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From: prophet36NOSPM@hotmail.com (Chris McClelland)
Newsgroups: comp.std.c++
Subject: Re: new meaning of explicit keyword
Date: Thu, 10 Jan 2002 18:40:58 GMT
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Interesting.

I'd like to be able to use explicit on cast operators, to force an
explicit cast. Like this:

class X {
public:
  X(float val) {...}
  explicit operator float() {...}
};

int main() {
    float a = 10.3f;
    X b = a;  // Fine. Use X(float)
    float c = b;  // Error!!
    float d = static_cast<float>(b);  // Fine...
    float e = (float)b;  // Also fine...
}

Sean Parent has provided a nice workaround for those of us who have
the luxury of standard-compliant compilers:
http://groups.google.com/groups?q=explicit+cast&hl=en&selm=B718ED17.1502D%25sparent%40adobe.com&rnum=3

- Chris


"Sektor van Skijlen" <sektor@spam-buffer.aldec.com> wrote in message news:<a1hsph$p4k$1@news.tpi.pl>...
> For now, the "explicit" keyword allows a type CONSTRUCTOR to
> disallow implicit conversions into this type. This keyword could be
> also used to signify, that this implicit conversion is not allowed for
> the object initialization. For example:
> 
> int x = 'c'; // allowed
> explicit int x = 'c'; // not allowed!
> explicit int x = int( 'c' ); // allowed
> 
> This feature could be mostly used in a situation, where the implicit
> conversion, granted by standard, is a disadvantage in some cases.
> For example, one of std::string's constructors take two arguments,
> which mean an amount of characters and a character. The
> disadvantage is that the compiler won't see any error if you pass
> arguments in wrong order. This will be passed, because there
> will be ALLOWED conversion from char to size_t and in reverse.
> This bug is always hard to detect.
> 
> Using this feature you can state:
> 
> string( size_t size, explicit char ch );
> 
> And then this:
> 
> string s( 'c', 12 );
> 
> won't compile, because "12" can't be implicitly converted to char.
> However it can be worked around:
> 
> string s( 'c', char( 12 ) );
> 
> 
> Regards,
> --
> ((
>  )) ektor
> 
> 
> ---
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