Newsgroups: comp.lang.c
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Union initialization
Message-ID: <1989Feb27.165348.16099@utzoo.uucp>
Organization: U of Toronto Zoology
References: <816@atanasoff.cs.iastate.edu> <16019@mimsy.UUCP> <51116@yale-celray.yale.UUCP> <609@maths.tcd.ie>
Date: Mon, 27 Feb 89 16:53:48 GMT

In article <609@maths.tcd.ie> ch@maths.tcd.ie (Charles Bryant) writes:
>[proposal in which compiler guesses which member based on type of initializer
>expression]
>
>Perhaps this would be too much of a special case for the compiler...

It's too much of a special case for the language designer, too, I'm afraid.
This particular suggestion always seems to come up.  It doesn't work very
well.  How do you initialize a struct inside a union?  (Cast to the struct
type?  Now we have a unique situation in which such casts are legal.)  What
about a union inside the union?  Is a string an initializer for a "char *"
or a "char []"?  Do implicit conversions get done?  (If so, chaos.  If not,
we now have a unique situation in which they aren't.)  If there are both
int and long members, which one gets initialized if the initializer is,
say, 75000 (the type of which is implementation-dependent)?  Is the cast
mandatory?  (If so, we now have a unique etc. etc.)

There are just too many problems with guessing member based on type.  It
really has to be done by name or position.
-- 
The Earth is our mother;       |     Henry Spencer at U of Toronto Zoology
our nine months are up.        | uunet!attcan!utzoo!henry henry@zoo.toronto.edu