Re: [C++-11] User defined literals

[Ed Smith-Rowland <3dw4rd@verizon.net>]

On 10/21/2011 05:20 PM, Jason Merrill wrote:
> I think we're down to minor cosmetic issues:
>
> On 10/21/2011 03:55 PM, Tom Tromey wrote:
>> There are a few spots like this that are missing a space before an open
>> paren.
>
>> +      if (DECL_LANGUAGE(decl) == lang_c)
>
> Another one.
>
>> -          if (warn_cxx0x_compat
>> - && C_RID_CODE (token->u.value) >= RID_FIRST_CXX0X
>> - && C_RID_CODE (token->u.value) <= RID_LAST_CXX0X)
> ....
>
> This code doesn't seem to have actually changed, so let's not adjust 
> its whitespace.
>
>> +  /* Fill in PARMVEC with all of the parameters.  */
>> +  parmvec = make_tree_vec (len);
>
> Let's call it 'charvec'; the characters are template arguments, not 
> parameters.
>
>> +/* Parse a user-defined numeric constant.  returns a call to a 
>> user-defined
>> +   literal operator.  */
>> +static tree
>> +cp_parser_userdef_numeric_literal (cp_parser *parser)
>
> Add a blank line between comment and function.
>
>> While looking at the embedded string issue I found that if you apply 
>> the suffix of a raw literal to a string it errors as it should but 
>> the error complained that there were too many arguments for the 
>> function.  This was not helpful so I made a nicer error message.
>
>> +  if (result == error_mark_node)
>> +    error ("invalid string literal prefix %<\"%s\"%> for user-defined"
>> +          " raw literal operator %qD", TREE_STRING_POINTER (value), 
>> name);
>
> I think that we want a combination of the two errors; the new error 
> doesn't help the user to fix their code as much.  It should remind 
> them that for a string literal the function is called with a length 
> argument as well.
>
Concerning this error, the only way to get here is to mis-use a raw 
literal operator by giving it a quoted string.  The prefix must be 
interpretable as a number of some kind.  I think I'll tell the user to 
drop the quotes.
The length of a string literal is supplied implicitly by the compiler to 
a string literal operator when a string user defined literal is 
encountered.  The user doesn't explicitly call the operator (not here 
anyway).

>> +       error ("literal operator template %qD has invalid parameter 
>> list",
>> +              decl);
>
> Similarly, this message should say that the parameter list needs to be 
> <char...>
>
>>
>> +
>> +/* Return true if a user-defined literal operator is a raw 
>> operator.  */
>> +
>
> We don't need the extra newline before the comment.
>
> Should be ready to go with these tweaks.
>
> Jason
>
I've made these corrections.  They'll be in the next patch.

Unfortunately, as I was testing raw operators on very long strings I 
observed two things:
1. A bad error - the argument to a raw literal operator must be a 
null-terminated string.
2. If a very long number is given as the prefix to a numeric literal, a 
warning is issued ("integer constant is too large for its type")
If the receiving operator is either the raw operator or the operator 
template then this should not be given.  I anticipate people might like 
to have multi-precision numbers someday, for example.

Before I release another patch I have to fix 1.  The warning might be 
fixed in-tree if that's OK.

Ed