be able to convert between
 code units like that (you _really_ shouldn't ever be using char or wchar
 outside of arrays or other ranges), but it does appear to compile, for
 better or worse.


It looks like the conversion works as long as the character in question will 
fit in the character type that you're converting to. If it doesn't fit, then it 
throws. So, it's as safe as such a conversion can be (though it still isn't 
generally a good idea to use individual chars or wchars in code).

- Jonathan M Davis
Aug 03 2011
prev sibling parent Jacob Carlborg <doob me.com> writes:
On 2011-08-03 09:34, Pelle wrote:

 On Wed, 03 Aug 2011 08:29:09 +0200, Jacob Carlborg <doob me.com> wrote:

 Yes, convert the first code point to a wchar and then throw if there's
 more the one character in the string.


 Not tested, and I might be wrong, but 'to!' should work between dchar
 and wchar, no?

 wchar to_wchar(string s) {
 auto c = s.front;
 s.popFront();
 assert (s.empty);
 return to!wchar(c);
 }


Ok, thanks.

-- 
/Jacob Carlborg
Aug 03 2011