www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - Tagged enums why reserved words are not permitted ?

reply "Domingo" <mingodad gmail.com> writes:
Hello !

I'm not sure if I'm missing something here but for a tagged enum 
it doesn't seem to make sense to forbid reserved keywords like:

enum CrudOps {read, write, delete}

The dmd compiler are complaining:
------
cte.d(4): Error: basic type expected, not delete
cte.d(4): Error: no identifier for declarator int
cte.d(4): Error: type only allowed if anonymous enum and no enum 
type
cte.d(4): Error: if type, there must be an initializer
cte.d(4): Error: found 'delete' when expecting ','
------

It doesn't make sense to me because this kind of enum will not 
polute the global space and always need to beused with the tag: 
CrudOps.delete

I'm missing something here ?

Cheers !
Oct 27 2014
next sibling parent reply Jonathan M Davis via Digitalmars-d-learn writes:
On Tuesday, October 28, 2014 00:31:43 Domingo via Digitalmars-d-learn wrote:

 Hello !

 I'm not sure if I'm missing something here but for a tagged enum
 it doesn't seem to make sense to forbid reserved keywords like:

 enum CrudOps {read, write, delete}

 The dmd compiler are complaining:
 ------
 cte.d(4): Error: basic type expected, not delete
 cte.d(4): Error: no identifier for declarator int
 cte.d(4): Error: type only allowed if anonymous enum and no enum
 type
 cte.d(4): Error: if type, there must be an initializer
 cte.d(4): Error: found 'delete' when expecting ','
 ------

 It doesn't make sense to me because this kind of enum will not
 polute the global space and always need to beused with the tag:
 CrudOps.delete

 I'm missing something here ?


keywords are always keywords wherever they are in the code and are only legal
where those keywords are legal. I can see how you could come to the conclusion
that the compiler shouldn't think that you're trying to use a keyword as an
enum member, but the compiler does not take that into account. And I've never
seen a language where it did (though one may exist out there somewhere). The
thing that's been done in Phobos in this type of situation is to put an
underscore on the end of the keyword, so you'd get

enum CrudOps { read, write, delete_ }

and while that may not be what you want, it's pretty much the best that you
can do.

- Jonathan M Davis
Oct 27 2014
next sibling parent Jacob Carlborg <doob me.com> writes:
On 2014-10-28 01:51, Jonathan M Davis via Digitalmars-d-learn wrote:


 And I've never seen a language where it did (though one may exist out there
somewhere)


Ruby:

class Foo
end



You always need to have a receiver when calling the "class" method. This 
is not uncommon at all, it's needed (or one way to do it) when accessing 
class methods (static methods) from inside of a method

class Bar

   end

   def baz
   end

   def bar
     baz

   end
end

In fact, in Ruby you can use any name for a method, but you might not be 
able to declare it, or call it :). Instead one can use metaprogramming 
and reflection:

class Bar

     puts "calling foo bar"
   end
end



CoffeeScript:

class Foo
   bar: ->
     console.log "bar"

a = { class: "foo" }


-- 
/Jacob Carlborg
Oct 28 2014
prev sibling parent reply "Gary Willoughby" <dev nomad.so> writes:
On Tuesday, 28 October 2014 at 00:51:17 UTC, Jonathan M Davis via 
Digitalmars-d-learn

 The
 thing that's been done in Phobos in this type of situation is 
 to put an
 underscore on the end of the keyword, so you'd get

 enum CrudOps { read, write, delete_ }

 and while that may not be what you want, it's pretty much the 
 best that you
 can do.

 - Jonathan M Davis


This is also mentioned in the style guide too.

http://dlang.org/dstyle.html
Oct 28 2014
parent Jonathan M Davis via Digitalmars-d-learn writes:
On Tuesday, October 28, 2014 16:58:50 Gary Willoughby via Digitalmars-d-learn 
wrote:

 On Tuesday, 28 October 2014 at 00:51:17 UTC, Jonathan M Davis via
 Digitalmars-d-learn


 The
 thing that's been done in Phobos in this type of situation is
 to put an
 underscore on the end of the keyword, so you'd get

 enum CrudOps { read, write, delete_ }

 and while that may not be what you want, it's pretty much the
 best that you
 can do.

 - Jonathan M Davis


 This is also mentioned in the style guide too.

 http://dlang.org/dstyle.html


So, it is. I'd forgotten about that (even though I'm almost certainly the
one who put it there). But that's what we decided on when it came up in
std.traits a while back. It seemed like the only good way to use a keyword
as an identifier without breaking the naming conventions by doing something
like capitalizing it differently.

- Jonathan M Davis
Oct 28 2014
prev sibling next sibling parent ketmar via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:
On Tue, 28 Oct 2014 00:31:43 +0000
Domingo via Digitalmars-d-learn <digitalmars-d-learn puremagic.com>
wrote:


 Hello !
=20
 I'm not sure if I'm missing something here but for a tagged enum=20
 it doesn't seem to make sense to forbid reserved keywords like:
=20
 enum CrudOps {read, write, delete}
=20
 The dmd compiler are complaining:
 ------
 cte.d(4): Error: basic type expected, not delete
 cte.d(4): Error: no identifier for declarator int
 cte.d(4): Error: type only allowed if anonymous enum and no enum=20
 type
 cte.d(4): Error: if type, there must be an initializer
 cte.d(4): Error: found 'delete' when expecting ','
 ------
=20
 It doesn't make sense to me because this kind of enum will not=20
 polute the global space and always need to beused with the tag:=20
 CrudOps.delete
=20
 I'm missing something here ?
=20
 Cheers !


D has no "context keywords". i.e. no keyword can be used as identifier,
even if it's possible to distinguish between use cases. you can't, for
example, use "body" identifier for variable/field name (and this annoys
me alot).

i believe that this was done so source code analyzing tools can stop
tracking context while parsing D source. i.e. tool is not required to
do semantic analysis to determine if "body" is identifier or function
body start.

i don't think that this will change. and this is the reason, for
example, for adding " property", " safe", " trusted" and so on instead
of "property", "safe", "trusted": D taken some valuable keywords
already and nobody wants to lose even more names. ;-)
Oct 27 2014
prev sibling next sibling parent "H. S. Teoh via Digitalmars-d-learn" <digitalmars-d-learn puremagic.com> writes:
On Tue, Oct 28, 2014 at 12:31:43AM +0000, Domingo via Digitalmars-d-learn wrote:

 Hello !
 
 I'm not sure if I'm missing something here but for a tagged enum it
 doesn't seem to make sense to forbid reserved keywords like:
 
 enum CrudOps {read, write, delete}
 
 The dmd compiler are complaining:
 ------
 cte.d(4): Error: basic type expected, not delete
 cte.d(4): Error: no identifier for declarator int
 cte.d(4): Error: type only allowed if anonymous enum and no enum type
 cte.d(4): Error: if type, there must be an initializer
 cte.d(4): Error: found 'delete' when expecting ','
 ------
 
 It doesn't make sense to me because this kind of enum will not polute
 the global space and always need to beused with the tag:
 CrudOps.delete


[...]

Not true:

	CrudOps x;
	with (CrudOps) {
		x = read;
		... // etc.
	}


T

-- 
In a world without fences, who needs Windows and Gates? -- Christian Surchi
Oct 27 2014
prev sibling parent Steven Schveighoffer <schveiguy yahoo.com> writes:
On 10/27/14 8:31 PM, Domingo wrote:

 Hello !

 I'm not sure if I'm missing something here but for a tagged enum it
 doesn't seem to make sense to forbid reserved keywords like:

 enum CrudOps {read, write, delete}

 The dmd compiler are complaining:
 ------
 cte.d(4): Error: basic type expected, not delete
 cte.d(4): Error: no identifier for declarator int
 cte.d(4): Error: type only allowed if anonymous enum and no enum type
 cte.d(4): Error: if type, there must be an initializer
 cte.d(4): Error: found 'delete' when expecting ','
 ------

 It doesn't make sense to me because this kind of enum will not polute
 the global space and always need to beused with the tag: CrudOps.delete

 I'm missing something here ?

 Cheers !


http://en.wikipedia.org/wiki/Reserved_word

"Making keywords be reserved words makes lexing easier, as a string of 
characters will unambiguously be either a keyword or an identifier, 
without depending on context"

-Steve
Oct 28 2014